Abstract
Renal cell carcinoma (RCC) is the most common and the most lethal urogenital malignancy, and can metastasize rapidly via hematogenous spread. Even so, RCC metastasis within the breast is extremely rare and may appear deceptively benign on screening mammograms. In this article, we present a rare case of RCC that remained undiagnosed until an intra-mammary metastasis was detected on a routine screening mammogram. Further imaging workup and core needle biopsy of the mass ultimately confirmed a new diagnosis of metastatic clear cell RCC. Given that the presence of an RCC breast metastasis indicated advanced-stage RCC, the patient in this case underwent treatment with systemic immunotherapy. This case report describes key imaging features of metastatic RCC on common breast imaging modalities. It underscores the vital role that screening mammography can play in the initial detection of clinically silent, extra-mammary malignancies, including RCC. Thorough imaging workup and tissue biopsy are essential to distinguish a primary breast lesion from intra-mammary metastatic disease, to inform the management plan, and to prevent lumpectomy or mastectomy when it does not benefit the patient.