This approach was chosen for several reasons; 1) the public health impact of lung cancer, 2) lung cancers are frequently treated with inhibitors of EGFR (erlotinib is a first-generation EGFR inhibitor), 3) therapeutic resistance due to EGFR blockade in lung cancer has been well-studied, 4) pre-existing KRAS mutant subpopulations have been shown to drive resistance to EGFR blockage in the treatment of colorectal cancer, and 5) allele-specific competitive blocker-PCR (ACB-PCR) analyses have demonstrated that KRAS mutant subpopulations are prevalent in lung adenocarcinomas. This evidence concerns the gene KRAS and colorectal cancer.