Renal Medullary Carcinoma Masquerading as Bilateral Breast Carcinoma Category: Case Report.

Metastatic disease to the breast accounts for less than 1% of all breast carcinoma. Here we describe an unusual case of a 34-year-old black female with history of sickle cell trait who presented to her gynecologist with bilateral palpable breast masses. Based on initial workup including pathology results from biopsies of both breast masses, she was diagnosed with bilateral breast cancer. However further radiographic imaging revealed a large right kidney mass suspicious for primary renal neoplasm along with lung and bone lesions. This prompted re-review of the initial breast pathology. Sickled erythrocytes were identified and results of an additional immunohistochemical panel revealed positive expression of PAX 8, vimentin, Oct3/4, and loss of INI1, confirming the diagnosis of metastatic renal medullary carcinoma. We discuss the importance of considering renal medullary carcinoma in the differential diagnosis when evaluating young patients with sickle cell hemoglobinopathies who present with aggressive metastatic disease.