Merkel cell carcinoma presenting as malignant ascites: A case report and review of literature

The most common site of metastasis to ascitic fluid in females is from a mullerian (ovarian) primary, whereas in males it is from the gastrointestinal tract. Metastatic Merkel cell carcinoma (MCC) to the ascitic fluid is extremely rare and may present as a diagnostic challenge on effusion cytology. In a review of the literature, there are only two case reports of metastatic MCC in pleural effusion. To the best of our knowledge, we present the first cytological diagnosis of MCC metastatic to the ascitic fluid. We describe the cytologic findings as well as the immunohistochemical stains supportive of the diagnosis. Given the fatal prognosis of this tumor compared to melanoma and rarity of its occurrence in ascitic fluid, awareness of this tumor and use of immunohistochemical stains are critical in arriving at the diagnosis.