Beyond CPS for PD-L1 scoring: Genetic alterations that impact efficacy of immunotherapy in hepatocellular carcinoma (HCC).

Abstract

592 Background: Tumor-agnostic approvals of immune checkpoint inhibitors (ICI) include deficient mismatch repair/microsatellite instability high (dMMR/MSI-H) and high tumor mutational burden (TMB) while in cancer like metastatic gastroesophageal cancers, ICI use has been predicated on PD-L1 expression. ICI are increasingly used for metastatic HCC, but without required markers. We aimed to examine the genomic landscape of HCC in context of PD-L1 expression, and to determine clinical responses to ICI in this setting. Methods: Next-generation sequencing of DNA (592 or WES) and RNA (WTS) was tested at Caris Life Sciences (Phoenix, AZ). PD-L1 expression was tested by IHC (SP142) and compared as high (2+,5%), low (1-2,1%) and negative (0). dMMR/MSI-H was tested by IHC/NGS and TMB-High was defined as ³10 mutations/MB. QuantiSEQ was used to estimate the tumor microenvironment. X2/Fisher-Exact were used and significance was determined as P-value adjusted for multiple comparison ( Q < 0.05). Real-world overall survival (rwOS) was obtained from insurance claims and calculated from tissue collection to last contact; time-on-treatment (TOT) was calculated from start to finish of ICI treatments. Results: Overall, 17.7% of HCC expressed PD-L1 by IHC; 79/1306 (6.1%) had high expression. The overall prevalence of dMMR/MSI-H was 0.2%; TMB was high in 5.1%. PD-L1 expression was not associated with MSI-H or high TMB. When comparing tumors that are PD-L1 high vs. negative vs. low, expression of several immuno-oncologic (IO) markers LAG3 (median TPM: 2.4, 0.8, 0.5), CTLA-4 (2.9, 1.2, 0.5), IDO1 (4.2, 1.3, 0.6) and others, as well as T-cell inflamed and IFNg scores all decreased significantly with PD-L1 (all q<0.05), similar trends were seen with B cells, M1 macrophages, CD8+ T cells and T regs while opposite differences seen in NK cells (q<0.05). Additionally, when PDL1-high tumors were compared to PDL1-negative, mutations in CTNNB1 trended lower (21% vs 35%) while amplifications of KRAS (4% vs 0%), PDCD1LG2 (4% vs 0%) and mutations in HNF1A (3% vs 0%), HOXB13 (6% vs 0%), STK11 (5% vs 0%) trended higher; when PDL1-low were compared to PDL1-negative, mutations in TP53 (45% vs 32%), ELF3 (3% vs 0%), TSC2 (6% vs 2%) and PIK3CA (5% vs 1%) and amplifications in BCL9 (2% vs 0%) and CCNE1 (2% vs 0%) trended higher. When investigating clinical outcome of a cohort of 908 HCC tumors, PD-L1 expression had no effect on prognosis, and was not associated with differences in TOT of ICI in HCC. Conclusions: Prevalence of dMMR/MSI-H and TMB-H is very low in HCC. PD-L1 is only expressed in <20%. Even with a finding of strong association of expression of several established IO biomarkers with PD-L1 expression, it’s still not predictive of response to ICI. New biomarkers or molecular signatures need to be identified and validated to objectively identify HCC patients most likely to benefit from ICI treatment.