The relatively poor prognosis of ex20ins patients could be partially explained by the low TMB levels in patients harbouring HER2 ex20ins [29, 41], as advanced NSCLC patients with higher TMB (above 50% percentile) could achieve better PFS than patients with lower TMB (below 50% percentile) [25]. Here, ERBB2 is linked to non-small cell lung carcinoma.