Detection of cell-free circulating BRAFV600E by droplet digital polymerase chain reaction in patients with and without melanoma under dermatological surveillance

Background The p.V600E mutation in the BRAF protein is the most frequent mutation in cutaneous melanoma and is a recurrent alteration found in common benign naevi. Analysis of the cell-free BRAF c.1799T>A, p.V600E mutation (cfBRAF(V)(600E)) in plasma has emerged as a biomarker for monitoring prognosis and treatment response in patients with melanoma. Objectives To quantify cfBRAF(V)(600E) levels in plasma from patients with melanoma and from patients without melanoma undergoing regular follow-up of their melanocytic lesions, in order to assess the clinical significance of the test. Methods We quantified cfBRAF(V)(600E) by droplet digital polymerase chain reaction in plasma from 146 patients without melanoma undergoing continuous dermatological screening, from 26 stage III and seven stage IV patients with BRAF-mutant melanoma, and from 32 patients with melanoma who were free of disease for 3 or more years. Results Among disease-free patients and individuals without melanoma, 52% presented a high naevus count (> 50) and 49% had clinically atypical naevi. cfBRAF(V)(600E) was detected in 71% of patients with stage IV melanoma and 15% with stage III, and in 1 center dot 4% of individuals without melanoma. No cfBRAF(V)(600E) mutation was detected in disease-free patients with melanoma. Individuals without melanoma had lower cfBRAF(V)(600E) levels than patients with melanoma. We established a variant allelic frequency of 0 center dot 26% or 5 copies mL(-1) of cfBRAF(V)(600E) as the optimal cutoff value for identifying patients with melanoma with > 99% specificity. Conclusions This study suggests that naevus-related factors do not influence the detection of cfBRAF(V)(600E) in individuals without melanoma, and supports the clinical diagnostic value of plasma cfBRAF(V)(600E) quantification in patients with melanoma.