Tumor-to-tumor metastasis: case report of a pulmonary adenocarcinoma metastatic to a clear cell renal cell carcinoma.

Tumor-to-tumor metastasis is a very rare event. The recipient tumor may be benign or malignant. Renal cell carcinoma is the most common tumor recipient of metastasis while lung carcinoma is the most common donor tumor. We report a 57-year-old Caucasian male who presented with chest pain. On PET CT Scan, he was also found to have a large renal mass for which he underwent left nephrectomy. On histology of the renal mass, the tumor was a conventional renal cell carcinoma with areas of metastatic non-small cell lung carcinoma. The two components had a distinctive morphology which was confirmed on subsequent immunohistochemistry. The physiopathological mechanisms making clear cell renal cell carcinoma an avid recipient of a metastatic carcinoma have been speculated upon, but are still unknown.