Malignant melanoma with metastasis to adenocarcinoma of the prostate.

Tumor-to-tumor metastases are uncommon despite the fact that the presence of two or more malignancies in a single patient is not a rare occurrence. The most frequent donor tumors are the lung, prostate, and thyroid gland, whereas renal cell carcinoma is by far the most common recipient. In this report we describe a patient dying of metastatic malignant melanoma and locally advanced prostate cancer in which the melanoma metastasized to the prostatic adenocarcinoma. The prostatic primary was well differentiated and stained positively with prostate-specific antigen and prostatic acid phosphatase, whereas the melanoma contained abundant melanin pigment and stained positively for S-100 protein. This is the second reported instance of prostatic carcinoma as the recipient in a case of tumor-to-tumor metastases and the first in the English language literature.