Clinical and Molecular Characterization of Clear Cell Adenocarcinoma of the Urinary Tract: A Multi-Institutional Study.

Clear cell adenocarcinoma of the urinary tract (CCA-UT) is a rare, potentially aggressive tumor with very limited information regarding its clinicopathologic characteristics and molecular alterations. This study aimed to elucidate the clinicopathologic features and molecular landscape of one of the largest cohorts (35 cases) of this tumor, to identify genomic alterations and potential therapeutic targets. Seventy-nine percent of the patients were women, with a median age of 61 years. The urethra was the most common site (18; 51%), and all cases were ≥pT2 (pT2:15; pT3:11; pT4:8). Twenty-nine percent of the patients died of their disease on follow-up. On whole-exome sequencing, pathogenic/oncogenic alterations were identified in 91% (32/35) cases. These alterations, most frequently involved chromatin modifiers (66% cases), including ATRX , KMT2C , ARID1A , and ARID1B . Other frequently mutated genes included ATM , NF1 , and ERBB2 . Ninety-seven percent (34/35) of cases were microsatellite stable, and tumor mutational burden (TMB) was >10 mut/Mb in 9% (3/35) of cases. Five cases were homologous recombinant-deficient on ScarHRD analysis, and 3 cases showed BRCA mutations. Recurrent copy number loss events in Chr 1(p36.33-p35.3) were the most common copy number alterations (80%; n=28 cases). RNA-sequencing data analysis revealed numerous differentially expressed genes and enrichment of the epithelial-to-mesenchymal transition gene signature in individual samples. However, there was no statistical significance in the progression-free survival between cases with epithelial and mesenchymal phenotypes. CCA-UT are aggressive tumors with a heterogeneous molecular profile, underscoring the role of molecular analysis in identifying potential therapeutic options for the treatment of this pernicious tumor.