ATM (ataxia-telangiectasia mutated) protein kinase, is a member of the serine-threonine kinase family and coordinates cellular responses to DNA damage through activation of distinct DNA repair and signaling pathways. ATM somatic mutations are associated with endometrial, colon, pancreatic, and breast cancers. Simple ATM mutations are seen in about 4% of all cancers, including 9% of colorectal cancers, 8% of skin cancers, and 3% of lung carcinomas. A clinical study has indicated that cancers with ATM mutations may respond to PARP inhibitors.