ERBB2 and neoplasm: Thus, it is of great interest to investigate how effective immune monotherapy is in the presence of concurrent high PD-L1 expression and driving gene mutation.<h4>Patients and methods</h4>We present a case of squamous lung cancer with high PD-L1 expression and HER2 exon 20 insertion (20Ins) who presented hyperprogressive disease (HPD) after being treated with PD-1 inhibitor.<h4>Results</h4>A 71-year-old female was diagnosed with advanced squamous lung cancer with 98% tumor proportion score of PD-1 and 20ins.