Discrepancies in response and immune-related adverse events (irAE) of anti-PD-1 monotherapy between races and primary sites in patients (pts) with advanced nonacral cutaneous melanoma (NACM).

Abstract

9530 Background: Ultraviolet (UV)-induced high tumor mutation burden (TMB) of NACM is associated with response to anti-PD-1 monotherapy (aPD-1). Anatomic location of the primary lesion (reflecting UV exposure) and race (reflecting eumelanin level) may serve as surrogates for TMB and be associated with varying response and irAE patterns. Methods: Pts with advanced NACM receiving aPD-1 between 2009-2019 were retrospectively analyzed from 5 institutions in the US, Australia and China. Best response, survival (PFS and OS), and organ/system-specific irAEs were compared by race (Caucasian [C] vs non-Caucasian [NC]) and primary anatomic site. Results: Among 697 patients, 616 were C, 81 were NC. Complete response rate (CRR) was 24.8% (95%CI, 21.4-28.4) and 2.6% (95%CI, 0.3-9.1) and ORR was 54.9% (95%CI, 50.9-58.9) and 15.6% (95%CI, 8.3-25.6) in C and NC, respectively (both P<.001). Median PFS was 16.5 (95%CI, 12.0-23.1) and 5.2 (95%CI, 3.6-7.6) months, median OS was 60.5 (95%CI, 49.9-not reached [NR]) and 29.2 (95%CI, 17.9-NR) months, in C and NC, respectively (P<.001 and =.04). In multivariate analyses, C had significantly higher CRR (OR 13.4, 95%CI 3.1-57.4), ORR (OR 10.6, 95%CI 4.6-24.5), and longer PFS (HR 0.5, 95%CI 0.4-0.7) than NC. Compared to a head primary site, NACM from less UV-exposed regions had significantly lower CRR (upper trunk, OR 0.6, 95%CI 0.4-0.96; lower limb, OR 0.5, 95%CI 0.2-0.9), ORR (lower limb, OR 0.6, 95%CI 0.3-0.9) and poorer PFS (perineum/buttock, HR 2.1, 95%CI 1.2-3.5; lower limb, HR 1.6, 95%CI 1.2-2.2) and OS (perineum/buttock, HR 3.8, 95%CI 2.2-6.8; lower limb, HR 1.7, 95%CI 1.2-2.4). Overall irAE incidence was similar between C and NC but irAE subtypes varied. C had significantly higher incidence of GI (12.2%, 95%CI 9.5-15.3% vs 1.2%, 95%CI, 0.03-6.7%, P=.001), respiratory (10.3%, 95%CI 7.8-13.2% vs 0, P<.001) and grade 3/4 (15.4%, 95%CI 12.4-18.8% vs 6.2%, 95%CI 2.0-13.8%, P=.03) irAEs; and lower incidence of endocrine (13.8%, 95%CI 10.9-17.0% vs 32.1%, 95%CI 22.2-43.4%, P<.001) and liver (4.8%, 95%CI 3.2-7.1% vs 13.6%, 95%CI, 7.0-23.0%, P=.005) irAEs. IrAEs did not vary by primary NACM site. Conclusions: Race and primary site are independently correlated with distinct response and survival outcomes in pts with advanced NACM receiving aPD-1. IrAE subtypes vary by race although overall irAE incidence does not.