Representative image of PIK3CA exon 20 (A, B) and exon 9 mutations (C) using direct sequencing and digital PCR.

For the digital PCR assay, signals from wild-type-specific probe are detected as blue, and signals from mutant-type are detected as red. A; mutation is detectable by direct sequencing and harbors more than 50% of mutant DNA using digital PCR. B, C; detection of mutation is difficult by direct sequencing alone, harbors around 20% of mutant DNA by digital PCR.