A rare case of cancer-to-cancer metastasis: breast cancer to renal cell cancer : Case report and review of literature.

BACKGROUND: Cancer-to-cancer metastasis is very rare with less than 50 cases described in literature. This article reports a case of breast cancer with synchronous metastasis to clear cell renal cell cancer. CASE DESCRIPTION: A 79-year-old woman was diagnosed with a bilateral breast carcinoma. Sonographic staging investigation of the abdomen revealed a 6 cm wide expansion of the right kidney. Bilateral mastectomy and nephrectomy of the right kidney was performed. The histology revealed a clear cell renal cell carcinoma and in the center of the tumor a 0.5 cm metastasis of the breast cancer. The patient's comorbidities and performance status precluded chemotherapy und she received palliative radiotherapy, targeted monoclonal antibody therapy and antihormonal treatment. CONCLUSIONS: Even if cancer-to-cancer metastasis is a very rare phenomenon, the simultaneous or consecutive finding of a renal tumor in women with breast cancer should be carefully evaluated.