An unusual case of ovarian high-grade carcinoma and neuroendocrine tumor: Dedifferentiated ovarian carcinoma or mixed adenocarcinoma and neuroendocrine carcinoma? Clinicopathologic features and literature review

Introduction: Undifferentiated and dedifferentiated ovarian carcinomas are rare, aggressive neoplasms. While the dedifferentiated component may exhibit neuroendocrine differentiation, this is typically limited to less than 10% of the tumor. Case Report: We report a unique case of a 73-year-old woman with a high-grade ovarian adenocarcinoma containing a morphologically distinct, diffusely neuroendocrine-rich component. Histologically, the tumor demonstrated two distinct patterns: a well-differentiated yet cytologically high-grade adenocarcinoma adjacent to sheets of monotonous, largely dyscohesive high-grade tumor cells with diffuse neuroendocrine marker expression. The dual morphology raised consideration of a mixed adenocarcinoma–neuroendocrine carcinoma as part of the diagnostic differential. Conclusion: This case describes an uncommon ovarian carcinoma that shows more than 10% diffuse neuroendocrine differentiation which is not typically encountered in dedifferentiated ovarian carcinomas. The combination of high-grade adenocarcinoma with a neuroendocrine-rich component suggests a mixed adenocarcinoma–neuroendocrine carcinoma, a pattern that, to our knowledge, has not been previously documented in the ovary. These observations emphasize the importance of maintaining a broad differential diagnosis when evaluating ovarian carcinomas with prominent neuroendocrine features.