We report a rare case of a 69-year-old woman who developed three different primary cancers, including non-small cell lung cancer (NSCLC) in both lungs and pancreatic adenocarcinoma, and was later found to have a rarely reported variant mutation in the ATM gene, namely Exon 39, c.5644 C > T. We hypothesize that the ATM gene, c.5644 C > T mutation could be a plausible contributor in the pathogenesis of these three cancers. This evidence concerns the gene ATM and non-small cell lung carcinoma.