MLH1 V384D polymorphism was reported to be associated with primary resistance to EGFR-TKI in lung adenocarcinoma patients with exon 21 L858R mutation.[27] However, further study to elucidate the differences in mechanisms related to sensitivity to EGFR-TKI between L858R and exon 19 deletion mutations is still warranted. The gene discussed is EGFR; the disease is lung adenocarcinoma.