Droplet digital PCR monitoring of BRAF and NRAS plasma DNA as biomarkers of treatment response in stage IV melanoma

9019 Background: Management of melanoma suffers from a lack of robust biomarkers of disease activity. In this study, we tested the ability of droplet digital PCR (ddPCR) to quantitatively measure levels of circulating BRAF and NRAS mutant DNA in the plasma of metastatic melanoma patients undergoing treatment with BRAF-targeted therapy or immunotherapy. Methods: We analyzed plasma samples from 45 patients with stage IV melanoma prospectively enrolled in the NYU Melanoma Biorepository program. All patients were commercially genotyped for BRAF V600E. SNaPshot assays were used to identify NRAS Q61 mutations in BRAF-WT tumors. Each patient had at least 3 serially collected plasma samples including one drawn prior to treatment, one or more after treatment began and one upon signs of disease progression. ddPCR was used to measure mutant copies/ml of BRAF V600E and NRAS Q61K/L/R DNA in plasma samples. Results: Among 45 patients, 28 patients had BRAF and 8 patients had NRAS tumor mutations. We extracted DNA from 1...