Remote Development of Tumor-to-Tumor Metastasis of Breast Adenocarcinoma in a Renal Oncocytoma

Tumor-to-tumor metastasis (TTM) is a rare phenomenon where a focus of distinct metastatic disease is discovered with a second primary tumor. Although renal cell carcinoma is the most frequent recipient of metastatic tumor cells, oncocytomas have also previously been described. We present the case of a patient with incidentally detected mammary adenocarcinoma within an oncocytoma 16 years following primary treatment. The mass was treated with partial nephrectomy, with the surgical pathology specimen showing clear delineation of the pleomorphic lobular carcinoma and oncocytoma cells.