She was diagnosed with stage IV lung adenocarcinoma (LUAD) with EGFR exon 19 deletion (19del) based on imaging and next-generation sequencing (NGS) findings. She received icotinib followed by osimertinib, then acquired EGFR T790M-cis-C797S. She had low tumor mutation burden (TMB) and achieved partial response (PR) to a programmed cell death-1 (PD-1) inhibitor sintilimab combined with platinum-based doublet chemotherapy as late-line treatment lasting more than 5 months.