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Primary Peritoneal Carcinoma — SCE Medical Oncology MCQ

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ModerateCancer of Unknown PrimaryPrimary Peritoneal CarcinomaSCE Medical Oncology

A 50-year-old woman presents with multiple peritoneal deposits and ascites. Biopsy shows high-grade serous adenocarcinoma. Immunohistochemistry: PAX8+, WT1+, CK7+, ER weakly positive, p53 aberrant (overexpressed). CA-125 is 850 U/mL. CT shows no clear ovarian mass. What is the most likely diagnosis?

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Correct answer: D — Primary peritoneal carcinoma

The immunophenotype (PAX8+, WT1+, CK7+, p53 aberrant) is characteristic of high-grade serous Müllerian carcinoma. In the absence of an identifiable ovarian mass, primary peritoneal carcinoma is the most likely diagnosis. This is managed identically to advanced ovarian cancer with platinum-taxane chemotherapy and potential PARP inhibitor maintenance. Primary peritoneal cancer, fallopian tube cancer and ovarian cancer are now grouped together as high-grade serous tubo-ovarian/peritoneal cancer.

Reference: ESMO 2024 Ovarian Cancer Guidelines; NICE NG Ovarian cancer pathway