Hemangiosarcoma in Dogs
Introduction
Hemangiosarcoma (HSA) is a highly malignant and aggressive cancer that arises from the endothelial cells lining blood vessels. This cancer primarily affects dogs, especially larger breeds like German Shepherds, Golden Retrievers, and Labrador Retrievers. Commonly found in the spleen, heart, liver, and skin, HSA is notorious for its rapid progression, metastatic potential, and poor prognosis.
Incidence and Prevalence
HSA accounts for approximately 2% of all canine tumors, with the spleen being the most common primary site. The “double two-thirds rule” is often applied in diagnosis:
– Two-thirds of splenic masses are malignant.
– Of those, two-thirds are hemangiosarcomas.
Though HSA predominantly affects large-breed dogs, it can occur in any breed. Small-breed dogs are less likely to develop hemangiosarcoma, with 43% of splenic masses being malignant compared to 63% in large-breed dogs. The median age at diagnosis is typically around 10 years.
Clinical Signs and Presentation
Hemangiosarcoma often presents suddenly, as many dogs experience tumor rupture, leading to internal bleeding (hemoabdomen). Clinical signs can include:
– Sudden weakness or collapse
– Pale mucous membranes
– Lethargy
– Abdominal distension
– Rapid heart rate (tachycardia)
In cases where the heart is involved (cardiac HSA), fluid accumulation around the heart (pericardial effusion) can lead to signs of heart failure, such as muffled heart sounds and weak pulses. Cutaneous HSA may appear as bruised or blood-filled lesions on the skin.
Diagnosis
Diagnosing HSA often requires a combination of imaging and laboratory tests to confirm the presence of masses and assess the extent of the disease. Diagnostic tools include:
– Complete blood count (CBC): Often shows anemia and thrombocytopenia, which are common in HSA.
– Coagulation profiles: Assess for disseminated intravascular coagulation (DIC), which occurs in up to 50% of cases.
– Thoracic radiographs: Used to check for metastasis in the lungs.
– Abdominal ultrasound: The most commonly used imaging tool to detect splenic or liver masses, but its ability to distinguish between malignant and benign masses is limited, with a sensitivity of 41.9% and specificity of 51.2%.
– Echocardiography: Essential for diagnosing cardiac HSA, especially to assess fluid accumulation in the pericardium.
– CT (Computed Tomography) scan: A valuable tool for assessing the extent of metastasis and providing a more detailed view of the masses, especially for complex cases involving multiple organs. CT scans can help guide surgical planning and provide more information on tumor invasiveness.
Treatment Options
1. Surgery:
– Splenectomy is the primary treatment for splenic HSA, but surgery alone provides a median survival time of 1 to 2.5 months. When combined with chemotherapy, the survival period extends to 5 to 8 months.
– For cardiac HSA, surgery is usually palliative, and survival without chemotherapy is often limited to 2 weeks, while chemotherapy can extend survival to 4 months.
2. Chemotherapy:
– Doxorubicin is the most commonly used chemotherapy agent for HSA. It extends the median survival time to 5 to 8 months when used after surgery. Other chemotherapy protocols, such as the DAV Protocol (Doxorubicin, Vincristine, Dacarbazine), have shown a 47% response rate in advanced-stage HSA.
– Metronomic chemotherapy (low-dose cyclophosphamide with NSAIDs) has shown comparable median survival times to traditional chemotherapy regimens, around 6 months in some studies.
3. Radiation Therapy:
– Radiation therapy is typically reserved for cutaneous HSA, where it can be effective in treating superficial lesions. However, its use is limited for visceral HSA (affecting internal organs), as most commonly involved sites like the spleen, heart, and liver are located within the thoracic or abdominal walls, making radiation less feasible.
4. Novel Therapies:
– eBAT, an investigational targeted therapy, has shown promising results, extending median survival to 8.5 months in a small trial, with a 70% 6-month survival rate.
Prognosis
The prognosis for dogs with HSA is generally poor due to the aggressive nature of the disease and its high metastatic potential. Splenic HSA, even when treated with surgery and chemotherapy, has a 1-year survival rate of less than 10%. Cardiac and visceral forms of HSA tend to have even shorter survival times, often measured in weeks to a few months. Cutaneous HSA, however, can have a more favorable prognosis if detected and treated early, with median survival times exceeding 2 years for localized skin lesions.