Penile squamous cell carcinoma (PSCC) with elevated tumor mutational burden (TMB): A genomic landscape study.

Abstract

4 Background: TMB has emerged as a major biomarker of efficacy in immune checkpoint inhibitor (ICPI) therapies in the neoadjuvant, adjuvant and metastatic disease setting in a wide variety of malignancies, but not in PSCC. Methods: 397 clinically advanced (local major recurrence and/or metastatic disease) PSCC underwent hybrid capture-based comprehensive genomic profiling (CGP) to evaluate all classes of genomic alterations (GA). Tumor mutational burden (TMB) was determined on up to 1.1 Mb of sequenced DNA and microsatellite instability (MSI) was determined on up to 114 loci. Trinucleotide mutation signatures were evaluated (Alexandrov, et al. 2013). Genome-wide loss of heterozygosity (gLOH) was determined using validated pipelines and excluding whole-arm and whole-chromosome events. TMB was categorized into three cohorts: <10 mutations/Megabase [muts/Mb] (low), 10-19 muts/Mb (high), and >20 muts/Mb (very high). Tumor cell PD-L1 expression was determined by IHC (Dako 22C3) and defined as tumor proportion score (TPS) >1. The presence of HPV16/18 was determined by next generation sequencing (NGS). Statistical comparisons were corrected for multiple comparisons using the Bonferonni method. Results: There were 339 (85.4%) TMB low, 40 (10.1%) TMB 10-19 and 18 (4.5%) TMB very high PSCC cases in this study. The mean age of PSCC with very high TMB at 70.1 yrs was older than for TMB low at 63.4 yrs (p=.08). There were no significant differences in genomic ancestry among the 3 groups. The TMB 10-19 and TMB very high tended to feature an APOBEC genomic mutational signature more than the TMB low PSCC cases (74 and 76% vs 44%). MSI high status was absent in the TMB low PSCC, but was present in 7.5% of the TMB 10-19 and 11.8% of the TMB very high cases. gLOH levels above 16% were similar in all 3 groups and ranged from 6.2 to 9.4%. GA associated with differences in TMB status in the PSCC cases included higher PIK3CA GA in TMB 10-19 (40.0%) vs TMB low (18.3%; p=.035) and TMB very high (66.7%) vs TMB low (p=.0002). CDKN2A GA were higher in TMB low (45.7%) than in the combined TMB 10-19 + very high (25.9%; p=.049). GA in KMT2D were higher in the combined TMB 10-19 + very high (29.3%) than the TMB low PSCC (7.7%; p=0002). FGFR3 GA were similar in all 3 groups. PD-L1 expression was not significantly different among the 3 groups with TMB low (78.3%), TMB 10-19 (64.2%) and TMB very high (54.5%). HPV identification was more frequent as TMB increased: 28.3% for the TMB low, 50.0% for the TMB high and 58.8% for the TMB very high groups. Conclusions: The evaluation of PSCC by CGP based on TMB levels revels significant differences in biomarkers for the near 15% of cases that have TMB >10 muts/Mb. Further study of TMB as a biomarker in ICPI-based clinical trials for advanced PSCC appear warranted.