The echinoderm microtubule-associated protein-like 4 (EML4)–anaplastic lymphoma kinase (ALK) is a recently identified fusion-type oncoprotein that exists in approximately 5% of non-small cell lung cancer (NSCLC). It has been demonstrated that NSCLC driven by EML4-ALK is strongly addicted to this fusion-type oncokinase. A clinical trial of crizotinib (PF-02341066) sponsored by Pfizer has proven this oncogene addiction in humans by demonstrating a high response rate to inhibition of ALK kinase activity. In the present study, we report on three cases harboring EML4-ALK rearrangement who were enrolled in the trial (A8081001, NCT00585195). All three patients showed favorable responses to the ALK-specific tyrosine kinase inhibitor. (Cancer Sci 2011; 102: 1602–1604)