Genome-wide CRISPR knockout (CRISPRn) and activation (CRISPRa) screens were performed in the EGFR mutant lung cancer cell lines PC-9 and HCC827 as well as isogenic clones (PC-9T790M and HCC827T790M) harbouring the secondary EGFR T790M resistance mutation (which is responsible for resistance in the majority of patients treated with gefitinib in the 1st line setting). The gene discussed is EGFR; the disease is lung cancer.