Dog That Collapsed While Running

History. A spayed, l()-year-old female golden retriever collapsed while running outside earlier today. The dog is still very lethargic and does not want to move.

Clinical Examination.

Comment. Based on this history and physical examina­tion, there is concern that this dog has hemorrhaged into the abdomen. Hemangiosarcoma is a common tumor of older dogs and originates from a transformed endothelial cell. Dogs often present after having collapsed when the tumor, which is present in the spleen, causes internal bleeding. The dogs must often have emergency surgery to have a splenectomy (spleen removed). In some cases, dogs may show other, nonspecific clinical signs (inappetence, lethargy), so a diagnosis may be made before the dog collapses from acute bleeding. A diag­nosis is often made through a combination of modalities, including radiographs, ultrasound, biopsies, histopathology, and immunohistochemistry, to determine the nature of the tumor. In many cases, by the time the diagnosis has been made, the tumor has already metastasized, usually via hematogenous route, to other organs. The lung and liver are more frequently affected, but other sites include kidney, muscle, brain, mesentery, skin, and lymph nodes. Recently it has been demonstrated that canine hemangiosarcomas express platelet-derived growth factor beta (PDGF-β). Suppression of this RTK signaling using imatinib (Gleevec) suppressed the canine cell line in a mouse model.

Treatment. Depending on the stage at which the tumor is diagnosed, as in this case, the animal presents with shock and hemorrhage. In these cases the patient is stabilized, surgery is performed, and the spleen (in this patient) is removed. The overall prognosis for these cases is poor because the tumor has usually metastasized by the time the initial diagnosis is made. Radiation therapy is palliative for these cases, and it is sometimes used when there is a large, local Unresectable mass. Chemotherapy is usually the treatment of choice, although median survival time for these dogs typically is not long. Medications often include the VAC protocol: doxorubicin, cyclophosphamide, and vincristine. Doxorubicin inhibits DNA synthesis, DNA-dependent RNA synthesis, as well as protein synthesis, and it acts throughout the cell cycle. Cyclophosphamide inhibits DNA replication as well as RNA transcription and replication. Vincristine binds to specific microtubular proteins to inhibit cell division. Complications

associated with chemotherapy include myelosuppression and sepsis. Experimental treatments arc still being tested and target endothelial cells, blocking adhesion factors and inhibiting growth factors associated with endothelial cell growth.