EGFR and non-small cell lung carcinoma: In the APPLE study in EGFR mutant non-small cell lung cancer (NSCLC), ctDNA detection while on gefitinib of the EGFR T790M mutation (which confers resistance to gefitinib) enabled 17% patients to switch therapy to osimertinib (which T790M mutant NSCLC retains sensitivity to) prior to radiological progression.102