Effects of pharmacokinetics-related genetic polymorphisms on the side effect profile of afatinib in patients with non-small cell lung cancer

•Afatinib plasma concentration correlated to severity of diarrhea as a side effect.•Afatinib plasma concentration was higher in patients with ABCG2 polymorphism.•Diarrhea was more severe in patients with ABCG2 polymorphism.•Genetic polymorphisms of transporters correlated to tolerance of the standard dose.