Successful Treatment with Crizotinib to Overcome Drug Resistance Possibly Due to Mesenchymal-epithelial Transition Amplification in a Lung Cancer Patient with the Echinoderm Microtubule-associated Protein-like 4-anaplastic Lymphoma Kinase Fusion Gene

Amplification of the mesenchymal-epithelial transition (MET) gene plays an important role in anticancer drug resistance to anaplastic lymphoma kinase-tyrosine kinase inhibitors (ALK-TKIs) in echinoderm microtubule-associated protein-like 4-anaplastic lymphoma kinase (EML4-ALK)-rearranged lung cancer cells. We encountered an ALK-rearranged lung cancer patient who developed MET amplification after alectinib treatment and showed an effective response to fifth-line crizotinib. First-line alectinib treatment was effective for 2.5 years; however, liver metastases exacerbated. Liver biopsy specimens revealed MET and human epidermal growth factor receptor 2 (HER2) amplifications. Switching to the MET inhibitor crizotinib improved liver metastases. Crizotinib may be effective in ALK-positive patients with MET amplification.