Abstract
BACKGROUND: Distant metastases from lung cancer are commonly found in the brain, bone, and liver. Metastases to the breast from non-mammary malignancies are extremely rare, and their clinical presentations remain unclear. CASE PRESENTATION: We herein report a case of bilateral breast metastases from anaplastic lymphoma kinase-positive advanced lung cancer in a 51-year-old Japanese male patient. During the course of systemic treatment for advanced lung cancer, computed tomography revealed bilateral breast enlargement without contrast enhancement, a finding consistent with gynecomastia. While other metastatic lesions responded to chemotherapy, both breast masses grew vertically like nodules. The breast masses were immunohistochemically diagnosed as metastases from lung cancer and were removed surgically. Simultaneous bilateral breast metastases from malignancies of other organs, like ones in this case, have rarely been described. CONCLUSIONS: It is important to keep in mind that breast metastases from nonmammary malignancies are a possible explanation for unusual breast findings in a patient with a history of malignancies.