Tumors of the spleen are called hemangiosarcomas or hemangiomas. Eighty percent of all splenic tumors are malignant, or hemangiosarcomas. Twenty percent are hemangiomas, which are benign. Hemangiosarcomas are highly malignant tumors of the blood vessels in the spleen.

The spleen is an organ in the abdomen that stores red blood cells. It is also involved in producing cells that assist in our immune system. Growth of a mass on the spleen may go undetected until it becomes quite large or ruptures, which may result in life-threatening bleeding into the abdomen. Hemangiosarcomas have a high propensity to metastasize quickly to other organs such as the heart, lungs and liver. Dogs at risk include middle-age to older large-breed dogs, especially Labrador retrievers, golden retrievers, and German shepherd dogs, though all breeds are susceptible.

The reason this tumor develops is unknown. Hemangiosarcomas can develop in any tissue that contains blood vessels. The most common sites include the skin, spleen and heart. Clinical signs are usually related to internal bleeding that arises from rupture of the splenic mass. Signs usually include sudden weakness or collapse, pale gums, abdominal distention and elevated heart and respiratory rates from shock. The bleeding can be life-threatening and can result in death if untreated.

It is not often possible to determine from routine tests whether the tumor of the spleen is benign or malignant, so biopsies are commonly done at the time of surgery after removing the mass. Dogs and people can live without their spleen, so a splenectomy removes not just the mass but the whole spleen.

If no evidence was uncovered that the tumor had spread, then removal of the mass and the spleen may be a good treatment option to stop the bleeding episodes. But surgery is not considered a cure for hemangiosarcoma, because it is a highly malignant disease and usually spreads to other sites in the body. If the mass is benign, surgery will be curative and eliminate the risk of ongoing blood loss.

Once the diagnosis of hemangiosarcom is made by histopathology, chemotherapy may be considered to slow the spread of disease to other body systems.

Hemangiosarcomas is an aggressive cancer with a survival time of one to four months with surgery alone. Additional chemotherapy improves survival times. Removal of the spleen spares the patient sudden death from a bleeding episode, but almost all animals eventually succumb to the cancer.

Dr. Karsten Fostvedt is a veterinarian at St. Francis Pet Clinic in Ketchum.

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