In addition, it has been demonstrated that HO-1 silencing sensitizes human urothelial as well as HeLa cervical cancer cells to 5-aminolevulinic acid-based photodynamic therapy [75,94] and that HO-1 siRNA or inhibition increase the PDT cytoxicity in colon adenocarcinoma C-26 and human ovarian carcinoma MDAH2774 cells [95]. This evidence concerns the gene HMOX1 and colon adenocarcinoma.