Primary ovarian carcinoid arising in associated mature cystic teratoma

Background Primary ovarian carcinoid is a very rare ovarian low-grade neuroendocrine tumor, accounting for about 0.1% of all ovarian neoplasms. Case presentation We reported a case of primary ovarian carcinoid arising from a mature cystic teratoma in a 50-year-old woman. Intraoperative frozen section of left ovarian mass was assessed and a malignant epithelial tumor was considered. Morphologically, the main tumor was composed of cells forming trabeculae, and mature cystic teratoma was observed adjacent to the main part. Immunohistochemistry revealed that the trabecular cells were diffuse positive for pan Cytokeratin, CD56 and synaptophysin with low Ki-67 index (about 1%). Conclusions Careful morphological observation combined with appropriate accessory examination are essential for the diagnosis of primary ovarian carcinoid arising from mature cystic teratoma. In addition, the classification criteria of the primary ovarian neuroendocrine tumor are discussed.