Metastatic Nodular Melanoma with Angiosarcomatous Transdifferentiation-A Case Report and Review of the Literature.

Diagnosing cutaneous melanomas relies mainly on histopathological analysis, which, in selected cases, can be aided by immunohistochemical evaluation of conventional melanocytic markers. Nevertheless, these malignancies, particularly in metastatic settings, may display divergent differentiation with unusual histological and immunohistochemical features. In this context, we present the case of a 65-year-old male diagnosed with typical superficial spreading melanoma who developed recurrence and metastatic lesions featuring angiosarcomatous differentiation. The diagnosis of the initial tumour and the subsequently dedifferentiated lesions was confirmed by ample immunohistochemical analysis, which included several melanocytic markers, as well as mesenchymal and vascular markers. The recurrent tumour and lymph nodes metastases were completely negative for Melan-A and PRAME, and focally positive for SOX10. Additionally, they also displayed diffuse, intense positivity for CD10 and WT1 and focal positivity for CD99, ERB, and CD31. Thus, the diagnosis of primary cutaneous melanoma with recurrent and metastatic divergent angiosarcomatous differentiation was established. This occurrence is particularly rare and can pose important diagnostic challenges. Therefore, in addition to presenting this highly unusual case, we also performed a comprehensive review of the literature on divergent differentiation in melanomas.