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Cancer Treatment / LEARNING CURVE


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not available to obtain accurate estimates of risk and incidence in companion ani- mals, hemangiosarcoma appears to be relatively common in dogs, unlike its counterpart in humans, commonly called angiosarcoma, which is vanishingly rare (less than .01% of human tumors). Reports of canine hemangiosarcoma


are traceable to the early 1960s in the current medical literature. By the mid- 1970s, Priester had recognized that hem- angiosarcoma of the liver occurred 25 to 100 times more frequently in dogs than in humans (Priester 1976), and by the late 1970s various investigators noted a breed predilection in German shepherd dogs in Europe (Appleby et al. 1978). The breed predilection for hemangio-


sarcoma was confirmed and extended through various retrospective studies in the United States in the 1980s and 1990s (Prymak et al. 1985). Seminal work from Priester and McKay published as a National Cancer Institute monograph in 1980 provided the first reasonable esti- mate for the occurrence of hemangiosar- coma in domestic dogs in North America (Priester and McKay 1980). Splenic hem- angiosarcomas accounted for approxi- mately .3% of all tumors. Several of the common breeds we


now associate with this disease, includ- ing boxers and golden retrievers, were already overrepresented in the affected population of this systematic survey. Notably, Priester and McKay reported no significant differences in risk between male, female or neutered animals. Argu- ably, the larger prevalence of sexually intact animals in that era might provide more accurate numbers to assess the potential effect of neutering on a dog’s risk to develop this disease. The common primary sites for hem-


angiosarcoma are the spleen, the right atrium of the heart, the liver and the sub- cutis. The pattern of growth involves infil- tration into normal tissues surrounding the tumor as well as distant metastasis. Yet, the disease is insidious; that is, it does not cause pain, and the rate of growth in


Hemangiosarcoma is perhaps the most aggressive vascular tumor diagnosed in dogs.


the early stages is relatively slow. Dogs harboring even large hemangio-


sarcomas may show no clinical signs or evidence that they have a life-threaten- ing disease. Generally, tumor-associated blood vessels are tortuous and malformed, and blood cells tend to pool in them and clot. The clots prevent blood and nutrients from reaching tumor cells, in turn causing these cells to die. This creates small rup- tures in the tumor through which blood may escape into the abdomen, heart sac, chest or subcutaneous space. Depending on the amount of blood


lost, affected dogs may show constitu- tional signs, including lethargy and weak- ness, but these are transient and resolve as dogs reabsorb the blood components and make new blood cells. The clinical signs are recurrent, but they also are subtle enough to go unnoticed for some time. Microscopic, if not macroscopic,


Trends magazine, April 2013


Jaime Modiano, VMD, PhD, examines a golden retriever at the University of Minnesota College of Veterinary Medicine. Golden retrievers have a high incidence of cancer.


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