Ovarian mixed-epithelial carcinomas with a microcystic pattern and signet-ring cells

Primary ovarian carcinomas with unusual histologic patterns can be difficult to differentiate from metastases. In this study, we reviewed 15 cases of mixed-epithelial carcinoma (12 serous, 1 serous and endometrioid, 1 endometrioid, 1 undifferentiated) with a predominant microcystic pattern and signet-ring cells. The patients' ages ranged from 31 to 78 (mean 58) years. The microcystic component in 11 patients had features of high-grade carcinoma and in 4 patients had features of low-grade carcinoma associated with areas of borderline tumor. The tumors in all 15 patients showed a predominant microcystic growth pattern composed of small cysts that were variable in size and shape. Signet-ring cells were also present in all cases (diffusely in nine cases, focally in six cases) within the neoplastic epithelial proliferation. Mucin was present in the lumina of some of the microcysts and in the cytoplasm of most of the signet-ring cells. A microcystic pattern and mucin-containing signet-ring cells can be seen as small foci or as a predominant component in primary epithelial nonmucinous ovarian carcinomas. It is important for pathologists to recognize these unusual findings in ovarian neoplasms, because they may produce a confusing appearance, even potentially suggesting a metastasis.