Impact of PD-L1 expression on conventional urothelial bladder carcinoma (UCB) genomic alteration (GA) profile.

Abstract

e16535 Background: Immunohistochemistry (IHC) to determine PD-L1 expression level has been used as a biomarker to predict immune checkpoint inhibitors response in UCB. We hypothesized that the GA profiles would differ between UCB featuring high vs negative PD-L1 expression. Methods: 102 cases of advanced UCB with known PD-L1 tumor cell expression underwent hybrid-capture based comprehensive genomic profiling to evaluate all classes of genomic alteration (GA). Tumor mutational burden (TMB) was determined on up to 1.1 Mbp of sequenced DNA and microsatellite instability (MSI) was determined on 114 loci. Tumor cell (TC) PD-L1 expression was determined by IHC (Dako 22C3). Only PD-L1 high (H) (≥50% TC expression) and negative (N) (0% TC expression) cases were included in this study. Results: Overall, only 2 (8.3%) of the 24 PD-L1H UCB featured CD274 ( PD-L1) amplification (mean 19 copies) and none of 78 PD-L1N had CD274 amplification (P = .05). The gender, age and GA per tumor frequencies were similar in the groups. When compared with the PD-L1H UBC cases, FGFR3 GA were significantly more frequent in the UBC PD-L1N cases (p = .02). Currently “untargetable” GA that were more frequent in the PD-L1H UBC, but did not reach significance, included TP53, TERT and RB1. MTAP loss, a potential target for PRMT5 and MTA2 inhibitors, were 3X more frequent in the PD-L1N UBC. ERBB2 amplification and ERBB3 and PIK3CA short variant (SV) GA were more frequent in the PD-L1N UBC with differences not reaching significance. The mean gLOH scores were similar in both groups. Other ICPI-associated potential biomarkers, including MSI status, TMB level and GA in PBRM1, STK11 and MDM2 were not significantly different in the groups. For UCB cases where a mutational signature could be determined, 15/33 (45%) of PD-L1H and 34/112 (30%, p = 0.14) of PD-L1N UCB featured an APOBEC gene signature; 79% of PD-L1H and 83% of PD-L1N featured European ancestry (p = 0.61). Conclusions: PD-L1H and PD-L1N subtypes of UCB differ in their genomic profiles. PD-L1N UCB features greater frequencies of potentially “targetable” GA, including FGFR3, ERBB2, ERBB3 and PIK3CA. PD-L1 IHC may thus not only play a role in the selection of ICPI for advanced UCB but also in designing trials that may combine ICPI with targeted therapies.[Table: see text]