EVT801 is an orally active, selective VEGFR-3 inhibitor (IC 50 = 11 nM) with demonstrated antitumor properties. It effectively suppresses VEGF-C-induced human endothelial cell proliferation and tumor (lymphatic) angiogenesis in mouse models. Moreover, EVT801 reduces tumor hypoxia and the production of immunosuppressive cytokines (CCL4, CCL5) and myeloid-derived suppressor cells (MDSC), enhancing the efficacy of immune checkpoint therapy (ICT). This synergy results in improved ICT response rates and more potent anticancer effects in cancer mouse models.