Written by A closer look at hemangiosarcoma
Hemangiosarcoma (often shortened to HSA) is a cancer of the cells that line blood vessels. Because blood vessels run through every part of the body, it can start almost anywhere. In dogs it most often starts in the spleen. The heart, the liver, and the skin and the tissue beneath it are the other common sites.
The tumors are made of fragile, blood-filled vessels. They can leak a little, seal over, and leak again, or they can burst and bleed heavily into the belly or into the sac around the heart. That is why this cancer so often seems to come from nowhere: a dog that was fine at breakfast can be too weak to stand by the evening.
It is also a cancer that spreads early. Cornell University’s veterinary college describes it as highly malignant and quick to spread, usually to the lungs and to organs in the belly such as the liver. In many dogs, tiny deposits have already spread by the time the first tumor is found, even when chest X-rays and ultrasound look clear.
This page is honest about a hard subject. For the internal forms, treatment usually buys good time and does not cure. But not every bleeding spleen is cancer, the skin form can behave very differently, and there are real choices to make at every step. Knowing them ahead of time helps.
The three main forms
| Where it starts | How it usually shows up | What is different about it |
|---|---|---|
| Spleen (most common) | Vague tiredness, a swollen belly, or sudden collapse with pale gums after a bleed. Sometimes found by chance during an exam or scan. | The spleen can be removed, which stops the bleeding and gives a firm diagnosis. |
| Heart (usually the right atrium) | Blood collects in the sac around the heart and squeezes it. Dogs become weak, collapse or build up fluid in the belly. | Surgery is rarely possible. Draining the fluid gives fast but temporary relief. |
| Skin and under the skin | A red to purple bump, a “blood blister”, or a patch that looks like a bruise and may bleed. | Tumors confined to the skin can often be treated with surgery alone. Deeper ones act more like the internal forms. |
The forms can overlap. The World Small Animal Veterinary Association (WSAVA) notes that about 10 percent of dogs with a splenic tumor also have a mass in the right atrium of the heart, which is one reason vets often suggest a heart scan before surgery.
Risk factors
- Age. This is mainly a cancer of older dogs. The American College of Veterinary Surgeons (ACVS) says it typically affects dogs aged 8 to 10 years, and it is rare in young dogs.
- Size and breed. Large breeds are affected most. German Shepherds, Golden Retrievers and Labrador Retrievers are named by Cornell, NC State and ACVS. Any breed, including mixed breeds, can be affected.
- Sun exposure, for the skin form only. The Merck Veterinary Manual lists Whippets, Italian Greyhounds, white Boxers and pit bull-type dogs as prone to sun-related skin tumors, which form on thinly haired, pale skin such as the belly and inner thighs. Sunlight is not thought to play a part in the internal forms.
Causes
For most dogs, nobody knows. The breed pattern suggests that inherited factors play a part, and research groups are studying the genetics. Nothing an owner fed, did or missed is known to cause the internal forms. If your dog has been diagnosed, you did not cause this.
Signs of hemangiosarcoma
Many dogs show nothing at all until a tumor bleeds. When there are early signs, they are easy to put down to age:
- Tiring more easily, or less interest in walks and play
- A poorer appetite or slow weight loss
- An “off day” of weakness and pale gums that seems to pass by the next morning (a small bleed that the body has reabsorbed)
- A belly that looks rounder than usual
A larger bleed is hard to miss:
- Sudden weakness or collapse
- Pale or white gums
- Fast or labored breathing and a racing heart
- A swollen, tight belly
- Fainting
Skin tumors look different: a dark red or purple lump, a blood-filled blister, or a bruise-like patch that does not fade and may bleed. Looks and feel cannot tell a harmless lump from a malignant one, so any lump like this needs a vet to sample or remove it.
Emergency or wait?
| What you see | What to do |
|---|---|
| Red: go now. Collapse, pale or white gums, fast or hard breathing, a swollen belly with weakness, fainting. | Go to the nearest open vet or 24-hour emergency hospital straight away. Phone from the car if you can. Do not wait to see whether it passes. |
| Amber: same day or next day. An older dog that had a spell of weakness and recovered, a new red or purple lump that is bleeding, or a belly that has slowly grown rounder. | Call your vet today and describe exactly what happened. A spell that passes can be a small bleed, and the next one may be larger. |
| Green: book a routine visit. A small skin lump that is not growing or bleeding, or an older large-breed dog that is slowing down with no other signs. | Make an appointment in the next week or two and ask for a full exam. |
What happens at the vet
If your dog arrives collapsed, the team treats first and investigates second. This is the usual order of events:
- Stabilizing. Staff check the gums, heart rate, breathing and blood pressure, place an IV line and start fluids. A dog that has lost a lot of blood may need a blood or plasma transfusion.
- A quick scan. A brief ultrasound of the belly and chest shows whether there is free fluid. A needle sample of the fluid confirms whether it is blood.
- Blood tests. These measure how anemic your dog is and how well the blood is clotting. WSAVA notes that low red cells, low protein, low platelets and abnormal clotting tests are all common.
- Imaging to look for spread. A full abdominal ultrasound looks at the spleen and liver. Chest X-rays or a CT scan look for spread to the lungs. An echocardiogram (heart ultrasound) checks the right atrium, where a tumor is hard to see on X-rays.
- A frank conversation. With the results in hand, the vet will tell you what they can and cannot know before surgery, what each option costs, and what it is likely to achieve.
- If the heart is involved. When blood around the heart is squeezing it, the vet drains it with a needle and catheter through the chest wall. The Merck Veterinary Manual describes this as a relatively easy procedure in dogs with rare serious complications. Draining relieves the pressure on the heart, though the fluid can return.
One point surprises many owners: the scans cannot give the final answer. Needle samples of these tumors are often unhelpful because they are mostly blood, and puncturing them can cause bleeding. A firm diagnosis needs the tissue itself, examined by a pathologist. So the decision about surgery often has to be made without knowing for certain whether the mass is cancer.
That uncertainty cuts both ways. According to ACVS, benign masses such as hematomas and nodular hyperplasia account for 20 to 41 percent of splenic lesions, and up to two-thirds of splenic masses are cancerous, most often hemangiosarcoma. Our glossary entry on spleen tumors in dogs explains the other possibilities.
Treatment
Surgery
For a tumor in the spleen, the operation is a splenectomy: the whole spleen is removed. It stops the bleeding, removes the risk of the next bleed from that tumor, and provides the tissue for diagnosis. If the mass has already ruptured, ACVS advises surgery as soon as the dog is stable enough.
Most dogs stay in the hospital for 24 to 48 hours afterward so the team can watch for further bleeding and for irregular heart rhythms, which are a known complication of this surgery and usually settle within a day or two. At home, expect two weeks of short leash walks only, and a cone or recovery shirt to protect a long incision.
Skin tumors are removed with a wide margin of normal tissue around them. Heart tumors can rarely be removed.
Chemotherapy
Because the internal forms have usually spread at a microscopic level, chemotherapy is normally recommended after surgery. The standard drug is given through an IV at the clinic every two to three weeks for four to six visits. Some dogs are given a low-dose oral plan at home instead of, or after, the IV course.
Chemotherapy in dogs is not the ordeal many people picture. NC State’s veterinary hospital describes side effects as infrequent and usually mild, with hair loss rare outside a few breeds such as Poodles. The goal is more good days, not a cure at any price.
Radiation
Radiation has a smaller role. It may be offered when a tumor cannot be removed, or for skin tumors that could not be removed completely.
Comfort care only
Some families choose not to operate, because of the dog’s age, other illnesses, signs of spread, or cost. That is a reasonable choice. Your vet can explain what to expect, how to keep your dog comfortable, and how to recognize when another bleed means it is time to say goodbye. Choosing euthanasia for a dog that is bleeding internally from a cancer that cannot be cured is a kind decision, not a failure.
Supplements and trials
You will read about Yunnan Baiyao (a Chinese herbal product) and turkey tail mushroom extracts. Sources disagree: some hospitals mention them as add-ons, while WSAVA’s fact sheet says current data does not support either for splenic hemangiosarcoma. Ask your vet before giving anything. If you want to try something new, ask a veterinary oncologist about clinical trials.
Outlook
These figures come from the sources listed at the end of this page. They describe groups of dogs, and your own dog may do better or worse.
| Situation | What the sources report |
|---|---|
| Splenic mass that turns out to be benign | Effectively cured by surgery (ACVS). |
| Splenic hemangiosarcoma, surgery alone | An average of about two months (Cornell); about two to three months or less (ACVS). |
| Splenic hemangiosarcoma, surgery plus chemotherapy | A median of four to six months (Cornell); ACVS says chemotherapy may extend survival to six to eight months. |
| By stage, with surgery and chemotherapy (WSAVA projected medians) | Unruptured splenic mass: 6 to 12 months. Ruptured: 2 to 6 months. Spread to distant organs: 1 to 2 months. |
| One year after diagnosis of splenic hemangiosarcoma | Fewer than 10 percent of dogs are alive (Cornell, ACVS). |
| Heart (right atrium) | Similar to the splenic form (Cornell); poor to grave (Merck Veterinary Manual). |
| Skin only | Variable and often better; may need surgery alone. Tumors that reach into muscle can be as aggressive as the internal forms (Cornell). |
A “median” means half of dogs lived longer than that figure and half lived less. What the numbers do not show is that, between bleeds, most dogs feel well. Many owners describe the weeks or months after surgery as normal, happy time.
How much treatment costs
Costs vary widely by city, hospital and how sick the dog is on arrival. As one published example, NC State Veterinary Hospital, a university teaching hospital, lists these estimates on its hemangiosarcoma page (viewed November 2026). They do not include supportive care or hospital stays.
| Treatment | NC State’s published estimate |
|---|---|
| Surgery | $6,000 to $8,000, more for some locations |
| IV chemotherapy | $600 to $800 per treatment, depending on body weight, for 4 to 6 treatments |
| Palliative radiation | $2,000 to $6,000; a CT scan may be needed first |
| Full-course radiation for skin tumors not fully removed | $10,000 to $12,000; a CT scan may be needed first |
A specialty teaching hospital is not the same as your local clinic, and prices elsewhere may be lower or higher. Always ask for a written estimate with a low and a high figure before you agree to treatment, and ask what the emergency exam alone will cost. Our guide to what a vet visit costs explains how exam and emergency fees work, and our glossary has a plain-English look at whether pet insurance is worth it. Insurance has to be in place before a problem appears to cover it.
Prevention and early detection
There is no proven way to prevent the internal forms and, so far, no reliable screening blood test, although researchers are working on several. What you can do:
- Keep up regular check-ups for older dogs. A vet can sometimes feel an enlarged spleen, and some splenic masses are found by chance on a scan done for another reason.
- Take “off days” seriously in an older large-breed dog, especially weakness with pale gums that passes within a day.
- Protect pale, thin-coated dogs from strong sun. Shade, and keeping sunbathers indoors in the middle of the day, may reduce new skin tumors. This matters in sunny places like Texas.
- Have new lumps checked, particularly red, purple or bruise-like ones.
- Know where you would go at night. Save your vet’s number and your nearest emergency hospital in your phone. In Houston, you can find clinics in our Houston vet directory.
Questions to ask your vet
- Is there any sign of spread on the chest images, the liver or the heart?
- How likely is it that this mass is benign, given what you see?
- What is the estimate for surgery and the hospital stay, low and high?
- Will my dog need a transfusion, and is blood available here?
- When will the pathology result come back, and who will call me?
- If it is hemangiosarcoma, can you refer us to an oncologist, and are there clinical trials nearby?
- If we choose comfort care, what should I watch for, and what do I do if there is another bleed at night?
Living with the diagnosis
If the result is hemangiosarcoma, the weeks ahead are about good days. A few things help:
- Learn to check gum color. Healthy gums are salmon pink. Look at them when your dog is well so you know what normal is. Pale gums with weakness mean a bleed.
- Make a plan for the next bleed now, while you are calm: which hospital, how far you want to go with treatment, and who in the family decides.
- Keep life normal. Unless your vet says otherwise, gentle walks, favorite foods and routines are good for dogs who feel well.
- Keep a simple diary of good and bad days. When bad days start to outnumber good ones, it is time to talk to your vet about quality of life.
Your vet is the person to ask about your own dog, and a second opinion from an oncologist is always reasonable.