Morphologic, immunohistochemical, and preliminary molecular findings of primary ovarian carcinoid tumors in a tertiary center cohort.

Primary ovarian carcinoid tumors (POCTs) are rare, well-differentiated neuroendocrine neoplasms that most frequently originate within mature cystic teratomas or struma ovarii. Currently, there is no formally established malignancy grading system for POCTs, and their genomic characteristics remain relatively understudied. In this study, we aim to extend the understanding of teratoma-associated ovarian tumors and provide a foundation for refining their classification and management. We retrospectively analyzed the clinicopathological, immunohistochemical, and molecular features of 13 POCTs. The cohort consisted predominantly of postmenopausal women (median age 55 years), with strumal carcinoid (53.8%) the most common subtype. All tumors were confined to the ovary and arose in association with a teratomatous background. Notably, nearly half of the patients (46.2%) demonstrated clinical or pathological evidence of estrogen excess, including two cases with concurrent endometrial carcinoma. Immunohistochemically, all tumors were diffusely positive for synaptophysin, while CDX2 and TTF-1 showed limited utility for subtype classification or determination of primary origin. Ki-67 indices were uniformly low (<5%). Next-generation sequencing of five tumors revealed a heterogeneous mutation profile. A likely pathogenic ARID1A p.Q1494* variant was identified in one mixed-architecture POCT with insular and trabecular components, lymphovascular invasion, and a relatively higher Ki-67 index in the insular component; however, this isolated finding should be interpreted as exploratory and requires validation in larger cohorts. To our knowledge, this likely pathogenic ARID1A variant is sporadically identified in one POCT case for the first time in published literature, warranting further investigation.