Subtypes of EGFR- and HER2-Mutant Metastatic NSCLC Influence Response to Immune Checkpoint Inhibitors

The efficacy of immune checkpoint inhibitors (ICIs) is low among EGFR-mutated non-small-cell lung cancer (NSCLC), although prolonged responses have occasionally been reported. We investigated the association between mutation subtypes and ICI outcomes among HER2- and EGFR-mutated NSCLC.This retrospective single-center study analyzed patients with EGFR- and HER2-mutated advanced NSCLC who received at least 1 cycle of ICI between 2013 and 2019. Patient characteristics, mutation subtype, and ICI outcomes.Among 48 patients with advanced NSCLC, 14 (29%) had HER2 mutations and 34 (71%) had EGFR mutations. EGFR mutations included 16 (47%) exon 19 deletion, 7 (21%) L858R, 5 (15%) uncommon, and 6 (18%) exon 20 insertion. Compared to EGFR-sensitizing mutations (ESMs), HER2 and EGFR exon 20 mutations were associated with a trend toward better response (respectively, ESM, HER2, and EGFR exon 20: 11%, 29%, and 50%; P = .07) and significantly better disease control rates (respectively, 18%, 57%, and 67%; P = .008). Compared to ESM, HER2 mutations (adjusted hazard ratio, 0.35; P = .02) and EGFR exon 20 mutations (adjusted hazard ratio, 0.37; P = .10 trend) were also associated with improved PFS. Programmed death ligand 1 (PD-L1) expression remained an independent predictor of PFS (adjusted hazard ratio, 0.42; 95% confidence interval, 0.23-0.76; P = .004). The 6-month PFS rates were 29% (HER2), 33% (EGFR exon 20), and 4% (ESM). ICIs were generally well tolerated in this population. Importantly, no immune-related toxicity was observed in 10 patients who received a tyrosine kinase inhibitor (TKI) as the immediate next line treatment after ICI.HER2 and EGFR exon 20 mutations derive greater benefit from ICIs with comparable PFS to wild-type historical second/third-line unselected cohorts. ICIs remain a treatment option for this genomic subgroup, given the absence of approved targeted therapies for these rare mutations.