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

Primary ovarian carcinomas with unusual histologic patterns can be difficul t to differentiate from metastases. In this study, we reviewed 15 cases of mixed-epithelial carcinoma (12 serous, 1 serous and endometrioid, 1 endomet rioid, I undifferentiated) with a predominant microcystic pattern and signe t-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 a nd in 4 patients had features of low-grade carcinoma associated with areas of borderline tumor. The tumors in all 15 patients showed a predominant mic rocystic growth pattern composed of small cysts that were variable in size and shape. Signet-ring cells were also present in all cases (diffusely in n ine cases, focally in six cases) within the neoplastic epithelial prolifera tion. 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 impo rtant for pathologists to recognize these unusual findings in ovarian neopl asms, because they may produce a confusing appearance, even potentially sug gesting a metastasis.