eMedicine - The Role of Sentinel Node Biopsy in Skin Cancer : Article by Tina J Hieken

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The Role of Sentinel Node Biopsy in Skin Cancer

Article Last Updated: Sep 15, 2006

The incidence of malignant melanoma is increasing rapidly, at a rate of 4-8% per year. Malignant melanoma typically affects young patients (median age 45 y). The lifetime risk of developing melanoma for a person born in the United States is now estimated to be 1 in 64. Historically, the treatment of malignant melanoma has been primarily surgical, and it remains largely so despite recent advances in adjuvant therapy.

The natural history of cutaneous melanoma is most often an orderly progression from invasion at the primary site, to regional lymph nodes via dermal lymphatics, and then to distant sites. If a melanoma is identified and treated at an early stage, the likelihood of synchronous lymph node metastases is quite low, and patients are usually treated with wide local excision alone. While much effort has been directed toward using molecular, cellular, and biochemical markers to determine the prognosis and appropriate treatment of melanoma, the presence or absence of lymph node metastases remains the most powerful predictor of outcome. Numerous studies support that sentinel lymph node status is the most important independent prognostic factor with respect to disease progression and melanoma-specific survival.

One indicator of the degree to which sentinel lymph node biopsy with selective lymph node dissection has been accepted in the staging and treatment of melanoma is the latest American Joint Commission on Cancer (AJCC) staging guidelines for melanoma, which, for the first time, incorporate nodal microstaging and discriminate between microscopic and macroscopic nodal disease. Additionally, the National Comprehensive Cancer Network (NCCN) guidelines for the treatment of melanoma include sentinel lymph node biopsy with selective lymph node dissection in their treatment algorithms. Over the past 15 years as this technique has gained acceptance, it has been refined.

The sentinel lymph node concept is that a primary or sentinel lymph node (or nodes) exists through which tumor cells from a primary tumor in a particular location first must travel to spread to a particular regional lymph node basin. A tracer substance injected into the dermis at the primary tumor site provides a roadmap leading to the sentinel lymph node(s). In addition, the hypothesis that careful examination of the sentinel lymph node(s) indicates the status of the entire lymph node basin has been validated in several studies. Thus, sentinel lymph node biopsy with selective lymph node dissection has been embraced as an alternative to elective lymphadenectomy or observation for patients with clinically negative regional lymph nodes who are at high risk for nodal metastases.

The objectives of combining sentinel lymph node biopsy with selective lymphadenectomy in clinical practice include both decreasing the extent of the operation for selected patients (decreasing the number of nontherapeutic lymphadenectomies) and increasing the identification rate of occult lymph node metastases (increasing the accuracy of staging) by providing the pathologist with the lymph node (or nodes) most likely to contain metastatic disease. Evidence of a survival benefit for elective lymph node dissection in selected melanoma patients, as well as immunohistochemical- and molecular-based detection of metastatic melanoma in lymph nodes deemed negative by standard histopathology, implies that some patients are understaged by conventional techniques.

The World Health Organization truncal melanoma trial (#14) found a significant improvement in 5-year survival rates (48% vs 26%, P = .04) for patients with clinically occult metastatic lymph nodes who underwent elective lymph node dissection at the time of wide local excision versus patients who underwent therapeutic lymph node dissection after developing clinically detectable lymphadenopathy.

In addition, a second randomized, prospective, multi-institutional study, the Intergroup Melanoma Trial, revealed a significant improvement in 10-year overall survival for patients who underwent elective lymph node dissection versus wide excision in several prospectively stratified subgroups. Results indicated a 30% reduction in 10-year mortality rates for patients with nonulcerated melanomas (overall survival 84% vs 77%, P =.03), a 27% reduction in 10-year mortality rates for patients with melanomas from 1-2 mm thick (overall survival 86% vs 80%, P = .3), and a 27% reduction in 10-year mortality rates for patients with extremity melanomas (overall survival 84% vs 78%).

The objective of sentinel lymph node biopsy is to identify the 20-25% of patients who present with clinically occult regional disease (AJCC stage IIIA and some IIIB). Sentinel lymph node biopsy also (1) minimizes the morbidity associated with elective lymphadenectomy for melanoma patients by identifying those most likely to benefit from lymphadenectomy after a minor outpatient procedure with a much diminished risk of lymphedema and other complications, (2) identifies patients who may benefit from postoperative adjuvant therapy and those who may avoid adjuvant therapy, and (3) provides a means for homogeneous stratification of patients for and within randomized clinical trials.

The technique of sentinel lymph node biopsy with selective lymph node dissection has been widely adopted by surgical oncologists, which has resulted in its use in the treatment of other cutaneous and noncutaneous malignancies with regional lymphatic metastatic potential.

History of the Procedure

Sentinel lymph node biopsy first was described more than 50 years ago and was used to stage carcinoma of the penis. As an alternative to elective node dissection in melanoma, sentinel lymph node biopsy was first proposed by Morton, who used blue dye injected around the primary melanoma to identify the sentinel node. In 1992, in his initial report of 223 patients using vital blue dye alone, the sentinel lymph node was identified in 194 (82%) of 237 lymph node basins, 40 (21%) patients had metastatic disease in the sentinel lymph node, and 2 patients had falsely negative sentinel nodes (accuracy 99%, false-negative rate 4.8%).

Lymphoscintigraphy has been used since the 1950s to delineate lymphatic drainage pathways, first with radioactive colloid gold and, currently, with technetium Tc 99m sulfur colloid, albumin colloid, or human serum albumin. Antimony sulfide colloid, not available in the United States, is commonly used in Australia. In 1993, both Morton et al and Alex and Krag described radioguided sentinel lymph node biopsy with gamma-probe localization of sentinel lymph nodes. This method permits transcutaneous identification of the hot sentinel lymph node and performance of biopsy through a small incision; it also helps limit the extent of the dissection needed to identify the sentinel lymph node.

Proper selection of patients for sentinel lymph node biopsy with selective lymphadenectomy is an important aspect of the procedure. Typically, the procedure is recommended for patients in whom the estimated risk of lymph node metastases is at least 10%. Appropriate candidates include patients with clinically node-negative melanomas thicker than or equal to 1 mm. While general agreement exists that sentinel lymph node biopsy is indicated for patients with intermediate-thickness melanomas (1-4 mm thick), debate continues among surgical oncologists regarding the expansion of these indications to patients with thinner or thicker tumors.

Most clinicians agree that sentinel lymph node biopsy is not indicated for patients with tumors thinner than 0.75 mm because the yield is 0% in most large series and less than 2% in a few others. Patients with high-risk lesions of 0.75-0.99 mm should be considered for sentinel lymph node biopsy if their melanoma is Clark level IV or V or is ulcerated. The likelihood of identifying a sentinel lymph node containing metastatic disease in these patients remains quite low (approximately 5%), while the disease relapse rate may be as high as 20% at 5 years in high-risk subgroups.

Some investigators also consider melanoma patients with tumors thinner than 1 mm as candidates for sentinel lymph node biopsy if the tumors exhibit a high mitotic rate, angiolymphatic invasion, significant histologic regression, a vertical growth phase component, or an axial location. Younger patient age and male sex also are associated with an increased incidence of sentinel lymph node metastases. One series of 409 patients with melanomas 0.75-1 mm found a 5% rate of positive sentinel nodes of which half occurred in association with level II or III tumors without ulceration. They concluded that all patients with melanomas 0.75-1 mm should be offered the procedure.

Importantly, note that a preoperative determination of exact tumor thickness may not be possible in patients diagnosed based on shave biopsy results (or when the melanoma extends to the deep margin of the biopsy) or in those whose tumors are not reviewed by an experienced and meticulous dermatopathologist. Up-staging of tumor thickness has been reported to occur in up to 50% of melanoma biopsy specimens reviewed by interested dermatopathologists. Nonetheless, sentinel lymph node biopsy remains controversial for patients with thin melanomas who, overall, have an excellent long-term prognosis.

Other patients who may benefit from sentinel lymph node biopsy include patients with tumors thicker than 4 mm. In the past, a regional operation (elective lymph node dissection) was discouraged because of the high rate of concomitant occult or apparent systemic disease via hematogenous spread. After careful exclusion of patients with unresectable metastatic disease, sentinel lymph node biopsy may be considered in these patients to identify individuals with a better prognosis (negative sentinel lymph node biopsy results), to achieve long-term locoregional control of disease (selective lymphadenectomy), and to stratify patients for participation in clinical trials. Sentinel lymph node biopsy also may be considered for patients with isolated local cutaneous recurrence in the absence of clinically evident regional nodal disease.

The rationale for sentinel lymph node biopsy with selective lymphadenectomy in patients with intermediate-thickness melanoma is that the incidence of occult regional disease is significant in these patients, while the likelihood of distant metastatic disease remains quite low. Several studies suggest a survival benefit for patients treated with regional lymphadenectomy for clinically occult disease rather than delayed therapeutic lymph node dissection when nodal metastases become clinically obvious as outlined above.

No survival benefit has yet been proven for sentinel lymph node biopsy with selective lymphadenectomy for patients with clinically node-negative melanoma. Three ongoing prospective randomized clinical trials are being conducted to address this and related issues.

One subset of Spitzoid lesions is difficult to classify as clearly benign or malignant and may represent undiagnosed malignant melanoma. Sentinel lymph node biopsy may be offered to patients with atypical or borderline lesions (whose features may include size > 1 cm, ulceration, deep dermal mitoses, extension into subcutaneous fat, and cytologic atypia). In one series of such patients, 8 (44%) of 18 patients had sentinel lymph node metastases.

Recently, application of the principles of sentinel lymph node biopsy to other cutaneous malignancies with a propensity for regional lymphatic spread has garnered tremendous interest. The technique has been reported most frequently for neuroendocrine carcinoma of the skin (Merkel cell carcinoma or trabecular carcinoma), which frequently is a rapidly progressive and often fatal cutaneous cancer.

While only approximately 30% of patients with neuroendocrine carcinoma of the skin present with clinically apparent regional lymph node metastases, as many as 70% of the remainder of patients experience relapse in the regional lymph nodes within 2 years of diagnosis if the regional lymph nodes are not treated. Half the patients with regional failure develop systemic disease. The current NCCN guidelines now recommend sentinel lymph node biopsy with selective lymph node dissection for clinical stage I Merkel cell carcinoma patients.

Immunohistochemistry (with pancytokeratin AE1/AE3, cytokeratin 20, and chromogranin A antibodies) helps detect micrometastatic disease in these patients. Unlike patients with malignant melanoma, most patients with neuroendocrine carcinoma of the skin are offered adjuvant radiation therapy at the primary site. If lymph node metastases are found, the radiation field also may encompass the draining lymphatics and affected regional nodal basin(s). The combination of radiotherapy and selective lymphadenectomy improves survival compared with surgery or radiation alone. The technique of lymphatic mapping also helps identify the draining lymph node basin(s) more accurately, thereby helping avoid inadvertent treatment of the wrong nodal group. Chemotherapy may be used as an adjunct to locoregional therapy.

Sentinel lymph node biopsy has also been used to treat high-risk squamous cell carcinomas of the skin. It may be considered for patients with tumors extending into subcutaneous fat or invading deeper structures, for patients with tumors greater than 4-6 mm in depth, for patients with extensive peritumoral lymphatic invasion, for patients with Marjolin ulcer, and for some patients with locally recurrent carcinomas.

The authors, and others, have also applied this technique to the staging and treatment of eccrine and apocrine skin carcinomas, porocarcinoma, hidradenocarcinoma, and invasive extramammary Paget disease, which have a significant risk of lymphatic metastasis. Sentinel lymph node biopsy is also used to treat selected patients with cutaneous lymphomas and sarcomas. A report has been published that described sentinel lymph node biopsy for staging a patient with metastatic basal cell carcinoma (a rare phenomena) whose primary had evidence of malignant cells in a peritumoral dermal lymphatic vessel.

Since its initial description for melanoma patients, the concept and technique of sentinel lymph node biopsy with or without selective lymph node dissection has been applied to a number of noncutaneous malignancies with varying degrees of efficacy. Most widely accepted is sentinel lymph node biopsy for early-stage breast cancer as an alternative to routine level I and II axillary lymph node dissection.

Sentinel lymph node biopsy with selective lymphadenectomy has been used with varying degrees of success to stage noncutaneous squamous cell carcinomas of the head and neck. The importance of preoperative lymphoscintigraphy is generally acknowledged for the correct identification of the nodal basins at risk. As with melanoma of the head and neck, this alters the planned intervention in a significant number of patients. Preliminary results of a European multicenter trial suggest that this technique is valuable as the sole staging tool for early T1 and T2 oral cavity and oropharyngeal squamous cell carcinomas. This technique is now being investigated in an American College of Surgeons Oncology Group (ACOSOG) trial.

Sentinel lymph node biopsy has also been applied to the treatment of colon cancer, small bowel tumors (eg, carcinoid tumor), gastric cancer, pancreatic cancer, thyroid cancer, prostate cancer, vulvar carcinoma, penile cancer, pediatric soft tissue sarcoma, and clear cell sarcoma (melanoma of the soft parts).

The concept of sentinel lymph node biopsy is that a primary or sentinel lymph node (or nodes) exists through which tumor cells from a primary tumor in a particular location first must travel, via afferent lymphatics, to spread to a particular regional lymph node basin. The technique is well suited for application to cutaneous malignancies because of the well-developed dermal lymphatic plexus of the skin. In-transit lymph nodes also may be identified by this technique in conjunction with preoperative lymphoscintigraphy.

Several studies have demonstrated that the lymphatic drainage of melanomas of the head, neck, and trunk cannot be predicted reliably by the classic anatomic guidelines of Sappey. Lymphoscintigraphy documents direct drainage from these sites to sentinel nodes in aberrant locations, such as the triangular intermuscular space. Dual-basin drainage or interval nodes also may be identified. This finding underscores the importance of preoperative lymphoscintigraphy for these patients.

In certain clinical situations, sentinel lymph node biopsy with selective lymphadenectomy has no role. The presence of satellitosis or in-transit metastasis at the time of initial presentation is a relative contraindication to sentinel lymph node biopsy because the validity of the procedure in this setting is unknown. Patients with clinically palpable lymphadenopathy or suspected lymphadenopathy demonstrated on imaging studies (which may be confirmed by preoperative fine-needle aspiration [FNA]) should undergo a therapeutic lymph node dissection. However, in such patients with primary melanomas of the trunk or head and neck, lymphoscintigraphy should be considered to identify other nodal basins at risk, and sentinel lymph node biopsy in these areas may be performed in conjunction with therapeutic lymphadenectomy of the clinically involved nodal basin.

Lymph node biopsy with selective lymphadenectomy should not be performed if the patient has undergone a prior wide local excision with a large rotation flap closure or a very wide excision with skin graft coverage. In these patients, the pattern of lymphatic drainage is altered and lymphatic mapping and sentinel lymph node biopsy may be unreliable and inaccurate. The situation is similar in patients who have undergone prior surgery involving the regional nodal basin, such as open lymph node biopsy or skin grafting, or prior surgery that disrupts the native lymphatic drainage patterns between the primary site and the at-risk nodal basin. Elective lymph node dissection may be discussed with these patients; however, sentinel lymph node biopsy has been reported to be successful in a small series of patients with recurrent disease who had undergone previous lymph node surgery, suggesting that this area of research merits further investigation.

For patients who have undergone prior wide local excision with margins of 1-2 cm with simple advancement closure, sentinel lymph node biopsy with selective lymphadenectomy is performed, but the accuracy is slightly decreased and the number of sentinel nodes harvested per basin from these patients is higher (average 3.5 lymph nodes) than from patients who have undergone only a diagnostic biopsy of the primary melanoma. In addition, misidentification of the at-risk nodal basin by preoperative lymphoscintigraphy performed after wide local excision has been reported, especially in areas of ambiguous lymphatic drainage. This emphasizes the importance of referring patients for sentinel node biopsy prior to definitive treatment of their primary melanoma.

Other situations merit special consideration. Pregnant women should not undergo sentinel lymph node biopsy with a radioactive tracer because the effect on the fetus is unknown. Sentinel lymph node biopsy with blue dye only may be offered to these patients. Pediatric patients may undergo sentinel lymph node biopsy, when clinically indicated, without untoward effects. Patients with a history of cosmetic dye allergy should not receive isosulfan blue.

While lymphoscintigraphy is extremely helpful in identifying the at-risk nodal basins in patients with melanoma of the head and neck, sentinel lymph node biopsy has been less successful in this region, with a localization rate of less than 95%, even with the combination of dye and radiocolloid. The procedure is technically challenging in this location.

Drainage patterns are quite variable and unpredictable. A greater number of sentinel lymph nodes, often from multiple basins, are identified in the head and neck compared with other sites, which increases surgical morbidity. The rate of sentinel lymph node positivity is less than that for melanomas at other sites, and the failure and false-negative rates are higher (approximately 4-fold). Despite this, safety and accuracy are still acceptable.

If multiple sentinel nodes are identified either in the neck or parotid region, many surgeons perform a superficial parotidectomy or modified neck dissection, rather than multiple biopsies through multiple incisions, in an area in which the lymph nodes usually are quite small and more difficult to identify and in which avoidance of injury to surrounding structures (eg, facial nerves, cranial nerves, major blood vessels) is of paramount importance. Sentinel lymph node biopsy in this location also relies heavily on the use of the combined technique, especially for primary tumors that are overlying the parotid gland and cannot be shielded to avoid interference with the handheld gamma probe. In this setting, the use of blue dye and, sometimes, repeated injections of dye, is important. This is also a consideration for any primary melanoma immediately overlying a regional nodal basin.

In some patients, shielding the primary site is not feasible because the sentinel lymph node is subjacent or close to the injection site. Initial wide excision (5-10 min after intraoperative injection of blue dye) of the primary tumor may be helpful, or the blue dye technique with in-continuity dissection of the lymphatics may be applied. When sentinel lymph node biopsy is not successful in these situations, consideration should be given to elective in-continuity lymph node dissection, if this has been discussed with the patient preoperatively, because the likelihood of relapse in the underlying nodal basin is a concern in patients with high-risk primaries.

Surgical therapy

The use of sentinel lymph node biopsy and selective lymphadenectomy in patients with malignant melanoma with clinically negative regional lymph node basins has been widely adopted. Current NCCN guidelines recommend this as a component of treatment for clinically node-negative melanoma patients with tumors thicker than or equal to 1 mm. With this approach, a complete regional lymph node dissection is performed only in patients with evidence of metastatic melanoma in the sentinel node(s). This technique is also being used for other skin cancers (eg, neuroendocrine carcinoma of the skin [Merkel cell carcinoma]) that have a propensity for regional lymphatic spread. Despite this, current compliance with these guidelines in the United States is only approximately 50%. The technical details of sentinel lymph node biopsy for malignant melanoma are described below.

Preoperative details

Sentinel lymph node biopsy with selective lymphadenectomy is a team effort and requires close collaboration by dermatologists, surgical oncologists, nuclear medicine physicians, and pathologists. Adjuvant therapy may also involve medical and radiation oncologists. A multidisciplinary programmatic approach provides optimal patient care.

In the nuclear medicine department, 2-16 hours before the operation, the patient is injected intradermally around the site of the primary tumor or biopsy scar with radiocolloid, usually with a dose of 0.5-0.8 mCi. The area is massaged for 2-5 minutes.

While a variety of radiocolloids have been used successfully, unfiltered ^99mTc sulfur colloid diffuses out of the sentinel lymph nodes (to second echelon lymph nodes) less rapidly than tracers with smaller particles. In the United States, ^99mTc-labeled albumin colloid and human serum albumin also may be used. In Australia, colloidal antimony sulfide is used, and in Europe, human albumin nanocolloid is used.

Lymphoscintigraphy is helpful in defining at-risk nodal basins, especially for truncal melanomas and melanomas of the head and neck. Lymphoscintigraphy may help define the number of sentinel lymph nodes by showing more than one afferent lymphatic channel leading from the primary tumor site to a regional nodal basin. It can also help define the location of the sentinel lymph node within the lymphatic basin and can identify in-transit lymph nodes that may contain metastatic disease. Lymphoscintigraphy demonstrates drainage to more than 1 nodal basin in 10-15% of patients and drainage to interval nodes in approximately 5%. The sentinel node is not always found in the closest nodal basin. Accurate lymphoscintigraphy helps identify all nodes, regardless of their location, receiving direct lymphatic drainage from a primary tumor site.

While not all surgeons advocate the use of preoperative lymphoscintigraphy in all melanoma patients, most agree that it is necessary to accurately identify the sentinel node(s) in patients with head and neck melanoma. Drainage to nodal basins not predicted by standard anatomic considerations is observed with lymphoscintigraphy in as many as 60% of head and neck and 30% of truncal primary melanomas. Dynamic scintigraphy can be performed most conveniently immediately after injection of radiocolloid in the nuclear medicine department on the morning of the operation. Usually, the sentinel lymph node(s) is identified within 30 minutes of injection. The site of each hot sentinel lymph node is tattooed on the patient's skin for identification in the operating room. Two-view lymphoscintigrams are obtained for the surgeon. Delayed 2-hour images may be taken.

Intraoperative details

After radioisotope is injected in the nuclear medicine suite and lymphoscintigraphy is performed, the patient is moved to the operating room. Vital blue dye (1-2 mL) is injected intradermally around the primary tumor or biopsy site after the patient is prepared and draped using sterile technique. Some clinicians use isosulfan blue dye (Lymphazurin 1%, Zenith Parenterals; Rosemont, Ill). The site is massaged gently for 5 minutes. A handheld gamma probe (eg, C-Trak probe, Care Wise Medical Products; Morgan Hill, Calif]) is used to identify hot spots in the identified regional lymph node basin or basins. If in-transit or interval nodes are identified on preoperative lymphoscintigrams, these should also be sought. Interval nodes contain metastatic disease as often as the conventional nodal basins do and may represent the only site of metastatic disease. The blue dye may also be seen coursing through the dermal lymphatics en route to the regional lymph node basin(s).

A small incision is made over the hot spot. A blue-stained afferent lymphatic vessel is sought, and a combination of this visual cue and the gamma probe leads to the identification of a hot and/or blue sentinel lymph node or nodes. Care should be taken to minimize flap placement because this may interrupt the afferent lymphatics and make sentinel node identification more difficult. More than 1 sentinel lymph node (with a separate draining afferent lymphatic vessel) is identified in more than 50% of patients.

After the sentinel lymph nodes are removed, the lymph node basin is scanned with the gamma probe for residual activity. Absent–to–low-level radioactivity confirms that the sentinel nodes have been removed. The ratio of activity of the sentinel lymph node to nonsentinel lymph nodes should be at least 3:1 in vivo. Generally, the ratio of activity of the ex vivo sentinel lymph node to nonsentinel lymph nodes should be greater than 10:1. At operation, a sentinel lymph node is any blue-stained node, any node with a blue-stained afferent lymphatic, or any node with greater than 10% of the radioactivity ex vivo of the hottest node.

The "10% rule" was generated from the Sunbelt Melanoma Trial experience and suggests that any lymph node with greater than 10% of the ex vivo radioactivity of the hottest lymph node should be removed. Ex vivo counts eliminate the contribution of shine-through from the primary site or from sentinel nodes remaining in the lymph node basin. This method is reportedly associated with a detection failure rate of approximately 2%. Any clinically suspicious, enlarged, firm, or pigmented lymph nodes should also be removed because tumor cells blocking afferent lymphatics may prevent uptake of radioactive tracer and/or blue dye into a tumor-containing sentinel lymph node.

If, despite these techniques, no sentinel lymph node is identified, either dissection of the lymph node basin or termination of the procedure and close clinical follow-up of the patient may be chosen. This decision should be based on a preoperative discussion with the patient and the metastatic risk associated with the primary tumor. Sentinel node identification rates can approach 99% when the procedure is performed by a trained multidisciplinary team.

Postoperative details

Processing the sentinel lymph node involves taking step-sections at multiple levels and performing immunohistochemical staining with S-100 protein and homatropine methylbromide (HMB-45) to identify micrometastatic disease. If any question exists about abnormal cells on these first sections, additional sections of the lymph node are taken. Immunohistochemistry identifies an additional 10-20% of patients with positive sentinel lymph nodes, in whom micrometastases are not seen on routine sections stained with hematoxylin and eosin (H&E). Melanoma antigen–recognizing T cells 1 (MART-1 or Melan A) antibody staining also may be performed to help identify occult micrometastatic disease in a sentinel lymph node. At least some of the increased rate of detection of micrometastatic disease is attributable to step-sectioning at multiple levels.

An international consensus group advocates a more formal and detailed sampling of the sentinel lymph node. Their approach involves bivalving the lymph node, fixing the 2 halves face down, and subsequently sectioning each half into 10 sections, which alternately are used for H&E staining, immunohistochemistry, and molecular staging. The Sydney Melanoma Unit performs 2 H&E sections (1 and 4) and 2 with S-100 and HMB-45 immunohistochemistry (2 and 3) on 4 sequential 5-mm thick sections taken from each block of 3-mm longitudinal slices of the sentinel lymph node. They cite a detection failure rate of less than 1% and an acceptable cost-to-benefit ratio with this method. Recommendations for optimal enhanced pathologic analysis vary, but all include step-sectioning and immunohistochemistry.

Another technique described to increase the accuracy of pathologic examination of the sentinel lymph node is carbon dye mapping of the microanatomy of the lymph node to direct the pathologist to the portion of the node most likely to contain metastatic disease. The sensitivity of intraoperative frozen section examination of the sentinel lymph node is disappointingly low (<50%), although false-positive results are almost never reported. Because of the risk of tissue loss and damage during the frozen section procedure, most melanoma centers eschew frozen sectioning and rely on permanent sections, except to confirm grossly suggestive metastatic disease.

The potential for understaging patients because of tissue loss after frozen sectioning is underscored by reports of lower than expected rates of sentinel node metastases from institutions where frozen section examinations are routinely performed. Intraoperative imprint cytology has been reported to have a sensitivity of approximately 40% for melanoma patients and better preserves the lymph node for permanent section evaluation.

Similar protocols are followed for the evaluation of sentinel lymph nodes from other skin cancers. For neuroendocrine carcinoma of the skin, the pancytokeratin antibody AE1/AE3, cytokeratin 20, and chromogranin A immunostaining on permanent sections helps identify micrometastatic disease in the sentinel lymph node.

Currently, in clinical studies, molecular staging is being applied to sentinel lymph nodes removed from melanoma patients in an effort to improve the sensitivity of detecting occult metastatic disease. This method uses reverse-transcriptase polymerase chain reaction (RT-PCR) to detect messenger RNA for markers frequently expressed by melanoma cells. The sensitivity of RT-PCR is estimated to be an order of magnitude greater than that of immunohistochemistry. The marker used most commonly is tyrosinase, the enzyme that governs tyrosine metabolism in pigment cells. RT-PCR can also be used to detect other melanoma surface antigens such as Gp-100, MART-1, melanoma-associated antigen 3, and melanoma inhibitory activity.

Studies suggest that the 2-year recurrence rate for patients with a histologically (including immunohistochemistry) negative and PCR-negative sentinel lymph node is 2-9%. The 2-year recurrence rate is 13-30% for patients with a histologically negative yet PCR-positive lymph node and 60-67% for patients with lymph nodes positive by both methods. These data suggest that lymph node metastases missed by pathologic assessment are clinically relevant. Other studies have not found molecular staging of sentinel lymph nodes to have prognostic significance. The ongoing Sunbelt Melanoma Trial and Florida Melanoma Trial both use this technology and should provide useful information on the clinical relevance of molecular staging.

Complete regional lymphadenectomy should be performed in all patients with positive sentinel lymph node results, even when the volume of disease is quite small, in the absence of participation in a randomized clinical trial. As yet, no method reliably predicts which patients will have residual metastatic disease in other nonsentinel lymph nodes in the regional basin. While, in most series, 70% of patients (range 58-92%) have no further disease identified, the pathologic examination after regional lymph node dissection is, of necessity, less rigorous than that used for evaluation of the sentinel lymph node; therefore, these numbers probably underestimate the true incidence of additional nodal disease.

Removal of a greater number of sentinel lymph nodes results in a lower proportion of positive nodes on completion lymphadenectomy. However, numerous studies have failed to show any reliable and reproducible way of prospectively identifying those patients at an acceptably low risk of harboring residual disease in the nodal basin so as to forgo completion lymphadenectomy. Population-based data analysis (National Cancer Institute's Surveillance, Epidemiology and End Results [SEER] database 1998 to 2001) shows that less than 70% of US melanoma patients with a positive sentinel lymph node receive a completion lymph node dissection. As melanoma remains a disease in which appropriate surgical treatment is of paramount importance (ie, because of the paucity of highly effective systemic therapy options), the consequences of inadequate treatment may be grave.

A complete axillary lymph node dissection should include all level I, II, and III nodes and should remove all lymph nodes and fatty and areolar tissue from within the anatomic boundaries of the axilla. Usually, these specimens include a minimum of 15-20 lymph nodes. This is not the operation commonly performed for breast cancer staging and underscores the importance of including a trained surgical oncologist with experience in the treatment of melanoma as a member of the multidisciplinary team.

The appropriate extent of groin dissection remains controversial. Isolated pelvic, obturator, or iliac nodal disease may be seen without involvement of (superficial) inguinal nodes, but this is uncommon. After a positive inguinal sentinel lymph biopsy result, the approach may be to perform only a superficial groin dissection at all times, a radical groin dissection at all times, or the deep groin dissection selectively, depending on the number of involved superficial nodes, the status of the node of Cloquet, or the site of the primary tumor (extremity vs trunk).

Two studies, the Multicenter Sentinel Lymphadenectomy Trial (MSLT) II and part II of the Florida Melanoma Trial are currently enrolling subjects after a positive sentinel lymph node biopsy result to be randomized to completion lymphadenectomy or no further surgical treatment. The MSLT-II aims to accrue 4200 subjects with primary melanomas greater or equal to 1.2 mm (or Clark level IV/V or ulceration) to undergo lymphatic mapping (with blue dye, carbon dye, and radiocolloid) with sentinel lymphadenectomy. Those with a positive sentinel lymph node (by H&E, immunohistochemistry, or RT-PCR) will be randomized to completion lymph node dissection or observation (including follow-up nodal ultrasound) with therapeutic lymph node dissection for relapse.

Part II of the Florida Melanoma Trial seeks to randomize subjects with positive sentinel nodes by H&E histology, immunohistochemistry, or PCR to completion lymph node dissection plus adjuvant therapy with interferon alfa-2b or interferon alfa-2b alone. The study will obtain candidates for randomization from a planned accrual of 3200 clinical stage I and II patients with melanomas thicker than 0.75 mm undergoing lymphoscintigraphy, lymphatic mapping, and sentinel lymph node biopsy from 10 institutions (part I of the study).

In general, patients who undergo sentinel lymph node biopsy alone require no special postoperative care. They may be discharged the day of the procedure, depending on the nature of the treatment of the primary melanoma. Instructions and written materials on lymphedema prevention and precautions should be provided to patients. Extremity elevation and ACE wraps may be used to prevent lymphedema in the initial treatment of patients who undergo lower extremity sentinel lymph node biopsy. These patients are usually fitted with a compression stocking 4-6 weeks postoperatively.

Systemic treatment with high-dose interferon alfa-2b or participation in a clinical trial is generally offered to stage III patients. Adjuvant radiotherapy is recommended for most patients with multiple cervical lymph node metastases and for those patients with bulky nodal metastases or extracapsular extension at any site.

Follow-up

Appropriate follow-up monitoring of patients with intermediate-thickness and deep primary cutaneous melanoma after sentinel lymph node biopsy, and treatment in general, remains controversial. Advantages to a regular follow-up program include a detailed history and physical examination (with total skin and regional lymph node examinations), with particular focus on the site of the primary melanoma and regional lymph node basin(s). Follow-up monitoring may detect second primary melanomas (approximately 5% of patients at 5 y) and recurrent disease at an early stage, when it may be treated more easily. Follow-up care also may include psychosocial support, identification of familial melanoma, and ongoing patient education.

Typically, examinations are performed at 3- to 6-month intervals for 5 years and annually thereafter. Usually, chest radiography and liver function tests with a lactate dehydrogenase level are performed annually, although most clinicians recognize that these tests are insensitive. Lifelong surveillance is recommended, not only to detect new primary skin cancers, but also to detect late recurrences (>10 y post diagnosis). These recommendations are typical for stage I or II melanomas thicker than 1 mm or for Clark level IV or V melanomas and for patients with stage III melanoma. Similar guidelines are used for follow-up monitoring of patients with neuroendocrine carcinoma of the skin and other types of skin cancer with some propensity for local, regional, and distant recurrence.

Although sentinel lymph node dissection with selective lymphadenectomy is less morbid than elective lymph node dissection, as with any invasive procedure, complications do occur. In the Sunbelt Melanoma Trial, the overall complication rate was less than 5% for sentinel lymph node biopsy alone and 23% for sentinel lymph node biopsy with completion lymph node dissection for metastatic disease. The mortality rate was 0% for both procedures. Complications occur more frequently in patients with comorbid illness or habits such as cardiac disease, obesity, diabetes mellitus, and cigarette smoking. The complication rate has also been reported to increase with the number of sentinel nodes removed.

Immediate complications of the procedure include failure to identify a sentinel lymph node (generally, <5%), anaphylaxis or other allergic reactions to the intradermal injection of blue dye ( <1%), and bleeding. The immediate false-negative rate is defined as the proportion of nodal basins with positive nonsentinel lymph node results after negative results are obtained from sentinel lymph node biopsy immediately followed by elective completion lymph node dissection. In published series that included initial cases early on in the learning curve, the immediate false-negative rate ranged from 4.7-8.3%, with an associated accuracy of 98-99%. Further studies of this nature are unlikely, given the acceptance of sentinel lymph node biopsy with selective lymph node dissection.

Short-term postoperative complications of the procedure include hematoma, wound infection, seroma, and flap necrosis. In the Sunbelt Melanoma Trial, hematoma or seroma (2%) and wound infection (1%) were the most common complications of sentinel lymph node biopsy.

Long-term postoperative sequelae may include persistent blue discoloration of the skin at the injection site (for >30 d in <10% of patients), lymphatic fistulae, lymphocele, lymphedema (generally <2% and 0.66% in 1 large trial), and neurologic complications including transient or persistent neurapraxia, cutaneous anesthesia, paresthesias, and neuropathy. Sentinel lymph node biopsy does not increase the risk of in-transit metastases.

Initial reports on the risk of locoregional recurrence were with fairly short-term follow-up ranging from 13-48 months in 10 published series. The risk of isolated nodal relapse in the mapped basin after negative results from sentinel lymph node biopsy was stated to be from less than 1% to 6%, while the locoregional relapse rate ranged from 5-10%. These data included varying numbers of patients with thin or otherwise low-risk melanomas who were expected to have minimal risk of relapse.

Contemporary series of sentinel lymph node–negative melanoma patients include 5 series published from 2000-2005 with greater than or equal to 500 such patients each followed for a median of 16-42 months with a failure rate (nodal recurrence in previously mapped basin in the absence of new in-transit or systemic disease or first recurrence in any regional nodal basin) of 1.5-6%, corresponding to a false-negative rate (false-negative cases divided by true-positive plus false-negative cases) of 7-24%.

Six series of sentinel node–negative patients followed for a median of greater than or equal to 36 months (range, 36-72 mo median follow-up) and published from 1999-2005 demonstrate a failure rate of 1.5-4.8% and a false-negative rate of 7-21%. In the largest single series (836 sentinel node–negative patients) followed for more than 36 months (median 42 mo) published as of January 2006, the failure rate was 2.6% and the false-negative rate was 13.2%. Isolated nodal recurrence after complete regional lymph node dissection (by a trained surgical oncologist) occurs in 1-3% of patients.

Potential technical reasons for failure include errors in surgical technique; failure of nuclear medicine mapping; alterations in lymphatic drainage by inflammation, infection, or previous surgery; and errors in the pathologic examination of a correctly identified true sentinel node. Reexamination of negative findings from sentinel lymph nodes from patients with regional nodal relapse using careful step-sectioning and immunohistochemistry has been demonstrated to detect micrometastatic disease in 40-80% of patients. Conversely, nodal relapse may result from newly developed nodal metastases arising from clinically occult or newly apparent local or in-transit disease. Most (30-60%) relapses in sentinel node–negative patients are distant metastasis without any evidence of local, in-transit, or regional disease.

The now-widespread use of sentinel lymph node biopsy to more accurately stage melanoma has provided valuable information toward a better understanding of the natural history of malignant melanoma. Significant stage migration has been seen as more patients previously classified as node-negative are reclassified as having stage III disease.

The latest AJCC staging system for melanoma, adopted officially in 2003, arose from the work of the AJCC Melanoma Staging Committee and was developed after evaluation of 17,600 patients from merged prospective databases from 13 cancer centers. The importance of microstaging using sentinel lymph node biopsy with selective lymph node dissection is emphasized by its inclusion in the pathological N staging of melanoma patients. From this data set, 5-year survival rates for stage III patients stratified by number and type (microscopic, ie, identified by sentinel lymph node biopsy or elective lymph node dissection, without extracapsular extension, and clinically and/or radiologically occult versus macroscopic) and primary tumor ulceration range from 69% (nonulcerated primary tumor, one microscopic positive lymph node) to 13% (ulcerated primary tumor, > 3 macroscopic positive lymph nodes). This compares favorably with historic studies.

In a large series of patients who underwent regional lymph node dissection without sentinel lymph node biopsy, 5-year survival estimates ranged from 46-60% for 1 lymph node with positive results, 33-54% for 2-3 lymph nodes with positive results, and 21-44% for 4 or more lymph nodes with positive results, depending on the extent and completeness of the regional lymph node dissection. In other series, the 10-year survival rate is estimated to be as high as 60-70% for patients with nonpalpable micrometastatic disease in just 1 lymph node, while the 10-year survival rate for patients with 2-3 occultly positive lymph nodes is approximately the same as in patients with 1 macroscopically positive lymph node.

A recent population-based study of 41,417 patients from the National Cancer Institute's SEER cancer registry validated the AJCC melanoma staging system, but it revealed more favorable survival rates. In this study, the 5-year survival rate for N2b (2-3 macroscopically positive nodes) with a nonulcerated primary tumor was 50% and dropped to 27% for patients with more than 3 macroscopically positive nodes with an ulcerated primary tumor. The SEER data for microscopically node–positive patients are, as yet, immature, but 2-year survival for N1a and N2a patients ranged from 75-90%. Further data analysis with long-term follow-up monitoring of patients undergoing selective lymph node dissection after sentinel lymph node biopsy with positive results and data from ongoing clinical trials undoubtedly will provide further prognostic information over the next few years.

Interim results of the MSLT I trial presented at 2 international meetings in 2005 show that while overall survival for intermediate-thickness patients randomized to wide local excision and sentinel lymph node biopsy with selective lymph node dissection versus observation is not yet statistically significant (93% vs 90% at 5 y), disease-free survival was significantly better for patients undergoing sentinel lymph node biopsy with selective lymph node dissection (79% vs 73%, P <.05).

In addition, 5-year overall survival was significantly better for patients with positive sentinel lymph nodes who underwent immediate completion lymph node dissection versus those who underwent therapeutic lymph node dissection for recurrence after wide excision alone (71% vs 53%, P = .0034). Patients in the latter group had a greater number of involved lymph nodes (3.4 vs 1.6 for the sentinel lymph node–positive group) and 27% had N3 disease. In addition, sentinel lymph node status had prognostic significance, with 83% 7-year survival for sentinel node–negative patients versus 66% for sentinel node–positive patients.

Overall survival was identical for patients with a negative sentinel lymph node biopsy result and patients treated by wide excision and observation without recurrence. The proportion of sentinel lymph node–positive patients was 19.8%, and the proportion with nodal recurrence after wide excision alone was 20.3% at 7 years, further validating the sentinel lymph node concept. The data analysis includes the false-negative sentinel node patients. Sentinel lymph node biopsy did not increase the risk of developing in-transit disease.

The current standard of care is to offer adjuvant treatment with high-dose interferon alfa-2b to stage III melanoma patients or to offer them participation in a clinical trial. The Eastern Cooperative Oncology Group (ECOG) Trial 1684 compared high-dose adjuvant interferon alfa-2b therapy for 1 year with observation in patients with lymph node–positive results (89%) or thick primary (>4 mm, 11%) malignant melanoma. A survival benefit was seen in the treated patients. This regimen subsequently received US Food and Drug Administration approval as adjuvant therapy for high-risk patients with melanoma.

Subsequently, a pooled analysis of ECOG trials of adjuvant high-dose interferon alfa-2b for stage IIB and III melanoma patients has shown consistent improvement in disease-free survival but minimal improvement in overall survival in only 2 of 4 studies.

Further analysis of the data with longer-term follow-up observation is anticipated. Identification of patients who will benefit from adjuvant interferon alfa-2b therapy remains an active area of investigation. Proper stratification of patients within clinical trials, using accurate staging of disease after sentinel lymph node biopsy with selective lymphadenectomy, should help determine which patients derive the greatest benefit from adjuvant treatment, regardless of whether they receive interferon alfa-2b or melanoma vaccines, with or without additional biologic response modifiers or chemotherapy.

While several studies suggest a benefit to early eradication of clinically occult regional lymph node metastases from malignant melanoma, no proven therapeutic benefit for sentinel lymph node biopsy with selective lymphadenectomy, in terms of overall survival for all such treated patients, has been documented. In addition, while the short-term risk of regional recurrence after negative biopsy results from a sentinel lymph node appears to be low, long-term data are lacking. Two randomized clinical trials, MSLT I and the Sunbelt Melanoma Trial, may resolve these issues within the next few years.

The Sunbelt Melanoma Trial will also examine the usefulness of RT-PCR detection of tyrosinase and 1 of 3 other markers in the sentinel lymph node as prognostic markers, including treatment stratification for patients with RT-PCR–positive results in whom lymph node biopsy results appear negative after routine histology and immunohistochemistry. Two newer trials, MSLT II and part II of the Florida Melanoma Trial (mentioned in greater detail above) are currently enrolling patients after a positive sentinel lymph node biopsy result, including those found to be node positive by PCR only, to be randomized to completion lymphadenectomy or no further surgical treatment. The results of these trials should be decisive in determining the proper role of lymphatic mapping and sentinel lymphadenectomy and the value of molecular staging of sentinel lymph nodes.

In addition to the questions that will be answered by the 4 trials referenced above, other areas of investigation are ongoing in the area of melanoma progression, staging, and treatment.

High-frequency ultrasonography, with FNA of suggestive lymph nodes, is being investigated as a tool to identify or exclude nodal disease in melanoma patients. To date, the sensitivity and positive predictive value is low, but these may improve with technological advances. Ultrasonography is also being investigated as a tool to identify sentinel lymph nodes and to follow patients postoperatively for the development of new nodal disease. Fluorodeoxyglucose positron-emission tomography scanning and positron-emission tomography scanning are being used increasingly in melanoma patients, but these are generally insensitive for detecting early nodal disease. False-positive results have been reported. Further technological refinements may decrease the size of the current detection limit of approximately 5 mm.

Proton magnetic resonance spectroscopy of FNA samples of sentinel lymph nodes has recently been reported. Evaluation of sentinel lymph nodes removed surgically had a sensitivity of 88%, specificity of 90%, and accuracy of 89% in predicting sentinel lymph node status. These investigators propose a nonsurgical sentinel lymph node evaluation using ultrasound-guided FNA with this technique, without the need for histopathological evaluation.

Biologic and genetic alterations in primary melanomas and lymph node metastases continue to be studied. B-raf and N-ras mutations; differential integrin expression; and the roles of other angiogenesis, cell motility, and invasion genes are under active investigation. This may prove to have clinical relevance (eg, specific antibody therapy) in the future. Preoperative molecular characterization of melanomas may lead to even more minimally invasive or noninvasive staging and treatment in selected patients.

The use of sentinel lymph node biopsy with selective lymphadenectomy has increased the identification rate of micrometastatic disease and decreased the morbidity of proper treatment of melanoma patients. Sentinel lymph node status has been shown repeatedly to be the most powerful indicator of prognosis. Sentinel lymph node biopsy identifies patients for adjuvant therapy and stratifies patients into more homogeneous groups for inclusion in clinical trials. Sentinel lymph node biopsy identifies patients who need early therapeutic lymph node dissection.

Patients who undergo sentinel lymph node biopsy with selective lymph node dissection have an improved disease free-survival rate and improved regional disease control compared with those who undergo wide local excision of the primary tumor and observation alone. Those clinically node–negative melanoma patients with occult nodal disease detected and treated at the time of initial presentation have an improved overall survival rate compared with those patients who undergo delayed therapeutic lymph node dissection only when disease becomes clinically evident. This technique may also result in future refinements of the staging system for malignant melanoma and greater understanding of the natural history and progression of melanoma. It also may be proven to result in an overall survival benefit for patients undergoing the procedure.