Background: The EML4-ALK fusion oncogene is found in 2 to 7% of all non-small cell lung cancers, most of which are adenocarcinomas. These rare ALK-positive lung malignancies represent approximately 4% of all adenocarcinoma non-small-cell lung cancer; metastatic spread to the breast is exceedingly rare, with an incidence between 0.2-3% of reported cases. Here we present a case of ALK-positive lung cancer metastasizing first to the breast and then to the spine.

Case Report: A 60-year-old female with a left upper lobe pulmonary lesion suspicious for malignancy underwent a wedge resection; pathology revealed pulmonary adenocarcinoma with positive nodes. While an EML4-ALK fusion was identified, the patient refused adjuvant therapy. One month later, a 7mm lesion in the right lower mid-breast was identified; a biopsy identified poorly differentiated carcinoma consistent with lung origin. Pemetrexed, Cisplatin, and Carboplatin were initiated. Two months later, with new onset of back pain, a PET scan revealed a hypermetabolic bony lesion in the third lumbar vertebral body. A biopsy revealed metastatic adenocarcinoma from the lung. The patient began radiation therapy and, given the EML4- ALK fusion, transitioned from standard chemotherapy to targeted therapy. Currently, following the completion of radiation therapy, the bony metastasis has resolved, and the patient continues to tolerate targeted therapy well.

Conclusion: Metastases to the breast from other primary locations account for only 0.2-1.3% of all breast malignancies, but most often, these are lung cancer. EML4-ALK fusions are found in 2-7% of pulmonary adenocarcinomas, but indicate the use of targeted therapy which portends a high and durable response rate. This is the fifth EML4-ALK fusion oncogene identified in lung cancer metastasis to the breast that is managed with targeted therapy, emphasizing the importance of bioanalysis in management.