...the patient was diagnosed with cT1N3M1 stage IVB lung adenocarcinoma. An EGFR exon 20 insertion, without any additional mutations, was identified….osimertinib was initiated to treat the EGFR exon 20 insertion-positive lung adenocarcinoma….Although the disease appeared to be stable 2.5 months after the administration of osimertinib, the tumor started to grow 3 months after administration, and carcinoembryonic antigen levels became higher than those before treatment. Thus, osimertinib was discontinued...