Small Cell Lung Cancer with Metastasis to the Breast: A Case Report and Review of the Literature

Metastasis to the breast represents 0.4-1.3% of all breast malignancies. In those rare instances, the primary site is usually leukemia, lymphoma, or melanoma. Lung cancer, mostly adenocarcinoma, has been reported to be associated with metastasis to the breast. We report a rare case of a female patient with a rapidly growing breast metastasis from a small cell lung cancer, as a first site of recurrence, misread as a triple negative breast cancer. A full immunohistochemical panel, including ER, PR, Her2/Neu, TTF-1, CK7/CK20, and chromogranin should be employed to confirm the pathology. Differentiating between a newly diagnosed primary breast cancer and metastatic small cell cancer to the breast is important because recurrent small cell lung cancer has a worse prognosis and is treated differently.