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Hemangiosarcoma (HSA) is an aggressive tumor of malignant endothelial cells. Hemangiosarcoma occurs more frequently in dogs than other species, representing 2% of canine cancer and up to 50% of canine splenic cancer. Clinical presentations range in severity from blood-filled dermal nodules to acute collapse (secondary to hemoperitoneum or cardiac tamponade). The metastatic potential and biologic behavior of hemangiosarcoma is also tied to the tissue of origin. Small, solar-induced cutaneous hemangiosarcoma can be cured with surgery alone, in contrast to the ruptured splenic masses (stage II), where splenectomy results in a median survival time of < 2 months.
Dogs with incidentally diagnosed splenic masses without hemoperitoneum are more likely to be benign than malignant (70.5% vs 29.5%). Hemangiosarcoma is the most common malignant cause of a splenic mass in dogs. To screen for metastatic disease, pre-surgical staging with chest X-rays and abdominal ultrasound is recommended. Ultrasound has a low reported sensitivity for detecting intra-abdominal metastasis beyond the liver and spleen, missing >80% of lesions preoperatively. Thoracic radiographs have the greatest sensitivity for detection of pulmonary metastasis when both lateral views are obtained. Cytologic samples are often limited due to the vascular nature of these tumors and secondary hemodilution. Histopathology is recommended for a definitive diagnosis. Median survival time with surgery alone is impacted by disease stage, ranging from 5.5 months (stage I) to 0.9 months (stage III). The addition of maximally tolerated dose chemotherapy can improve prognosis to approximately six months.
Cardiac hemangiosarcoma is often a presumptive diagnosis based on the presence of a mass associated with the right atrium or auricle. Staging with chest X-rays and abdominal ultrasound is recommended because concurrent splenic masses are reported in ~29% dogs with suspected primary cardiac HSA. Treatment options include surgery, radiation therapy, chemotherapy, or palliative supportive care. Surgery is an option for tumors arising from the right auricle, but median survival time is still < 4 months due to the metastatic nature of this tumor. Radiation therapy can be considered for cases in which surgical resection is not possible, and can help reduce the frequency of palliative pericardiocentesis. With the addition of chemotherapy post-surgery, median survival time of 5.8 months is reported. If general anesthesia isn’t feasible, treatment with doxorubicin-based chemotherapy alone has a response rate of 41% and a median survival time of ~4 months. Supportive medications commonly used in clinical practice are Yunnan Baiyao and aminocaproic acid, both of which are generally well tolerated but were not found to delay recurrence of clinical signs or improve survival in dogs with right auricular masses and pericardial effusion.
Compared to dogs, the data regarding feline hemangiosarcoma is limited. One of the largest retrospective case series included 53 cases (24 cutaneous, 17 subcutaneous, 10 visceral, two gingival). In 88% of cases, surgery was the primary treatment. Tumor location, tumor margins, and mitotic count were significantly associated with survival. Mitotic count >3/10 hpf were associated with shorter survival times.
Hemangiosarcoma is an aggressive cancer in dogs and cats, and the prognosis for visceral forms is generally poor. Surgery is indicated whenever possible (nonmetastatic single lesions), and doxorubicin-based chemotherapy can prolong life by delaying the formation of metastatic disease. New treatment combinations including immunotherapy and targeted agents are under investigation to improve the prognosis for these patients.
