Hemangiosarcoma in Cats: Causes, Symptoms, & Treatment

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Hemangiosarcoma is a very rare form of cancer in cats. But when it occurs, it tends to be very aggressive and can spread easily. In this article you’ll learn about the different forms of hemangiosarcoma we see in cats, how it’s diagnosed and treatment options.

Other Names: HSA

(Cutaneous/subcutaneous): bumps or growths on the skin with a red, blue, purple or combination appearance. (Visceral): lethargy, decreased appetite, pale gums, abdominal discomfort

Requires Ongoing Medication: Chemotherapy is one long-term option in cases where hemangiosarcoma is surgically removed.

Vaccine Available: No

Treatment Options: Surgery is initially the treatment of choice, especially for single lesions. Chemotherapy is a common recommended follow up to slow down recurrence and spread of this cancer.

Home Treatment: If your cat has visceral hemangiosarcoma, assessing appetite, energy, and gum color daily is vital for knowing when your cat needs to be rechecked. Regular health screening at your vet may help detect the presence of some forms of hemangiosarcoma early

What is Hemangiosarcoma?

Hemangiosarcoma (HSA) is a rare form of cancer in cats. Fortunately, it is estimated to affect only about 1-2% of cats at the most. Hemangiosarcoma affects cells called endothelial cells. Endothelial cells make up the lining of blood vessels.

Because blood vessels exist all over the body, hemangiosarcoma can in theory appear anywhere in the body. This also makes it very easy for hemangiosarcoma to spread throughout the body via blood vessels to other organs and locations.

But even though it can occur anywhere, there are still patterns we see more specifically in dogs and cats in terms of where it most often happens and behaves. In dogs, the most common primary locations are the spleen and the right atrial region of the heart.

But cats, have their own patterns which are very different from what we see in dogs.

Here are the most common forms in cats and what they look like.

Cutaneous/Subcutaneous

While the cutaneous and subcutaneous tissue layers of the skin are separate, they are often lumped together when it comes to research on hemangiosarcoma in cats.

This form is considered to be the most common in cats, though some suspect they may just be diagnosed more often since they are more visible than internal tumors. Tumors on the surface of the skin (cutaneous) are going to be the best scenario for surgical removal. Subcutaneous tumors carry a higher risk of spread (metastasis) and can be harder to remove completely with surgery.

Also lumped into this group is HSA which affects the eyes. HSA in the conjunctiva (the tissue below the eyelids) and third eyelid has occurred in cats as well as on the corneal surface.

Visceral

Visceral refers to organs. In cats, the spleen, liver, and intestinal tract are the most common sites where hemangiosarcoma is found. Other locations include lymph nodes, the omentum (tissue connecting intestinal loops in the abdomen), and the lungs. The pancreas has also been documented but is considered a rare location.

There is some disagreement about whether visceral HSA is actually less common than cutaneous/subcutaneous or whether it’s simply harder to diagnose. But there is general agreement that visceral is generally more aggressive and spreads more quickly.

Oral

There is very little data on how common oral hemangiosarcoma is, but compared to other oral tumors in cats, it is considered extremely rare. Squamous cell carcinoma accounts for up to 80% of oral tumors in cats with up to another 20% being fibrosarcoma. There are several other tumor types that make up the remaining small percentage of oral tumors and HSA is just one of them.

Causes of Hemangiosarcoma in Cats

Compared to dogs, there is very little overall data on feline hemangiosarcoma. Any kind of specific cause and effect for it is poorly understood, at least for visceral forms of HSA. As with many forms of cancer, combinations of both genetic and environmental factors likely play a part. There is no evidence that there is a higher risk in either males or females.

But for cutaneous/subcutaneous forms, there is evidence to support that sun exposure may be a contributing factor based on the locations where HSA is found in cats.

The most common locations for HSA on a cat’s skin include the scalp, ears, conjunctiva of the eyes, and muzzle. The flank and groin area have also been documented. These are all areas in cats that tend to get heavier sun exposure.

Squamous cell carcinoma is by far the most common malignant skin cancer in cats with connections to sun exposure. But the same risk factors for SCC in cats would appear to be present for cutaneous HSA.

Similar to the risk for SCC, cats with lightly pigmented skin, especially at the most common risk sites, are presumed to be at higher risk of developing cutaneous HSA in those areas.

Symptoms of Hemangiosarcoma in Cats

Assessing gum color can be one way to screen for the potential of internal bleeding, where the gums would appear much more pale or white compared to this image. RJ22 / Shutterstock.com

Hemangiosarcoma is seen more often in older cats, with the average being about 10 years of age.

Here are the most common signs/symptoms of hemangiosarcoma based on the location where it occurs.

Cutaneous

• Tumors are often small (0.1cm up to 1.0cm).
• Tumors have a red or purple colored appearance.
• Tumors most often occur on the head.
• Tumors most often occur in light-pigmented areas of skin.
• Tumors are usually not painful when touched.
• Skin surface tumors usually disrupt fur growth in their location (as opposed to subcutaneous).

Subcutaneous

• Tumors may be of similar size to cutaneous (0.1-1.0cm)
• These will appear more as a swelling just beneath the skin.
• Surface fur is usually not disrupted.
• These may appear more as a purplish blue appearance, similar to a bruise or hematoma.
• Location on the body appears to be similar to cutaneous tumors.

Ocular

• Most common sites are the conjunctiva (beneath the lid), third eyelid, and cornea.
• Appears as a focal red fleshy type growth on the eye.
• Conjunctival growths may appear more as a focal eyelid swelling or where the eyelid appears “pushed out” because of the growth occurring beneath it.

Oral

Oral tumors can be very difficult to visually see in cats, even during a veterinary exam. In many cases, oral tumors can occur beneath the tongue or further back into the mouth where it’s hard to see. When a cat is showing signs of significant oral pain or discomfort, sedation is often needed to get a thorough assessment.

These are general signs where there is enough oral pain or discomfort for an oral tumor to be a potential concern:

• Excessive salivating or drooling
• Blood present in saliva or drool
• Chewing food with one side of the mouth
• Dropping food while eating
• Excessive swallowing or tongue movement
• Reduced to absent appetite (may be gradual or appear suddenly)
• Weight loss
• Signs of pain, tensing, or irritation even with gentle attempts to handle mouth or face
• Pawing at the mouth
• Foul breath odor

Visceral

Unfortunately, in many cases, visceral hemangiosarcoma goes undetected until a bleeding crisis occurs. As a tumor that affects blood vessels, bleeding complications are very common with hemangiosarcoma. This is especially true when HSA affects the spleen.

The most common symptoms of visceral therefore are less specific, but associated with the effects of bleeding and abdominal discomfort:

• Lethargy/weakness
• Poor appetite
• Vomiting (may occur when a tumor ruptures/breaks open and starts bleeding)
• Rapid or labored breathing
• Collapse
• Pale gums
• Sensitive or tense abdomen
• Bloated or swollen-looking abdomen
• Cats with HSA in their intestinal tract may have signs of blood in vomit or stools.

Sadly, sudden death may be the only sign of visceral HSA in cats. This was documented in one particular 15-year-old cat with no history of weight loss or other signs of illness who had pancreatic HSA with spread to multiple sites in the abdomen.

Complications of Having Hemangiosarcoma in Cats

Metastasis, or the spread of cancer through blood and lymphatic vessels to other parts of the body, is the most common complication of hemangiosarcoma. Visceral HSA has the most metastatic potential because it is harder to diagnose early compared to cutaneous/subcutaneous HSA.

Spread to other areas of the abdomen is most common, but spread to the lungs is also possible. About 30% of cats in one study already had spread to the lungs at the time they were diagnosed with visceral HSA.

Bleeding is also a common complication. This is less of a risk for hemangiosarcoma on the skin, as bleeding will tend to be limited if it occurs. The highest risk of internal bleeding is associated with visceral HSA, especially in major organs like the spleen, liver, pancreas, and kidneys.

Diagnosis of Hemangiosarcoma in Cats

It can be very difficult to confirm hemangiosarcoma as a tumor type without a tissue biopsy. In dogs, hemangiosarcoma is one of the most common tumors associated with the spleen and heart, making it a presumptive diagnosis in many cases based on X-ray or ultrasound imaging.

But in cats, there are many other tumor types that are more common to find both on the skin, in the mouth, or in the abdomen.

Fine-needle aspiration to collect cell samples is one step below a biopsy. It can be used to diagnose tumor types in many cases and is common to perform with ultrasound guidance. Lymphoma is an example of a cancer type that can often be diagnosed this way.

But hemangiosarcoma often cannot be diagnosed through fine-needle aspiration and cytology alone. This means that tissue biopsy or surgical removal of the tumor often has to be done to know for sure that hemangiosarcoma is involved.

For cutaneous/subcutaneous HSA, excision biopsy where full removal of the tumor is attempted is the most common approach. Given that these tumors are usually smaller, this is also the most efficient approach to both diagnose and treat the tumor at the same time.

Unfortunately, this is trickier for visceral HSA. When a cat has symptoms as those listed for visceral HSA, a veterinarian will often advise running bloodwork and x-rays. In these cases, ultrasound is becoming a more common initial assessment to check for signs of fluid and bleeding in the chest or abdomen. In one study, tumor location could be identified with chest or abdominal ultrasound in about 75% of cases.

If signs of tumors are found, fine needle aspiration may be initially attempted if deemed safe and appropriate. But if a diagnosis cannot be determined this way, surgical biopsy may be discussed as long as the kitty patient can be stabilized for such a procedure.

Bloodwork is a common first step for any very ill cat, but is not able to diagnose hemangiosarcoma specifically. Anemia (low red blood cell count) is the most common finding, which is present in about 80% of cats with visceral HSA. Liver or kidney values may be abnormally elevated if those organs are affected, but other lab work findings may be non-specific and hard to interpret without more information.

Treatments for Hemangiosarcoma in Cats

Surgery is the most common treatment approach for hemangiosarcoma in cats. Andrii Medvednikov / Shutterstock.com

Surgery

The initial treatment for hemangiosarcoma is surgical excision of the tumor. This is regardless of location.

In the case of cutaneous or subcutaneous HSA, removal of the entire tumor is usually always attempted.

Unfortunately, hemangiosarcoma is a tumor with a high risk of recurrence. This is especially true if the entire tumor cannot be removed or if adequate margins of normal tissue around the tumor cannot be obtained.

Cutaneous tumors have the best chance of complete surgical removal. One study reported that of 23 cats, 17 had complete removal of their skin tumors, which is nearly 75%.

It is much harder to get full removal with complete surgical margins of subcutaneous tumors and local recurrence at the surgery site is common. The same study mentioned above saw only 1 out of 16 surgical cases in cats where complete tumor removal was possible. Local recurrence of these tumors at the surgical site is estimated to be about 60%.

Visceral hemangiosarcoma often has a very poor outcome because of how difficult it is to diagnose early before it causes severe illness. It also can spread quickly to multiple sites in the body, making it hard for surgery to completely address.

In studies, an estimated 50–70% of cats with visceral HSA are euthanized within one day of presenting at a veterinary hospital with signs of illness.

Of about 25 cats in one study, half went to surgery for visceral HSA. Of that number, tumor removal was attempted in only 8 cats. In the others, the disease was considered too extensive, leading to euthanasia.

Chemotherapy

Chemotherapy is a treatment option that can be pursued following surgery with the goal of slowing down the further spread of the cancer. However, this treatment option is only pursued in a very small number of cats. In one study, only two cats received chemotherapy. In dogs with HSA, survival time is better with chemo, but there is too little data in cats to know.

Of cats treated for visceral HSA, the median survival time was only about 77 days. Survival ranged from only 23 days up to 296 days. In general, visceral HSA in cats usually results in very poor outcomes, and treatment does not result in a cure but is more palliative in nature.

In my own experience, patients with HSA who have a single larger bleeding tumor in the spleen may be the best candidates for palliative surgery where quality of life may be good for a period of time. Because the entire spleen can be removed, the source of significant bleeding can also be removed. This provides resolution of illness for a period of time, though usually only for a couple of months at best.

Prevention of Hemangiosarcoma in Cats

Ultrasound can be a way to detect signs of hemangiosarcoma early, especially in organs like the spleen. Chris Vanderhoof / Cats.com

There is no known way to prevent visceral hemangiosarcoma in cats. However, there are methods of early detection that may lead to a better outcome. Most cats with visceral hemangiosarcoma aren’t diagnosed until they are severely ill.

Biannual health screening with an examination and blood work may pick up early signs of HSA. Bloodwork may show signs of early anemia, prompting further testing. Annual screening with imaging, like x-rays and ultrasounds, can help to pick up organ abnormalities or masses in the abdomen or chest before signs of illness occur.

In one of my own patients, I detected a mass on her spleen during a routine wellness exam. She had shown no signs of illness. Her spleen was removed and she did favorably for several months. Because visceral HSA usually has a much shorter survival time in many cats, early detection may have made the difference in her case. This highlights the importance of routine wellness exams, especially in cats 10 years of age or older.

For cutaneous/subcutaneous HSA, limiting sun exposure is important, especially at peak times of the day. Indoor cats are at much less risk compared to outdoor cats, but some risk still exists for our indoor kitties. This is especially true for cats with light pigmented skin/coats and short haired breeds.

Sunscreen can be used, but it’s best to stick with brands designed for cats. Avoid any products with zinc or salicylates that a cat may ingest through grooming.