Intramammary Metastasis in a Patient with a History of Renal Cell Carcinoma: A Case Report

: Intramammary metastasis of renal cell carcinoma (RCC) is extremely rare, accounting for only 1.5% of all intramammary metastases. Distinguishing intramammary metastases from benign tumors and breast cancer is clinically problematic. Some patients undergo excessive surgery after a misdiagnosis of breast cancer instead of a mammary tumor. We performed a core needle biopsy (CNB) of a breast mass that developed in a 71-year-old woman after surgeries for bilateral RCC and breast cancer, leading to a diagnosis of intramammary metastasis of RCC. In this case, the CNB and immunohistochemical examination were critical for reaching a definitive diagnosis. We conclude that, when examining patients with mammary tumors, establishing their history of malignant tumors may help diagnose intramammary metastasis and select the best treatment strategy.