Excerpt from Peritoneal Cancer

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Background

The peritoneum is a serous lining of mesothelial cells with rich vascular and lymphatic capillary network that covers the abdominal and pelvic walls and organs. Peritoneal neoplasia can originate de novo from the peritoneal tissues (primary) or invade or metastasize into the peritoneum from adjacent or remote organs (secondary).

A number of primary cancers have been described to originate from the peritoneum, some of which have been implicated in many cases of carcinomas of unknown primary origin. Ovarian cancer arising in women several years after bilateral oophorectomy is believed to be one of these primary peritoneal cancers. Other described primary peritoneal cancers and tumors include malignant mesothelioma, benign papillary mesothelioma, desmoplastic small round cell tumors, peritoneal angiosarcoma, leiomyomatosis peritonealis disseminata (LPD), and peritoneal hemangiomatosis.

Pathophysiology

The peritoneal cavity, enclosed by visceral and parietal peritonea, is the largest potential space in the body. Any pathologic process involving the peritoneal cavity can easily disseminate throughout this space by means of unrestricted movement of fluid and cells.

Primary malignant diseases arising from the peritoneal cavity include malignant mesothelioma, cystic mesothelioma, primary peritoneal carcinoma, and desmoplastic small round cell tumor. 

Malignant mesothelioma

Malignant peritoneal mesothelioma is a rare but aggressive tumor derived from the peritoneal mesothelium. Although most mesotheliomas involve the pleural surface, 20-30% arise from the peritoneum and are associated with asbestos exposure and abdominal therapeutic radiation. Association of malignant peritoneal mesothelioma and asbestos exposure has been reported to be as high as 83%.

Mesotheliomas are composed of strands of connective tissue covered by cells that react positively to periodic acid-Schiff staining in the cytoplasm. These cells grow in multiple layers, forming papillary or tubular formations. Histologically malignant mesothelioma is classified into epithelial, sarcomatoid, and mixed. Clinical features of malignant mesothelioma include abdominal pain, abdominal or pelvic masses, and thrombocytosis with ascites being the major factor in the disease morbidity and mortality. Rarely, the tumor tends to spread into the pleural space.

On CT scan, this neoplasm can appear as peritoneum-based masses or abdominal ascites with associated nodular or diffuse peritoneal thickening.

This locally aggressive disease is difficult to treat or palliate and, commonly, treatment regimens combine aggressive cytoreductive surgery with intraperitoneal chemotherapy.

Thorough cytoreductive surgery is the cornerstone of current treatment, while hyperthermic intraoperative intraperitoneal chemotherapy (HIIC) is a promising strategy in suitable patients.

Cystic mesothelioma

Cystic mesothelioma is a rare intermediate-grade tumor with a predilection for surfaces of the pelvis. Typically, these lesions consist of multiple grapelike clusters of mesothelium-lined cysts separated by fibrous tissue. The nomenclature for this entity is confusing, and several synonyms (eg, multilocular peritoneal inclusion cyst, cystic mesothelioma) are used interchangeably in the literature.

This rare tumor commonly occurs in young to middle-aged women and typically presents with abdominal pain, tenderness, or distension.

Radiologic tests demonstrate thin-walled cysts containing watery secretions, easily seen on ultrasound, CT scan, and MRI.

Some authors reported effective intraperitoneal chemotherapy, but no clinical study is available about long-term outcome. The short-term prognosis is favorable, although it can recur in 25–50% of cases.

The differential diagnoses include lymphangioma, mesenteric-omental cysts, ovarian cystadenoma and cystadenocarcinoma, cystic teratoma, pseudomyxoma peritonei, cystic smooth muscle tumors, visceral cysts, and endometriosis.

Primary peritoneal carcinoma

Primary peritoneal carcinoma (ie, serous surface papillary carcinoma) arises primarily from peritoneal cells. The mesothelium of the peritoneum and the germinal epithelium of the ovary arise from the same embryologic origin; therefore, the peritoneum may retain the multipotentiality allowing the development of a primary carcinoma.

This rare malignancy predominantly affects postmenopausal women typically with multicentric peritoneal and omental involvement. It resembles papillary serous ovarian carcinoma in pathological and clinical aspects. This malignancy is differentiated from its ovarian counterpart by the fact that it involves the extraovarian peritoneum significantly and the ovarian surface minimally or not at all. Extensive calcification or omental caking is present in many cases and is a useful CT finding to exclude mesothelioma. The absence of an ovarian mass is critical for excluding metastatic papillary serous ovarian carcinoma, which otherwise has a similar CT appearance.

Treatment of this malignancy is very similar to that of epithelial ovarian cancer, which includes combination chemotherapy after optimal cytoreductive surgery.

Desmoplastic small round cell tumor

This tumor is a highly aggressive malignancy that has recently been described. It involves the peritoneal cavity in most cases. Unlike the other primary peritoneal neoplasms, desmoplastic small round cell tumor (DSRCT) most often affects young adults. This malignancy extensively and rapidly invades the peritoneal surfaces with hematogenous metastasis to the liver, lungs, and lymph nodes.

Cytologically, DSRCT is a highly cellular tumor composed of small round cells with granular chromatin, nuclear molding, and inconspicuous nucleoli that are arranged singly and in clusters. This tumor exhibits a unique immunohistochemical profile, characterized by coexpression of epithelial (keratin and epithelial membrane antigen), neural (neuron-specific enolase and CD56), mesenchymal (vimentin), and myogenic (desmin) markers. The reciprocal chromosomal translocation t (11; 22)(p13; q12) is also specific for DSRCT.

Radiological investigation shows multiple rounded peritoneal masses with or without ascites. The omentum and paravesical regions are often involved.

The recommended treatment is a combination of multiagent chemotherapy with adjuvant surgery and radiation. The overall survival for people with this disease is poor despite aggressive treatment.

Other neoplasms

In addition to the above-mentioned primary peritoneal malignancies arising from the peritoneal lining, various types of neoplasms may develop from mesenchymal and lymphatic tissues of the abdominal and pelvic cavities. This includes different forms of sarcomas, histiocytoma, gastrointestinal stromal tumors (GIST), and lymphoproliferative malignancies. Moreover, the differential of peritoneal malignancies includes many benign tumors derived from lymphatic, vascular, neuromuscular, or fatty tissues.

Frequency

United States

All of the primary peritoneal cancers are rare. Primary peritoneal carcinoma is very uncommon. Peritoneal mesotheliomas are also rare, with 2 cases per 1 million population reported each year. However, the incidence appears to be increasing. Based on the prior use of asbestos, more than 8 million people in the United States were exposed and at risk. Benign cystic peritoneal mesotheliomas are rare.

Mortality/Morbidity

• Survival is poor for patients with primary peritoneal carcinoma, with 100% mortality; the median survival reported is 12-25 months, even with extensive surgery and chemotherapy.
• Benign cystic peritoneal mesotheliomas are associated with prolonged survival despite bulky disease.
• Desmoplastic small round cell tumors are associated with a reported median survival of 17 months.

Sex

• Primary peritoneal carcinoma is a rare tumor that occurs almost exclusively in women.
• Malignant mesotheliomas show extreme male predominance (93% in one series).

Age

• Patients with primary peritoneal carcinoma are older than patients with epithelial ovarian cancers.
• Desmoplastic small round cell tumors occur in adolescent persons and young men.
• Benign cystic peritoneal mesotheliomas are rare and are found predominantly in younger women.
• Most cases of leiomyomatosis peritonealis disseminata have been discovered in reproductive-aged women (mean age 37 y), in young pregnant women, and in women who have hormonal excess for any other reason. In most reported cases, nodules either regress or exhibit growth once the hormonal stimulation has been removed.

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