CD274 and cancer: Angiosarcoma, a rare and aggressive cancer that arises from the endothelial cells of blood or lymphatic vessels, often has a poor prognosis.1, 2, 3 Treatment includes surgery, radiation, or chemotherapy, yet these modalities have shown limited improvement in patient survival.4, 5, 6 Immunotherapy, targeting proteins such as the programmed cell death protein (PD-1) and its ligand, PD-L1, has emerged as a promising option.7