TDO2 and melanoma: In most cancers, such as glioblastomas, melanomas, colon carcinomas, lung carcinomas, and endometrium carcinomas, TDO could be detected in pericytes that belonged to morphologically abnormal vessels in the intratumoral rather than tumor cells themselves (62), although the mechanism that triggers TDO expression in tumor pericytes and the relationship between TDO-expression pericytes and abnormal vessels are all unclear, which suggests that TDO may play a proangiogenic role depending on its expression site in certain cancer types.