['Some studies have shown that epidermal growth factor receptor (EGFR) mutations can be heterogeneously distributed in individual tumors. In this study, we re-evaluated the distribution of EGFR mutations within tumors.', 'We used multiple approaches, including an analysis of simultaneous dual hot spot mutations, a trans-sectional analysis of individual lung adenocarcinomas, and comparisons of the mutation patterns between primary and metastatic sites and between primary and recurrent tumors.', 'None of the 862 tumors harboring an EGFR mutation showed simultaneous dual hot spot mutations, although identical EGFR mutations were found throughout individual tumors in a trans-sectional analysis involving 50 tumors divided into three parts and five lung adenocarcinomas divided into 100 parts. In addition, no discordant mutation patterns were detected among 77 paired primary and metastatic site samples or among 54 primary and recurrent tumor pairs.'] Is heterogeneous distribution of EGFR mutations extremely rare in lung adenocarcinoma?