Genomic Landscape of Young-Onset Bladder Cancer and Its Prognostic Implication on Adult Bladder Cancer

Bladder cancer is common in elderly men, and it is a highly mutated tumor with frequent TP53 and FGFR3 mutation. Young-onset bladder cancer (YBC) is extremely rare; therefore, its genomic characteristics are unknown and appropriate management strategy is yet to be defined. Through a nation-wide search for bladder cancer diagnosed at 20 years or younger, 29 cases of biopsy-proven YBCs were collected. Whole exome sequencing and RNA sequencing were performed on 21 and 11 cases, respectively, and the results were compared with those of adult bladder cancer (ABC) retrieved from public database. Almost all YBCs were low grade, non-invasive papillary tumors. YBC had low mutation burden and less complex copy number alterations. Driver mutations were found in all cases. Common mutations included HRAS mutations (10 cases) with a preference in exon 5 and FGFR3 gene fusions (7 cases) with various partner genes, which occurred in a mutually exclusive manner. Other alterations included KRAS mutations (2 cases), arm-level deletion of chromosomes 4p and 10q (1 case), and ERCC2 mutation (1 case). TP53 and FGFR3 point mutations were not found. The gene expression profiles of YBC corresponded to those of the good prognostic group of ABC. No YBC cases had progressed to muscle-invasive tumor during follow-up. In addition, ABCs with YBC-like mutations also showed no progression to muscle-invasive tumor. In conclusion, YBC had distinct driver genetic alterations such as HRAS mutation and FGFR3 gene fusion and showed good prognosis. YBCs and ABCs with YBC-like mutations may be managed with less aggressive surveillance. RNA expression matrix (FPKM values) derived from RNA sequencing of 11 young-onset bladder cancers Submitter note: According to my review of our national law and research IRB, my raw data disclosure is not allowed.