Ascitic fluid cytology of a malignant mixed Müllerian tumor of the peritoneum: a report of two cases with special reference to p53 status.

Malignant mixed müllerian tumors (MMMTs) rarely originate in the female peritoneum. Peritoneal MMMT, as well as its uterine or ovarian counterpart, is characterized by biphasic histologic components, including carcinoma of the müllerian type and sarcoma. In ascitic fluid cytology of MMMT, however, the biphasic pattern is less evident than in tissue sections, and heterogeneity of cell differentiation makes the cytologic diagnosis difficult, especially in distinguishing tumor cells from reactive mesothelial cells. Here, we report ascitic fluid cytology for two peritoneal MMMT cases. Immunocytochemistry for p53 was helpful in identifying malignant cells; tumor cells in ascitic fluid smears, as well as carcinomatous cells and sarcomatous cells in tissue sections, showed distinct nuclear immunostaining for p53, whereas mesothelial cells did not. Subsequent molecular genetic analysis confirmed frameshift mutations in both cases. To the best of our knowledge, this is the first report showing p53 overexpression and its genetic background in MMMT of the peritoneum.