In conclusion, given the uncertain efficacy of IDO1 inhibitors together with immune checkpoint inhibitors in advanced melanoma and, based on our current results, demonstrating a direct effect of dex on TDO expression and function in human SK-Mel-28 melanoma cell line, it becomes of increasing importance to better characterize the involvement of the TDO pathway in melanoma tumorigenesis. Here, IDO1 is linked to melanoma.