This study investigates the relationship between KRAS mutations and the primary resistance of lung adenocarcinomas to the kinase inhibitors gefitinib and erlotinib. The researchers screened 60 lung adenocarcinomas, 38 of which were refractory to either drug, for mutations in the *EGFR* and *KRAS* genes. They found that 24% of refractory tumors had KRAS mutations, while none of the drug-sensitive tumors had such mutations. Conversely, 77% of drug-sensitive tumors had *EGFR* mutations, compared to zero in the refractory tumors. The results suggest that KRAS mutations are associated with a lack of sensitivity to these drugs, and that determining the mutational status of both *EGFR* and *KRAS* may help predict which patients are likely to benefit from gefitinib or erlotinib treatment. The findings have important clinical implications, as they could improve treatment decisions and reduce the use of these expensive and potentially harmful drugs in patients who are unlikely to respond. However, larger prospective trials are needed to validate these findings.This study investigates the relationship between KRAS mutations and the primary resistance of lung adenocarcinomas to the kinase inhibitors gefitinib and erlotinib. The researchers screened 60 lung adenocarcinomas, 38 of which were refractory to either drug, for mutations in the *EGFR* and *KRAS* genes. They found that 24% of refractory tumors had KRAS mutations, while none of the drug-sensitive tumors had such mutations. Conversely, 77% of drug-sensitive tumors had *EGFR* mutations, compared to zero in the refractory tumors. The results suggest that KRAS mutations are associated with a lack of sensitivity to these drugs, and that determining the mutational status of both *EGFR* and *KRAS* may help predict which patients are likely to benefit from gefitinib or erlotinib treatment. The findings have important clinical implications, as they could improve treatment decisions and reduce the use of these expensive and potentially harmful drugs in patients who are unlikely to respond. However, larger prospective trials are needed to validate these findings.