Clear cell renal cell carcinoma metastasized by a breast ductal carcinoma

OBJECTIVE: To report a clear cell renal cell carcinoma recipient of a metastasizing ductal carcinoma of the breast: A tumor-to-tumor metastasis. METHODS: A 71 year-old woman with a past history of breast carcinoma, diagnosed 12 years before, underwent nephrectomy for an incidental kidney mass found in a routine imaging examination. RESULTS: Histological examination revealed foci of ductal carcinoma of the breast in an otherwise typical clear cell renal cell carcinoma of the kidney. Immunohistochemical examination confirmed a metastasis of an infiltrating breast carcinoma to a clear cell renal cell carcinoma (positive to GATA3, hormonal receptors and mamoglobin) in a clear cell renal cell carcinoma (positive to PAX8, CD10 and vimentin). CONCLUSIONS: Awareness of this phenomenon should always be kept in mind by urologist in patients with a known history of a previous malignancy and by pathologists when finding a renal tumor with an unusual or dimorphic morphology. Immunohistochemistry plays an important role to establish the exact diagnosis.