ERBB2 and breast cancer: Digital PCR [16], most notably droplet digital PCR (ddPCR) [17], is an emerging technology that has been used to quantify CNAs within a genomic target (biomarker) [18], including gains in HER2 prognostic of breast cancer [19, 20] and in the fibroblast growth factor receptor 2 (FGFR2) associated with gastrointestinal tumors [18].