With the online tool TIMER2.0 (http://timer.cistrome.org/ accessed on 12 January 2024), which is a server able to perform associations between immune infiltration and different tumor characteristics using data from The Cancer Genome Atlas (TCGA) [21], we performed an analysis which indicated that TDO expression positively correlates with the infiltration of endothelial cells in metastatic but not in primary melanoma (Figure 6). Here, TDO2 is linked to neoplasm.