Carcinosarcomas (CSs) are rare biphasic neoplasms of the female genital tract, with the presence of malignant epithelial and mesenchymal components. The occurrence of non-epithelial or non-mesenchymal differentiations in CSs is extremely rare. A case of a 54-year-old woman with a history of treatment for breast carcinoma is reported. The patient presented with a uterine tumor showing histological, immunohistochemical, and ultrastructural features of an extremely rare CS, with signs of melanocytic differentiation. The lesion was a 7.0 x 5.6 cm polypoid tumor mass arising from the endometrium and metastasizing in the abdominal cavity as a malignant melanoma - the most aggressive component of CS. Despite adjuvant chemotherapy, she died 8 months after the initial diagnosis due to the metastatic spread of CS. In line with current knowledge, we assess the melanocytic differentiation as one of a hypothetic differential line with the ability of multidirectional stem cell differentiation. We discuss a possible pathogenesis of this lesion and the role of tamoxifen in the tumor development as well. To the best of our knowledge, only one case of uterine CS with melanocytic differentiation has been reported in the English literature.