PIK3CA and malignant colon neoplasm: To ascertain the dependence of MEK inhibitors on β-catenin, we investigated the effect of β-catenin silencing via small interfering RNA (siRNA) on MEK inhibitor-treated colon cancer cells that express mutant PIK3CA. We used a single siRNA sequence for β-catenin knockdown, which was analysed by a BLAST programme and confirmed for its specificity to β-catenin.