Siphonaxanthin is a carotenoid found in green algae, known for targeting the death receptor 5 (DR5) on cancer cells to induce apoptosis. In human leukemia HL-60 cells, it increases DR5 expression, reduces Bcl-2 levels, and activates caspase-3. It also inhibits fibroblast growth factor receptor-1 (FGFR-1) signaling in endothelial cells. Siphonaxanthin suppresses the proliferation, migration, and tubular formation of human umbilical vein endothelial cells (HUVECs), as well as the growth of microvessels in rat aorta rings. Additionally, it has anti-inflammatory properties by blocking the translocation of high-affinity IgE receptors (FcεRI) to lipid rafts in mast cells. Siphonaxanthin shows potential for research into diseases such as cancer, diabetic retinopathy, and rheumatoid arthritis.