This underpinned the results obtained by RT-PCR on tumor samples, which revealed that TDO is expressed in numerous human tumors, especially in hepatocellular carcinoma, bladder carcinoma, melanoma and glioblastoma, as well as in tumor lines, including glioblastoma, colorectal, head and neck and bladder carcinoma cell lines (Opitz et al., 2011; Pilotte et al., 2012). This evidence concerns the gene TDO2 and neoplasm.