Low Frequency Kras G12/13 Mutations In Urine Cell-Free (Cf) Dna From Patients With Braf V600e-Mutant Advanced Cancers.

11048 Background: Tumor heterogeneity and clonal selection contribute to resistance to molecular targeted therapies. Dynamic tracking of urine cfDNA mutations can offer a noninvasive tool for monitoring therapeutic efficacy. Methods: cfDNA was isolated from single or sequential urine samples from patients with advanced cancers and archival tumor tissue with BRAF V600E from a CLIA-certified laboratory. Assays for quantitative detection of BRAF V600E and KRAS G12/13 mutations in urine cfDNA were developed using digital droplet (dd) PCR and next generation sequencing. Analytical sensitivity of BRAF V600E and KRASG12/13 assays is 0.03% and 0.006% mutant alleles in wild-type DNA background. Results: Urine cfDNA was examined in 34 patients (melanoma, n = 11; colorectal cancer, n = 8; papillary thyroid carcinoma, n = 5; non-small cell lung cancer, n = 5; other, n = 5) with BRAF V600E in tumor tissue. 32 of 34 patients (94%) had the same mutation in urine cfDNA (mutant, n = 22; low-mutant, n = 10). Longitudinal a...