Hemangiosarcoma is an aggressive cancer of blood vessel cells in dogs, often discovered only when a tumor ruptures causing acute internal bleeding and collapse.
Hemangiosarcoma causes sudden, catastrophic hemorrhage when tumors rupture without warning. Dogs that appeared healthy hours before can die in acute collapse. Surviving emergency surgery face a median prognosis measured in months. The insidious pre-rupture phase may involve subclinical chronic blood loss causing fatigue and weakness that owners attribute to aging. Improved screening tools offer the possibility of earlier detection when treatment is more effective.