Comparison of BEAMing and Droplet Digital PCR for Circulating Tumor DNA Analysis

Circulating tumor DNA (ctDNA) assays are increasingly used for clinical decision-making, but it is unknown how well different assays agree. We aimed to assess the agreement in ctDNA mutation calling between BEAMing (beads, emulsion, amplification, and magnetics) and droplet digital PCR (ddPCR), 2 of the most commonly used digital PCR techniques for detecting mutations in ctDNA. Baseline plasma samples from patients with advanced breast cancer enrolled in the phase 3 PALOMA-3 trial were assessed for and mutations in ctDNA with both BEAMing and ddPCR. Concordance between the 2 approaches was assessed, with exploratory analyses to estimate the importance of sampling effects. Of the 521 patients enrolled, 363 had paired baseline ctDNA analysis. mutation detection was 24.2% (88/363) for BEAMing and 25.3% (92/363) for ddPCR, with good agreement between the 2 techniques (κ = 0.9l; 95% CI, 0.85-0.95). mutation detection rates were 26.2% (95/363) for BEAMing and 22.9% (83/363) for ddPCR, with good agreement (κ = 0.87; 95% CI, 0.81-0.93). Discordancy was observed for 3.9% patients with mutations and 5.0% with mutations. Assessment of individual mutations suggested higher rates of discordancy for less common mutations ( = 0.019). The majority of discordant calls occurred at allele frequency