Microarray-based Analysis of the BRAF V600 Mutations in Circulating Tumor DNA in Melanoma Patients

Background: Circulating tumor DNA (ctDNA) holds great potential for cancer therapy and can provide diagnostic and prognostic information before and during treatment. Methods: Plasma DNA samples from 97 melanoma patients, 20 healthy donors and 3 patients with benign skin tumors were analyzed by microarray analysis and droplet digital PCR (ddPCR). Results: A microarray for simultaneous detection of six BRAF V600 mutations in ctDNA has been developed. The method allows the detection of 0.05% mutated DNA from WT DNA background. For paired samples (pre-surgery plasma and tumor tissue) isolated from 74 patients, the concordance of genotypes between tumor DNA and ctDNA was 65% (48/74). BRAF mutations in ctDNA were detected in 27/50 patients with BRAF-positive tumors and in 3/24 patients with BRAF wild-type tumors. The presence of ctDNA BRAF mutations in 23 plasma samples from melanoma patients undergoing therapy correlated significantly with tumor progression (P=0.005). The increase in cell-free DNA levels measured by ddPCR also correlated with disease progression (P=0.02). The concordance of results obtained by microarray identification of BRAF mutations and those obtained by ddPCR was 91%. Conclusion: The novel microarray-based approach can be a useful non-invasive tool for accurate identification of ctDNA BRAF mutations to monitor disease progression.