EGFR and non-small cell lung carcinoma: These seemingly higher efficacies of afatinib in brain metastasis cohort may be partly explained by the previous studies which analyzed first- and second-generation EGFR-TKI concentrations in human cerebralspinal fluid35,36 where afatinib treatment was likely associated with a larger margin of differential between the measured drug concentration in cerebralspinal fluid and the reported data of in vitro IC50 against NSCLC cell lines with EGFR-sensitizing mutation37.