Answer: Micropapillary serous carcinoma

Histology: The tumor is composed of delicate papillae, which are five times longer than they are wide (micropapillary pattern). There are areas showing features of early tissue invasion with epithelial tufts surrounded by clear spaces or clefts. The neoplastic cells show mild to moderate nuclear atypia and rare mitotic figures. Psammoma bodies are abundant.

Discussion: The term micropapillary serous carcinoma (MPSC) was recently introduced to define a subset of serous ovarian tumors, which have a unique histologic pattern and are prognostically different from serous borderline tumors and invasive serous carcinomas of the ovary (Am J Surg Pathol. 1996 Nov;20(11):1319-30). Recent studies have revealed that MPSCs behave in an indolent fashion and can recur after many years. In addition MPSCs do not appear to respond to current regimens of chemotherapy. Tissue invasion can often be difficult to determine in cases of borderline or micropapillary serous tumors involving extraovarian sites (peritoneal “implants”). A recent publication, however, has shown that the histologic feature of epithelial tufts surrounded by clear spaces or clefts, does help predict a poor clinical outcome (Am J Surg Pathol, 25(4):419-32,2001). Florid mesothelial hyperplasia can be difficult to distinguish from metastatic and primary peritoneal serous carcinomas. Grossly visible ovarian or peritoneal tumor and large numbers of psammoma bodies all favor the diagnosis of a serous tumor. Immunohistochemical markers showing epithelial differentiation (BerEP4) or mesothelial derivation (calretinin, mesothelin) may also be of value in the differential diagnosis.