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Canine Splenic Hemangiosarcoma

By Lillie Davis | DVM, DACVIM (Oncology)

Hemangiosarcoma (HSA) of the spleen is a devastating cancer that affects many dogs. It is a cancer of the vascular epithelial cells (cells lining the blood vessels) that comprises roughly 7% of all cancer in canines. This tumor can occur from any site of the body that’s vascular but the most frequent locations in dogs are the spleen (40-50%), right atrium/heart (10-25%), and the skin (15%). Hemangiosarcoma of the spleen is the most common cancer of the spleen in dogs. Approximately two thirds of dogs with masses of the spleen will have a cancerous tumor and two thirds of those cancerous tumors are HSA. Recent studies have found that 63-70% of dogs presenting with spontaneous hemoabdomen (blood in the abdomen from a non-traumatic event) have HSA of the spleen.

Splenic HSA is highly aggressive such that it grows rapidly and is highly metastatic, meaning the chances of it spreading to other locations of the body at the time of diagnosis is very high (80%). This tumor can spread to anywhere in the body due to its close proximity to blood vessels (i.e. liver, lungs, brain, organs in the abdomen). Unfortunately, we do not know what causes or predisposes animals to develop this type of cancer but it is believed to have some genetic predisposition as German Shepherds, Golden Retrievers, and Labradors are overrepresented.

Most dogs presenting with this cancer are brought to their veterinarian by their owners on an emergent basis due to a range of nonspecific clinical signs such as: decreased appetite, weight loss, lethargy, increased/labored breathing, swelling of the abdomen, and acute collapse/weakness. These clinicals signs are due to the major hemorrhage that occurs when the mass in the spleen ruptures and subsequently bleeds. It isn’t uncommon for these episodes of weakness or collapse to be transient over a period of days or weeks due to the rupture of the mass and theorized reabsorption of the blood in the abdomen.

Surgical removal of the splenic mass by removing the entire spleen (splenectomy) is the primary method of treatment for almost all dogs with HSA of the spleen. Unfortunately, due to the aggressive biological nature of this tumor, prognosis for dogs with this tumor is poor even in the face of surgery and adjunctive therapies. With surgical intervention alone, the median survival time (median survival time is defined as the time period where 50% of patients are still alive; this means however that 50% of the patients are not alive at that time period) varies between one and two months. Survival times may vary depending on the stage of the tumor at the time of treatment.

Clinical staging is performed with various diagnostic tests such as blood work, chest x-rays, abdominal ultrasound, etc. These tests are performed to investigate whether or not a patient has evidence of spread of their cancer prior to owners deciding if they want to move forward with surgical treatment or additional therapies after surgery is performed.

After local tumor control is gained with surgical removal of the splenic mass, systemic chemotherapy is the next therapy that is recommended. The median survival time for dogs with splenic HSA that receive surgery and chemotherapy is approximately 4-6 months (compared to the 1-2 months with surgery alone). Unfortunately, all dogs end up passing away from metastasis or spread of their cancer to other organs, even if it is not overt at diagnosis when initially staging the patient.

Without pursuing surgery, the average survival time can be days to weeks, and is highly variable as cavitated splenic masses can rupture at any time and result in severe internal bleeding, which if not treated is often fatal.

There are many reported chemotherapy protocols for the treatment of HSA. Unfortunately, no single protocol appears to extend life expectancy beyond that of all the other protocols. Doxorubicin (Adriamycin) is the one chemotherapeutic drug shown to be most effective in the treatment of HSA. Studies have shown comparable survival times when this drug has been used alone or in combination with other drugs. When used alone, this drug is administered every three weeks for five treatments total, requiring visits with our oncology service at those times. Blood work is checked prior to giving each dose of chemotherapy and chest x-rays and abdominal ultrasound is also performed periodically to ensure the chemotherapy is effective for each patient.

A recent study has shown that the addition of metronomic chemotherapy (a constant low dose of chemotherapy) after a patient receives chemotherapies like doxorubicin, may extend survival times a bit longer.

It is important to note that chemotherapy does not lead to a cure, it is instead used with the intention of slowing cancer progression while providing a good quality of life. Although designed to kill rapidly dividing cancer cells, chemotherapy can inadvertently kill normal cells, as well, including those that line the intestines, bone marrow and hair follicles, as it targets rapidly dividing cells. Side effects can include vomiting and diarrhea, deceased white blood cell counts and occasionally, hair loss. The white blood cell count can result in infection. If your pet’s white blood cell count decreases, antibiotics can be prescribed prophylactically. With this said, less than 20% of our patients get sick (lethargy, vomiting, diarrhea, etc.) and less than 5% need to stay in hospital due to side effects of chemotherapy. Chemotherapy related deaths are reported in less than 1% of patients.

Overall, our veterinary patients tolerate chemotherapy better than what we may be used to seeing in people. Chemotherapy is generally very well tolerated and pets have a great quality of life while undergoing therapy. If intolerable side effects are experienced, the dosage of chemotherapy medications can be reduced, as the goal of chemotherapy in veterinary medicine is to increase quality, not quantity of life.

In addition to traditional chemotherapy, recent clinical trials at the University of Pennsylvania have shown efficacy of I’m-Yunity mushroom supplements. I’m-Yunity is an extract of polysaccharopeptide from the Coriolus versicolor mushroom, known commonly as the Yunzhi mushroom. Clinical trials at the University of Pennsylvania have shown that I’m-Yunity in conjunction with splenectomy can result in similar survival times equivalent to the median survival time for animals that receive doxorubicin in conjunction with splenectomy. However this information must be taken with a grain of salt given the small number of cases in this study. I’m-Yunity may be purchased from the website There are currently no reported side effects, however the clinical trials have been small and side effects have not been studied in depth.

Many oncologists are also prescribing the Chinese supplement Yunnan Baiyao, which helps slow down or stop hemorrhage from leaking cancerous vessels. This supplement may also promote healing. Yunnan baiyao has been shown to kill hemangiosarcoma cells in laboratory experiments. Yunnan baiyao appears to help dogs anecdotally, but full clinical trials of the supplement and its effect on dogs with hemangiosarcoma are still in progress and so true efficacy and side effects are not currently known.