Clinical utility of plasma ctDNA sequencing in metastatic urothelial cancer

Background: Genomic stratification may help improve the management of patients with metastatic urothelial cancer (mUC), given the recent identification of targetable alterations. However, the collection of tissue samples remains challenging. Here, we assessed the clinical utility of plasma circulating tumour DNA (ctDNA) sequencing in these patients.Methods: Patients with mUC were prospectively enroled in the STING trial (NCT04932525), in which ctDNA was profiled using the Foundation One Liquid CDx Assay (324 genes, blood tumour mutational burden [bTMB], microsatellite instability status). Each genomic report was reviewed by a multidisciplinary tumor board (MTB).Results: Between January 2021 and June 2022, 140 mUC patients underwent molecular profiling. The median time to obtain the assay results was 20 days ((confidence interval) CI95%: [20,21]). The ctDNA analysis reproduced the somatic genomic landscape of previous tissue-based cohorts. Concordance for serial ctDNA samples was strong (r = 0.843 CI95%: [0.631-0.938], p < 0.001). At least one actionable target was detected in 63 patients (45%) with a total of 35 actionable alterations, including bTMB high (>= 10 mutations/Mb) (N = 39, 21.1%), FGFR3 (N = 20, 10.8%), and Homologous recombination deficiency (HRD) alterations (N = 14, 7.6%). MTB recommended matched therapy in 63 patients (45.0%). Eight patients (5.7%) were treated, with an overall response rate of 50% (CI95%: 15.70-84.30) and a median progression-free survival (PFS) of 5.2 months (CI95%: 4.1 - NR). FGFR3 alterations were associated with a shorter PFS in patients treated with immunotherapy.Conclusion: Overall, we demonstrated that genomic profiling with ctDNAs in mUC is a reliable and feasible approach for the timely initiation of genotype-matched therapies.