The invention features a method for treating patients who have an ALK-driven cancer, which is, or has become, refractory to one or more of crizotinib, CH5424802 and ASP3026, or which bears an ALK mutation identified herein, by administering a compound of formula (I) to the patient. The invention also features methods, kits, and compositions for characterizing ALK-driven cancers to determine whether they express an ALK mutant.