Since we already demonstrated the key role of TDO in different human melanoma cell lines and based on the observed positive correlation between TDO expression and endothelial cell infiltrations, we then investigated the possible role of TDO in endothelial cells’ behavior in the presence of malignant human melanoma cells SK-Mel-28 and A375, which have been reported to exhibit different levels of invasiveness [22]. The gene discussed is TDO2; the disease is melanoma.