Droplet digital PCR of the diffuse large B cell lymphoma formaldehyde-fixed paraffin-embedded tissue showing presence of myeloid differentiation factor 88 L265P mutant droplets (blue droplets, Ch1+/Ch2-). (A) Mutation frequency <10%; (B) mutation frequency <50%; (C) mutation frequency ≥50%. Ch1, mutation copy number; Ch2, wild-type copy number; Ch1+Ch2, genomic DNA copy number; Ch1/(Ch1+Ch2), mutation frequency. Green droplets depict wild-type droplets (Ch1-/Ch2+) region; gray droplets depict negative droplets without detectable DNA (Ch1-/Ch2-) region; orange droplets depict double positive droplets (Ch1+/Ch2+) region. Result judgment: i) Positive, mutation frequency ≥1% and ≥3 droplets fall in the ‘Ch1+Ch2-’ region; ii) Negative, <3 droplets fall in the ‘Ch1+’ region and <5 droplets fall in the ‘Ch2+’ region.