However, As2O3, a Gli inhibitor that has been shown to inhibit Hh activity by decreasing Gli expression [25, 26], is unable to affect PGE2-provoked Hh activity, in despite of obvious inhibitory effect on the proliferation of colorectal cancer cells, possibly due to the its induction of apoptosis of cancer cells [31, 32]. This evidence concerns the gene GLI1 and cancer.