Stage III splenic hemangiosarcoma means the cancer has already visibly spread beyond the spleen at the time of diagnosis, most commonly to the liver, omentum (a fatty tissue drape in the abdomen), lungs, or peritoneum. This carries a grave prognosis because the cancer is no longer confined to a single removable site. The underlying biology is the same as earlier stages — a malignancy of the blood vessel lining cells — but with established secondary tumours in vital organs. Treatment at this stage is primarily palliative, aimed at controlling symptoms and maintaining quality of life rather than seeking a cure. Decisions about splenectomy and chemotherapy at this stage weigh potential survival benefits (typically weeks to a few months) against treatment burden and quality of life.