Endometrial carcinoma with diffuse melanocytic differentiation: Clinicopathological and molecular analysis of a case with literature review and focus on differential diagnosis.

Herein, we present a clinicopathological and molecular analysis of a case of endometrial carcinoma with diffuse melanocytic differentiation with literature review. A 72-year-old woman underwent hysterectomy due to a 14 cm endometrial mass. On histology, the tumor showed a serous carcinoma component and a solid component with giant eosinophilic and dyshesive multinucleated cells. Differential diagnosis included several entities, such as undifferentiated giant cell carcinoma and carcinosarcoma with rhabdomyoblasts. The solid component showed diffuse positivity for cytokeratin AE1/AE3, Melan A, Cathepsin K and S100, focal HMB45 positivity and loss of e-cadherin. The tumor was p53-abnormal, mismatch repair-proficient and POLE-wild-type. The patient had extrauterine metastases and was alive with disease at 12 months. Previous cases of endometrial and ovarian carcinomas with melanocytic differentiation (n = 7) did not show giant bizarre cells but showed melanin production; all cases were advanced and/or had unfavorable outcomes. In conclusion, endometrial carcinomas with melanocytic differentiation are highly aggressive tumors which should be distinguished from other entities. Being aware of this entity may help not to miss it.