Primary Small Cell Neuroendocrine Carcinoma of the Endometrium: A Cytologically Diagnosed Case with Immunocytochemical, Immunohistochemical, and Electron Microscopic Features

Endometrial neuroendocrine tumors are rare, accounting less than 1% of endometrial cancers. They include small cell neuroendocrine carcinoma (NEC) and large cell NEC and usually occur in postmenopausal patients. Although common symptoms include postmenopausal bleeding, most patients are diagnosed at an advanced stage. We report an extremely rare case of small cell NEC developed in the endometrium of a 75-year-old Japanese woman. This case was initially suspected based on the findings of endometrial cytology: a number of small round malignant cells were present on the endometrial smear specimens. The immunocytochemical and immunohistochemical examinations revealed diffusely cytoplasmic positive reaction of neuron specific enolase (NSE) and partially membranous positive reaction of CD56 in the small cancer cells. They showed PAX-8-positive reaction, but did not express microsatellite instability high. Electron micrography showed several dense-core secretory granules in the cytoplasm of cancer cells. Despite multiple lung metastases, the patient underwent a hysterectomy and salpingo-oophorectomy in order to control excessive genital bleeding. She received six courses of adjuvant chemotherapy based on etoposide and cisplatin, and survived healthy eight months after the first visit without any viability of lung metastases.