Pet Cancer: Understanding Hemangiosarcoma in Dogs and Cats

Labrador Retrievers, Golden Retrievers, Boxers and German Shepherds are at higher risk for developing hemangiosarcoma.

Hemangiosarcoma strikes like a lightning bolt. One minute your pet is fine and the next, he has collapsed from internal bleeding. As an oncologist, I rarely see this tumor until after the emergency room has corrected the internal hemorrhage via surgery and the biopsy report comes back. Because hemangiosarcoma is not an uncommon tumor, especially for some popular breeds of dog, here are some facts you ought to know.

What Is Hemangiosarcoma?

Cancer is an uncontrolled proliferation of cells that have the potential to spread throughout the body. We often think of cancer as arising from various organs in the body: breast cancer, colon cancer, skin cancer. Hemangiosarcoma is a malignancy originating in an organ system we don’t think much about: the circulatory system, and specifically, blood vessels. The name of this tumor comes from the Greek word for blood vessel, hemangio, and sarcoma, the word for a malignancy derived from connective tissues like blood vessels.

Where Does It Occur?

Hemangiosarcoma arises from the highly specialized delivery system for blood. Since blood vessels are located all over the body, this cancer can — and does — develop everywhere. Despite the widespread nature of blood vessels, there are specific sites in the body where this cancer is most likely to occur: spleen, liver, heart and skin. Because hemangiosarcoma is a malignancy, meaning that it can invade and destroy nearby tissue and metastasize to other sites, this cancer can rapidly spread diffusely throughout the body — often before we can detect the presence of the tumor. For this reason, it is not one of my favorite tumors.

What Are the Signs?

Pets with hemangiosarcoma may look deceptively normal until one of the cancerous blood vessels in the tumor ruptures. Then, in a heartbeat, your pet can go from looking normal to being in a state of collapse and shock. Blood can build up in the abdomen if the tumor arises from the spleen or liver and around the heart if the tumor arises from that organ. In either case, massive hemorrhage from the tumor’s abnormal blood vessels makes life-saving emergency surgery to remove the bleeding tumor a necessity in many cases.