Hemangiosarcoma is an aggressive, malignant tumor derived from blood vessel cells that grows rapidly, can cause severe bleeding, and has a high metastasis rate. It most commonly affects the spleen but can also occur in the heart, skin, and liver, with certain breeds like German Shepherds, Golden Retrievers, and Labradors at higher risk. Treatment typically involves surgical removal followed by chemotherapy, though targeted therapies and supplemental approaches like metronomic therapy and mushroom extracts are showing promise. Despite aggressive conventional treatment, prognosis remains guarded, with median survival ranging from 1-7 months depending on tumor location and whether chemotherapy is pursued after surgery.