Comprehensive genomic profiling of urethral cancer to reveal distinctive features compared to bladder cancer.

Abstract

429 Background: Relapsed and refractory urethral cancer (UrethC) is a rare form of genito-urinary malignancy that includes urothelial carcinoma (UC), squamous cell carcinoma (SCC), adenocarcinoma (AC) and clear cell carcinoma (CCC) subtypes. No standard treatment exists. Methods: DNA was extracted from 40 microns of FFPE specimen from 46 cases of mUrethC. Comprehensive genomic profiling (CGP) was performed using a hybrid-capture, adaptor ligation based next generation sequencing assay to a mean coverage depth of >500X. Tumor mutational burden (TMB) was calculated from a minimum of 1.11 Mb of sequenced DNA as previously described and reported as mutations/Mb. The results were analyzed for all classes of genomic alterations (GA), including base substitutions, insertions and deletions (short variants; SV), fusions, and copy number changes including amplifications (amp) and homozygous deletions. Results: The clinical features, GA, TMB findings in the mUrethC patients and the subtypes of UrethC are shown in the Table. In comparison with 1,183 similarly profiled UC of the bladder (UCB), all 46 mUrethC and the 21 urothelial mUrethC as a separate group widely differed in GA frequencies. With the exception of similar TP53 GA frequencies, there were significantly lower GA in ERBB2, FGFR1-3 and PIK3CAin the mUrethC cases (p<0.0001 for all comparisons) In addition, mUrethC featured as significantly lower frequency of TMB > 20 mut/Mb (4%; p=0.0001). Conclusions: CGP of mUrethC reveals distinctive genomic alteration frequencies among the 4 disease subtypes with higher numbers of GA in the AC than in the UC, SCC and CCC. The TMB appears to be lower in mUrethC than classically seen in UCB where checkpoint inhibition is now approved. Further study of this rare form of genitourinary cancer appears warranted. [Table: see text]