Metastatic renal cell carcinoma initially presenting as a unilateral breast lump

Breast metastasis from primary renal cell carcinoma is a rare entity and infrequently reported in the literature. We present a case of a 65-year-old lady who presented to breast clinic with a 4-month history of rapidly growing right sided breast lump. She previously had a left mastectomy for breast cancer and a hysterectomy for endometrial cancer. Radiological evaluation with mammography and ultrasound revealed a large heterogeneous right breast lump with prominent vascularity which was biopsied. Histopathological and immunohistochemical features were not supportive of a primary breast carcinoma and favored metastasis from a renal tumor. The patient was unfortunately admitted to hospital due to increasing confusion and neurological symptoms and underwent whole-body cross-sectional CT imaging which demonstrated a giant tumor originating from the right kidney with associated intrathoracic, breast and intracranial metastasis. She was diagnosed with eosinophilic variant metastatic renal cell carcinoma. This case highlights the importance of considering alternative diagnoses to primary breast carcinoma in the context of an initial presentation of a unilateral breast lump.