[Cancer-to-cancer metastasis: amelanotic melanoma into renal cell carcinoma]

A 54-year old man was admitted because of motor aphasia, behavioral changes and weight loss and suffered from a widely disseminated cancer with unknown primary origin (CUP) syndrome.

The autopsy revealed that he was affected by two malignant neoplasms simultaneously: an amelanotic malignant melanoma metastasizing into a localized renal cell carcinoma.

Cancer-to-cancer metastasis is an exceedingly rare, but well documented phenomenon. This is the third reported case of a malignant melanoma as donor tumor spreading into a renal cell carcinoma. Well-vascularized and slowly growing renal tumors are typical recipients for cancer-to-cancer metastases. The amelanotic character of the melanoma exerted a special diagnostic challenge. Clinical and autopsy findings as well as the immunophenotypical features of the metastatic amelanotic melanoma (HMB-45, Melan-A/MART-1, S100) and the renal cell carcinoma are described with a review of the relevant literature.