KRAS mutations are associated with primary resistance to gefitinib or erlotinib in lung adenocarcinomas. A study analyzed 60 lung adenocarcinomas, some sensitive and some resistant to these drugs, and found that KRAS mutations were present in 9 of 38 refractory tumors but none in 21 drug-sensitive tumors. Conversely, EGFR mutations were found in 17 of 22 sensitive tumors but none in 38 resistant ones. These findings suggest that determining the mutational status of both EGFR and KRAS could help identify patients likely to benefit from gefitinib or erlotinib. The study also found that KRAS mutations are rarely found in the same tumors as EGFR mutations, indicating they may have functionally equivalent roles in lung tumorigenesis. The results highlight the importance of testing for both mutations to improve treatment decisions. The study was supported by various grants and institutions, and further research is needed to validate these findings in larger trials.KRAS mutations are associated with primary resistance to gefitinib or erlotinib in lung adenocarcinomas. A study analyzed 60 lung adenocarcinomas, some sensitive and some resistant to these drugs, and found that KRAS mutations were present in 9 of 38 refractory tumors but none in 21 drug-sensitive tumors. Conversely, EGFR mutations were found in 17 of 22 sensitive tumors but none in 38 resistant ones. These findings suggest that determining the mutational status of both EGFR and KRAS could help identify patients likely to benefit from gefitinib or erlotinib. The study also found that KRAS mutations are rarely found in the same tumors as EGFR mutations, indicating they may have functionally equivalent roles in lung tumorigenesis. The results highlight the importance of testing for both mutations to improve treatment decisions. The study was supported by various grants and institutions, and further research is needed to validate these findings in larger trials.