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Dermatology > BENIGN NEOPLASMS
Proliferating Pilar Tumor
Article Last Updated: Mar 10, 2008
AUTHOR AND EDITOR INFORMATION
Section 1 of 10  
Author: Amor Khachemoune, MD, CWS, Clinical Instructor, Mohs Micrographic Surgery, Department of Dermatology, State University of New York Downstate Medical Center; Consulting Staff, Department of Dermatology, Veterans Affairs Medical Center of Brooklyn
Amor Khachemoune is a member of the following medical societies: American Academy of Dermatology, American Academy of Wound Management, American College of Mohs Micrographic Surgery and Cutaneous Oncology, American Medical Association, American Society for Dermatologic Surgery, and American Society for Laser Medicine and Surgery
Coauthor(s):
Steve A McClain, MD, Clinical Associate Professor, Department of Pathology, State University of New York at Stony Brook; Medical Director, Founder and Owner, McClain Laboratories LLC;
Daniel Mark Siegel, MD, MS, Director, Procedural Dermatology Fellowship Program, Clinical Professor of Dermatology, Department of Dermatology, State University of New York Downstate;
Rashid M Rashid, MD, PhD, Resident, Department of Dermatology, MD Anderson Cancer Center, University of Texas;
Kimberly Silvers, MD, PhD, Staff Physician, Section of Dermatology, Guthrie Clinic
Editors: R Stan Taylor, MD, Professor of Dermatology, University of Texas Southwestern Medical School; Director of Skin Surgery and Oncology Clinic, Department of Dermatology, University of Texas Southwestern Medical Center; Richard P Vinson, MD, Assistant Clinical Professor, Department of Dermatology, Texas Tech University School of Medicine; Consulting Staff, Mountain View Dermatology, PA; John G Albertini, MD, Consulting Staff, Dermatologic Surgery, The Skin Surgery Center; Glen H Crawford, MD, Assistant Clinical Professor, Department of Dermatology, University of Pennsylvania School of Medicine; Chief, Division of Dermatology, The Pennsylvania Hospital; William D James, MD, Paul R Gross Professor of Dermatology, University of Pennsylvania School of Medicine; Vice-Chair, Program Director, Department of Dermatology, University of Pennsylvania Health System
Author and Editor Disclosure
Synonyms and related keywords:
proliferating trichilemmal cyst, pilar cyst, proliferating trichilemmal tumor, isthmus-catagen cyst
Background
A proliferating pilar tumor (PPT) is a rare neoplasm arising from the isthmus region of the outer root sheath of the hair follicle. It was first described by Wilson-Jones1 as a proliferating epidermoid cyst in 1966. PPT was then distinguished from proliferating epidermoid cysts in 1995.2 It occurs most commonly on the scalp in women older than 50 years.3 Most tumors arise within a preexisting pilar cyst. Even though they usually are benign in nature, malignant transformation with local invasion and metastasis has been described.4, 5, 6 A tentative stratification of PPTs into groups as benign, low-grade malignancy, and high-grade malignancy has been introduced. They may be inherited in an autosomal-dominant mode, linked to chromosome 3. See Pilar Cyst for more information.
Pathophysiology
A PPT usually arises in the setting of single or multiple pilar cysts. An asymptomatic nodule is often present for months to years before a rapid increase occurs in the size of the lesion. This is thought to signal neoplastic transformation of the cyst, with progression into a PPT. The underlying stimulus for this transformation is not known, but it has been hypothesized to be secondary to trauma, irritation, or chronic inflammation. In a review of 76 cases of PPTs seen in consultation from 1989-2000, Ye et al7 proposed a distinction between benign and malignant variants. The authors also proposed histologic criteria that could predict behavior.
Frequency
United States
These tumors are rare. Only a few cases of malignant transformation have been reported.
Mortality/Morbidity
The lesions are usually painless. Exophytic growth with ulceration and foul-smelling discharge may occur. Some lesions may grow very large and cause pressure necrosis on underlying tissues, especially on the scalp. Local recurrence following excision and/or metastasis has been reported in rare instances in which malignancy has occurred.
Sex
These tumors occur more commonly in females than in males.
Age
PPTs are most common in older individuals aged 50-75 years, although they have been reported in individuals aged 20-30 years.
History
- Patients usually report a slowly or rapidly enlarging nodule.
- Patients may give a history of recent trauma to the site.
- The nodule may have been present for months to years without symptoms.
Physical
- Lesions usually are single, firm-to-soft, painless nodules.
- The size may range from 1-10 cm, although lesions as large as 25 cm have been reported.
- Inflammation, ulceration, bleeding, and/or yellowish discharge may occur.
- The most common (90%) location is the scalp.
- Other reported sites include back, chest, axilla, groin, gluteal region,8 thigh, vulva,9 and face.
Causes
A spectrum of transformation is hypothesized, which begins with a benign pilar cyst, proceeding to a PPT, and then to a malignant PPT. The stimulus for changes in these lesions is currently unknown, although trauma, inflammation, and irritation may play roles.
Cylindroma
Dermoid Cyst
Squamous Cell Carcinoma
Imaging Studies
- Imaging studies are not usually indicated, but they may show a lobulated cystic mass, coarse calcification, or ringlike mineralization.
- The best modality to determine bony invasion or erosion is CT scanning.10 However, for deeper tissue invasion, MRI is best.
- On the other hand, because some subcutaneous tumors located in the midline of the body may have connections to the central nervous system (eg, scalp cavernous angioma, which may be part of the symptom complex known as sinus pericranii), imaging tumors in this location prior to removal should be considered. CT scanning and MRI are helpful in determining if such connections are present.
Procedures
- Performing an excisional biopsy is recommended. Send as much of the lesion as possible for pathologic evaluation. Ideally, the entire lesion should be excised and submitted at the time of the biopsy.
Histologic Findings
The neoplasm is well circumscribed, with islands of squamous epithelium undergoing trichilemmal keratinization. Horn pearls or squamous eddies may be present, as may foci of calcification and glycogen-rich clear cells.
The epithelial cells lining the cyst lack intercellular bridges. The peripheral layers palisade, while the deeper layer cells are swollen. Anti-CK 5/6 may also stain strongly positive in this neoplasm. This is a monoclonal antibody that recognizes high molecular weight keratin intermediate filaments. An increase in staining of nucleolar organizer regions, an indicator of proliferation, has also been proposed as an adjunct to differentiate benign and malignant proliferating trichilemmal tumors.11 Ye et al7 proposed a stratification of PPTs into the following 3 groups:
- Group 1 - Circumscribed silhouettes with "pushing" margins; modest nuclear atypia; and an absence of pathologic mitoses, necrosis, and invasion of nerves or vessels
- Group 2 - Similar to group 1 but manifest as irregular, locally invasive silhouettes with involvement of the deep dermis and subcutis
- Group 3 - Invasive growth patterns, marked nuclear atypia, pathologic mitotic forms, and geographic necrosis, with or without involvement of nerves or vascular structures.
Group 1 may be regarded as benign, group 2 as having the potential for locally aggressive growth, and group 3 as also having metastatic potential. The latter 2 categories might be equated with low and high grades of malignancy among PPTs of the skin.
The cyst cavity contains amorphous eosinophilic keratin. The content is commonly calcified.
Surgical Care
Complete excision with a margin of normal tissue is recommended. No consensus has been reached regarding the margin size of normal tissue.
Further Outpatient Care
- Monitor the patient for local recurrence and periodically examine the lymph nodes to rule out metastasis. No recommendations exist for the interval or length of follow-up.
- Screening for PPT is suggested in patients with keratitis-ichthyosis-deafness (KID) syndrome.12
Prognosis
- The prognosis is excellent with complete excision. Local recurrence and metastasis are extremely rare in benign cases. However, in proven malignant cases, metastasis has been suggested to occur in 30% of cases.
Patient Education
Medical/Legal Pitfalls
- The sudden change in size of a preexisting cyst should be suspect and warrants excisional biopsy.
- Biopsy material should be read by a competent dermatopathologist.
- Ample sampling of the tissue should be obtained to assess focal malignant change.
- Some areas may be mistaken for squamous cell carcinoma3 and thus lead to more aggressive, yet unnecessary, surgical management.
| Media file 1:
Proliferating trichilemmal cystic neoplasm. Well-circumscribed neoplasm with central cornified cells (2X). Courtesy of Steve A. McClain, MD. |
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| Media file 2:
Proliferating trichilemmal cystic neoplasm (20X). Courtesy of Steve A. McClain, MD. |
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Media type: Photo
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| Media file 3:
Proliferating trichilemmal cystic neoplasm (400X). Note the pleomorphism of keratinocytes and mitotic figures. Courtesy of Steve A. McClain, MD. |
 | View Full Size Image | |
Media type: Photo
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- Wilson-Jones E. Proliferating epidermoid cysts. Arch Dermatol. 1966;94:11.
- Sau P, Graham JH, Helwig EB. Proliferating epithelial cysts. Clinicopathological analysis of 96 cases. J Cutan Pathol. Oct 1995;22(5):394-406. [Medline].
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Proliferating Pilar Tumor excerpt Article Last Updated: Mar 10, 2008
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