PALB2 mutation as a predictive biomarker for immunotherapy in patients with advanced melanoma: Results from (a pooled analysis of) five multicenter, randomized clinical trials.

e21537 Background: PALB2, a gene in the homologous recombination repair (HRR) pathway, has been shown to be associated with the efficacy of platinum based chemotherapy, and PARP inhibitor therapy in breast, prostate, ovarian, and pancreatic cancers. However, their predictive value of PALB2 remained unknown in patients with advanced melanoma. Methods: Five independent cohorts (Miao2018, Samstein2018, Allen 2015, Hugo2016, and Synder2014. study cohort) with data from 672 patients with advanced melanoma were used to analyze the correlation with immunogenic marker, and the prognostic effect of PALB2 on immunotherapy. Results: A pooled analysis of five independent cohorts of 672 advanced patients melanoma show that 31 (4.6%) harbored PALB2 mutation ( PALB2 mut ). PALB2 mut (72.63Muts/Mb) was associated with higher tumor mutation burden (TMB) (P < 0.001) than PALB wild-type ( PALB2 wt ) (19.71Muts/Mb). The same phenomenon has also been observed in TNB, PALB2 mut (1983 counts) was associated with higher tumor neoantigen burden (TNB) than PALB2 wt (603.5 counts) (P = 0.0147). The objective response rate (ORR) of immunotherapy was 53.33% for the patients with PALB2 mut and 24% for the PALB2 wt subgroup (P = 0.027). The PALB2 mut patients had significantly improved median overall survival (mOS) than the PALB2 wt group (Not reach versus 29 months, hazard ratio (HR) = 0.38, 95%CI 0.19−0.73, P = 0.003). A subgroup analysis of CTLA4 inhibitor treatment found that PALB2 mut was associated with better ORR (50% versus 18.3%, P = 0.016) on immunotherapy, and mOS in the PALB2 mut group was significantly better than that in the PALB2 wt group (Not reach versus 21 months, HR = 0.3, 95%CI 0.13−0.68, P = 0.002). However, in the subgroup receiving PD-L1 inhibitor treatment, no ORR benefit was found in the PALB2 mut group (66.67% versus 56.76%, P = 1), and there was no difference on mOS between PALB2 mut and PALB2 wt (Not reach versus 31 months, HR = 0.45, 95%CI 0.11−1.8, P = 0.254). Conclusions: PALB2 mutations was associated with a higher TMB and TNB level. PALB2 may serve as a positive predictor of immunotherapy (CTLA4 inhibitor therapy) in patients with advanced melanoma and their clinical value warrants further investigation.