PIK3CA and colorectal carcinoma: Gene targeting of PIK3CA in the CRC cell line HCT116 revealed that exclusive expression of a PIK3CA allele harboring an activating H1047R substitution (HCT116 PIK3CA-mut) in exon 20 conferred resistance to TRAIL-induced apoptosis (Figure 1a).9, 10 In sharp contrast, the isogenic cell line with a wild-type PIK3CA allele (HCT116 PIK3CA-wt) died in a dose-dependent manner after TRAIL stimulation (Figure 1a; ED50-value ~10 ng/mL).