Fine-needle aspiration of metastatic renal-cell carcinoma masquerading as primary breast carcinoma

This report details a fine-needle aspiration biopsy performed in the investigation of two right breast nodules in a patient with previous history of lumpectomy for infiltrating ductal carcinoma in the same breast 3 years before. Because the cytology was atypical for a mammary carcinoma and cells did not match the morphology of the previous breast carcinoma, a tissue biopsy was recommended, revealing the presence of metastasis from a previously silent primary renal-cell carcinoma. This report illustrates not only how metastatic lesions in the breast can masquerade clinically as a primary carcinoma but also the necessity for the cautious approach to interpreting the fine-needle aspiration biopsy of these lesions. Furthermore, essential guidelines necessary to distinguish primary from metastatic lesions in the breast are presented.