Osimertinib, a third-generation EGFR tyrosine kinase inhibitor has demonstrated efficacy in tumors harboring the EGFR T790M resistance mutation. Inevitably, resistance to third-generation inhibitors results in disease progression, with the EGFR C797S mutation being one of several resistance pathways identified to date. On the basis of preclinical data, we report what is the first known case of a patient harboring the T790M and C797S mutations in trans treated with combination gefitinib and osimertinib.
