Genomic and Immunologic Profiles of Concurrent RB1 and CDKN1A/p21(WAF1) Truncating Mutations (RW+) in Bladder Cancer.

4571 Background: p53 target and cell cycle inhibitor CDKN1A/p21(WAF1) was initially not found to be mutated in cancer. TCGA analysis identified CDKN1A mutations are present but rare with frequencies of < 1%, but enrich in bladder cancer (̃8%). Truncating WAF1 mutations are associated with sensitivity to cisplatin and are associated with truncating Rb mutations in bladder cancer (RW+). We hypothesized RW+ bladder cancers may represent a unique subgroup with sensitivity to therapeutics. Methods: A total of 1104 urothelial tumors underwent molecular profiling at Caris Life Sciences (Phoenix, AZ) utilizing NGS of DNA (592 Gene Panel, NextSeq, or WES, NovaSeq) and RNA (NovaSeq, WTS). Wilcoxon, Fisher’s exact were used for statistical significance (p value without and q value with multi comparison correction). Immune cell fraction (QuanTIseq) and pathway analysis (ssGSEA) were assessed by mRNA analysis. Immune epitope prediction was performed using the NetMHCpan v4.0 method in the Immune Epitope Database. Results: Concurrent truncating mutation (frameshift, nonsense) for RB1 and WAF1 were detected in 47 tumors (RW+, 4.25%) and tumors with wild-type status for both RB1 and WAF1 genes were classified as RW- group (54.08%). Tumors harboring only one RB1 or WAF1 mutation were excluded for further analysis. When compared to RW- group, RW+ tumors showed lower mutation rate of TP53 (54.5% vs 80.9%, q < 0.05), ARID1A (23.5% vs 38.3%, p < 0.05), and PIK3CA (18.4% vs 31.9%, p < 0.05). Interestingly, RW+ was mutually exclusive with FGFR3 mutation (18.0% vs 0%, p < 0.05). We further evaluated RNA expression of DNA repair and checkpoint arrest pathways. Notably, E2F pathway (Normalized Enrichment Scores, NES: 0.89 vs 0.86, q < 0.01) and DNA G2M checkpoint (NES: 0.89 vs 0.86, q < 0.01) were found to be the most enriched in RW+ with respect to RW- group. In addition, mRNA levels of FANCC/A, CHEK1, WEE1, CDC25A/C, PALB2 and BRCA1/2 were found to be overexpressed in RW+ group (q < 0.05). RW+ tumors also displayed a distinct immunological profile: They were associated with higher PD-L1 status (63.8% vs 37.3%, q < 0.01), higher median TMB (11 mut/Mb vs 8 mut/Mb, q < 0.01) and with less frequent loss of heterozygosity for HLA-DPA1 (51.1% vs 66.7%, p < 0.05), with more high-binding-affinity neoantigen load (4.78 vs 3.89, p < 0.05) to MHC proteins, consistent with the significantly more myeloid dendritic cells in in RW+ group (0.3 vs 0.04, q < 0.001). Conclusions: Concurrent truncating mutation in RB1 and WAF1 (RW+) bladder carcinomas have fewer p53, ARID1A, and PIK3CA mutations but are enriched for E2F targets, G2/M checkpoint genes, FANCC/A, CHEK1, WEE1, CDC25A/C, PALB2 and BRCA1/2 and have a distinct immunological profile. The findings suggest therapeutic strategies for RW+ bladder cancers including Chk1/Wee1, PARP inhibitors, -/+ immunotherapy that may impact on clinical outcomes.