Compositions and methods for the diagnosis and treatment of a cancer that is resistant to at least one anaplastic lymphoma kinase (ALK) kinase inhibitor are provided herein. The present invention is based on the discovery of mutations within ALK that confer resistance to at least one ALK kinase inhibitor. Polynucleotides and polypeptides having at least one ALK inhibitor resistance mutation are provided and find use in methods and compositions useful in the diagnosis, prognosis, and/or treatment of diseases associated with aberrant ALK activity, more particularly, those that are resistant to at least one ALK kinase inhibitors. Methods and compositions are also provided for the identification of agents that can inhibit the kinase activity and/or reduce the expression level of the ALK resistance mutants.
