Neuroendocrine tumor (NET) of the vagina in the light of WHO 2020 2-tiered grading system: clinicopathological report of the first described case.

Up to now, a vaginal well-differentiated neuroendocrine tumor (NET) has never been well described in the literature. A 2-cm vaginal nodule morphologically revealed a proliferation of mild to moderately atypical eosinophilic epithelioid cells, without tumor cell necrosis. Immunohistochemistry (IHC) showed positivity for CK (AE1/AE3), chromogranin A, and synaptophysin, focal positivity for CDX2, and negativity for PAX8 and TTF1. Metastatic origin was excluded by imaging and the morphological context with benign mucinous glands as present in the surgical resection specimen. Considering mitotic index and Mib1/Ki67 (8 mitoses/2 mm2; >20%), the case was diagnosed as vaginal NET G2 in the light of the WHO 2020 grading system for the gynecologic neuroendocrine neoplasms (NENs). Ranges of Mib1-Ki67 are not yet standardized. Currently, mitotic index and tumor cell necrosis were taken into consideration for the grading system. Gynecologic NENs still represent a diagnostic challenge. A clinico-radiologic workup and an appropriate diagnostic path ruling out the metastatic nature are mandatory to achieve the diagnosis.