Hemangiosarcoma

Hemangiosarcoma is a cancer of blood vessel walls that grows most often in the spleen or heart, where it can bleed with no warning. In the Golden Retriever Lifetime Study, more than 7 percent of over 3,000 dogs had been diagnosed by a median age of about eight, and almost 90 percent of those tumours were internal¹. The German Shepherd Dog is also widely reported as predisposed².

The disease is usually silent until a bleed. The signs of a bleed are sudden weakness or collapse, pale gums, a swollen belly, rapid breathing, and then a recovery over a day or so as the blood is reabsorbed, which can make the episode easy to dismiss. Any collapse in a senior dog of an at-risk breed is a same-day emergency, and pale gums are the thing to check.

Ask your vet about periodic abdominal ultrasound and heart screening in the highest-risk breeds. Treatment is surgery, sometimes with chemotherapy; the outlook depends on how far the cancer has spread, and the conversation is an honest one¹².

This is general information, not a diagnosis. Your vet knows your dog.

Sources

1. Descriptive analysis of haemangiosarcoma occurrence in dogs enrolled in the Golden Retriever Lifetime Study (Hillman et al.). Veterinary and Comparative Oncology, 2023 (peer reviewed). Accessed 2026-09-22.
2. Breed-Predispositions to Cancer in Pedigree Dogs (Dobson JM). ISRN Veterinary Science, 2013 (peer reviewed review). Accessed 2026-09-22.