Hemangiosarcoma is a tumor of blood vessels. This tumor occurs more frequently in dogs than any other species and tumors are most commonly seen in the spleen, skin, and heart. Cutaneous hemangiosarcoma can be caused by sun exposure, especially in dogs that sunbathe (e.g. sight-hounds, bulldogs, and pit bull terriers). Although this type of hemangiosarcoma can be cured with surgery, further tumors can develop. Therefore, affected dogs should avoid sun exposure and be monitored for new tumors. At all other sites in the body hemangiosarcoma is aggressive, spreading rapidly throughout the body. Also, because hemangiosarcoma is a tumor of blood vessels, tumor rupture is common resulting in potentially life-threatening blood loss. Breed predispositions for hemangiosarcoma include German shepherd dogs, golden retrievers, and Labrador retrievers. Currently, surgery, chemotherapy (including standard and more novel protocols designed to target tumor blood vessels), and occasionally radiation therapy are used to treat dogs with hemangiosarcoma. Unfortunately, even with aggressive therapies, for hemangiosarcoma of the spleen, heart, and muscle average survival times are less than 1 year. Researchers are currently studying genetic factors to provide early diagnosis and to serve as targets for new therapies; it is suspected that these same factors are associated with vascular tumors in people. The CCOGC plans to assist these and future studies by providing samples from dogs with hemangiosarcoma.