Molecular intricacies of upper tract urothelial carcinoma and their relevance for therapy considerations.

PURPOSE OF REVIEW: The aim of this study was to give an overview of molecular alterations in upper tract urothelial carcinomas (UTUCs) and to discuss them in the context of current and prospective systemic therapies. RECENT FINDINGS: UTUCs not only share a similar molecular landscape with urothelial carcinoma of the bladder (UCB), but also have distinct molecular features that can have an impact on therapy selection. FGFR3 alterations occur with a significant higher frequency in UTUC, with up to 40% of tumours harbouring FGFR3 driver mutations compared with 20% in UCB. In addition, a substantial number of high-grade UTUC show an immune-depleted phenotype and a luminal papillary expression subtype, thus predisposing them for FGFR inhibitor treatment. Approximately 20% of UTUC tumours have acquired mutations in TP53 and demonstrate a significant degree of genomic instability, which makes them candidates for systemic chemotherapy or immunotherapy. Whereas microsatellite instability (MSI) is rare in sporadic UTUC, 5-10% of UTUC patients have germline mutations in DNA mismatch repair genes, which leads to high MSI with enriched neoantigen load and presumably better response rates to immunotherapy. SUMMARY: Treatment decisions in UTUC should take molecular tumour characteristics into account. The currently most therapy-relevant molecular alterations in UTUC comprise FGFR3 mutational status and mutations in DNA mismatch repair genes with concomitant microsatellite instability.