Second, L858R-positive NSCLC harbours many miscellaneous compound mutations other than EGFR mutation62, whereas Ex19del-positive NSCLC is more likely to be relatively pure with regard to the oncogene mutation that drives proliferation and is mainly dependent on the EGFR pathway, which would result in a long PFS with EGFR-TKIs. The gene discussed is EGFR; the disease is non-small cell lung carcinoma.