Bilateral breast adenocarcinomas with EML4–ALK fusion in a patient with multiple metastases successfully treated with crizotinib: is lung the primary site?

Breast metastases from non-mammary cancers are rare, especially when they appear synchronously. Clinically, it is vitally important to accurately diagnose these patients, as this will directly influence their treatment and survival. We present a very rare and complex case of bilateral breast adenocarcinomas with an EML4–ALK fusion, which was diagnosed as bilateral breast metastases of non-small-cell lung cancer by immunohistochemistry and comprehensive genomic investigation. The patient was successfully treated with an ALK inhibitor (crizotinib); symptoms improved quickly after initiation of crizotinib therapy, and a partial response was observed after 3 months. The experience of diagnosis and treatment of this case indicates the importance and necessity of genomic investigations in such patients, and suggests that we need to consider the rare possibility of this kind of metastasis in order to provide optimal treatment.