Peritoneal tumors are more common in females than in males, particularly primary peritoneal tumors. These tumors exhibit diverse pathological types, with epithelial tumors derived from the Müllerian ducts being managed and treated in accordance with the principles for epithelial ovarian tumors.
Pathology
According to the 2020 WHO Histological Classification of Tumors of the Female Reproductive System, primary peritoneal tumors are categorized into four major groups: mesothelial tumors, epithelial tumors, peritoneal-specific mesenchymal tumors, and tumor-like lesions. In addition, because of its unique anatomical location, the peritoneum is frequently involved in metastatic tumors.
Mesothelial Tumors of the Peritoneum
These tumors originate from mesothelial cells of the peritoneum and are predominantly malignant. Benign mesothelial tumors are rare. Malignant mesothelial tumors are usually referred to as mesotheliomas, as the latter inherently possess malignant characteristics. Peritoneal mesotheliomas account for approximately 20% of all mesotheliomas and are highly aggressive. Their etiology remains unclear but may be associated with exposure to certain minerals (particularly asbestos), chronic inflammatory stimulation, viral infections, and genetic factors.
Epithelial Tumors of the Peritoneum
These tumors arise from the epithelial cells of the Müllerian ducts, with their exact pathogenesis still being debated. Some researchers have proposed the concept of the secondary Müllerian system, suggesting that the embryonic coelomic epithelium, which gives rise to both ovarian and peritoneal epithelium, retains the potential for Müllerian differentiation and can give rise to tumors under certain stimuli. Consequently, peritoneal carcinomas closely resemble epithelial ovarian carcinomas. Recent advances in pathology and molecular genetics increasingly suggest that serous tubal intraepithelial carcinoma (STIC) of the fallopian tube epithelium may represent a common origin for both primary peritoneal carcinoma and high-grade serous ovarian carcinoma.
Metastatic Peritoneal Tumors
Advanced gastrointestinal tumors and serous ovarian carcinomas commonly involve peritoneal metastases. Immunohistochemistry is often used to distinguish the former. However, distinguishing primary peritoneal carcinoma from peritoneal metastases of serous ovarian carcinoma is challenging due to similarities in histological morphology and immunophenotype. The diagnostic criteria proposed by the Gynecologic Oncology Group (GOG) are commonly employed for differentiation. These criteria include:
- Normal-sized ovaries or ovarian enlargement due to benign conditions.
- Extraovarian disease that is more extensive than surface involvement of the ovaries.
- Microscopically, no tumor cell infiltration in the ovaries, tumor cells confined to the ovarian surface with no cortical involvement, or tumor involvement of the ovarian capsule and cortex but measuring no greater than 5 mm × 5 mm.
As treatment principles for serous ovarian carcinoma and primary peritoneal serous carcinoma are similar, cases in which the primary site cannot be determined are often classified clinically as "tumors of unknown primary origin."
Diagnosis
Benign peritoneal tumors are rare, often asymptomatic, and difficult to detect through imaging. They are frequently discovered incidentally during unrelated abdominal surgeries. Advanced malignant peritoneal tumors may present with clinical features such as abdominal distension, ascites, and abdominal masses, with some patients exhibiting signs of cachexia. An elevated serum CA125 level serves as an important diagnostic indicator for epithelial malignancies of the peritoneum. Cytology of ascitic fluid can also aid in the diagnosis, although histopathological evaluation remains the definitive method for confirmation.
Treatment
Surgical resection is the preferred treatment for benign peritoneal tumors. The management of malignant peritoneal tumors is determined by their pathological diagnosis. For instance, primary serous peritoneal carcinoma is treated following the same principles as serous ovarian carcinoma. Initial treatment for malignant peritoneal mesothelioma typically involves extensive cytoreductive surgery combined with hyperthermic intraperitoneal chemotherapy (HIPEC). Cisplatin combined with pemetrexed is the first-line chemotherapy regimen for malignant peritoneal mesothelioma, with CTLA-4 and PD-1 antibodies providing additional therapeutic options. Management of metastatic peritoneal tumors depends on the location of the primary tumor and its treatment protocol. Overall, the prognosis for malignant peritoneal tumors remains poor, with limited treatment efficacy.