Circulating cell-free DNA profiling of patients with advanced urothelial carcinoma

358 Background: Urothelial carcinoma (UC) exhibits one of the highest somatic mutation burdens. Circulating cell-free DNA (cfDNA) is obtained non-invasively from peripheral blood and appears detectable in most patients (pts) with advanced UC. We report cfDNA profiling of patients with advanced UC using biopsy-free cfDNA sequencing. Methods: Twenty-nine patients with advanced UC that underwent cfDNA analysis using Guardant360 were identified. A 68-gene cfDNA next generation sequencing (NGS) panel from a CLIA-licensed, CAP-accredited laboratory (Guardant360) offers complete sequencing for all exons in 29 cancer associated genes, as well as the critical exons in 39 other genes, and copy number amplifications (16), fusions (4) and indels (1) in selected genes, harvested from 20 mL of peripheral blood. The mutant allele fraction (MAF) is defined as the number of mutated cfDNA molecules divided by the number wild type cfDNA molecules at a given nucleotide position. Results: Of 29 patients with advanced UC, cfDNA was detectable in 25 patients (86.2%). Twenty-nine patients were available with bladder primary in 27 pts (93.1%), and the median age was 75 years (range 52-91). The most common recurrent somatic mutations in the 25 patients with ≥ 1 alteration were in TP53 (n = 17), BRCA1/2 (n = 6), FGFR2 (n = 5), EGFR (n = 5), PIK3CA (n = 4), APC (n = 4), KRAS (n = 4), RAF1/BRAF (n = 4), and FGFR3, ALK, PDGFRA, NF1, CDKN2A and ARID1A were observed in 3 patients each. The most common genes with ≥ 2 copy numbers in the 25 evaluable patients were ERBB2 (n = 2) and PIK3CA, EGFR, RAF1, and FGFR1 in one patient each. Analysis of additional patients is ongoing in this expanding dataset. MAF data will be presented. Conclusions: cfDNA is frequently detected in patients with advanced UC, and alterations appear similar to those previously reported from UC tumor tissue. The correlation of cfDNA profiling with tumor tissue profiling within patients and ability to predict response requires study. Given that cfDNA offers a non-invasive means of profiling tumor DNA and MAF, further development of this promising modality is warranted to guide therapy with biologic agents and immunotherapy, and serial monitoring may provide insights regarding tumor biology.