Cancer in dogs: treatment, prognosis and the hardest choices

Reading time: about 20 min

A cancer diagnosis can come as a complete surprise. One moment you have a dog whose daily life seems normal, and the next you are faced with questions you have never had to answer: can my dog ​​be cured, how much more time should be given to him for treatment, and what will his life be like during that treatment? These are not three consecutive stages where quality of life is only considered when other options have been exhausted. All three questions should be on the table from the moment of diagnosis.

Treatment that gives a dog more days to live may not necessarily give them more good days to live. However, active treatment, such as surgery, chemotherapy, or radiation, can improve both well-being and prolong life. There is no one right answer for all dogs. It is important to understand what the disease is, what options are available, and what they mean for that particular dog.

Before comparing treatment options, it’s worth asking yourself two simple but uncomfortably big questions: What do I want to achieve for my dog, and what consequences am I willing to deal with if the treatment doesn’t go as planned? Is the goal to try to cure the disease, prolong life, or focus primarily on making the dog as well as possible? These goals may overlap, but no treatment method is automatically the right choice just because it is technically possible to do so.

Before making a decision, it is also worth asking your veterinarian about the risks of the treatment: which side effects are common, which are rare but serious, whether the possible damage is reversible, how much help the dog may need at home, and what to do if the treatment does not give the expected result. The veterinarian can provide a medical assessment and explain the treatment options, but the owner has the right to decide whether the proposed treatment is suitable for the daily life of their dog and family. And one more important thing: starting treatment does not oblige you to finish it at all costs. If the dog’s well-being turns out to be worse than expected, the treatment plan can be reviewed again with the veterinarian.

Eight types of cancer: what is worth knowing?

There are many different types of cancer in dogs, and their course, treatment options, and prognosis can vary greatly. We have selected eight examples here to help illustrate how the biology of the disease and the treatment decisions can vary. This is not a ranking of the most common or most serious cancers, and the absence of a cancer from the list does not mean that another cancer is less important.

Cancer type	Typical treatment directions	Median/note described in studies
Lymphoma	Chemotherapy, such as CHOP; sometimes steroid therapy	Prednisone alone ~1–2 months; CHOP ~12 months
Osteosarcoma	Amputation or other local treatment; chemotherapy; pain management	Amputation ~4 months; with chemotherapy ~10–12 months
Splenic hemangiosarcoma	Spleen removal; chemotherapy; palliative care	Surgery ~1.5–3 months; with chemotherapy ~3–6 months
Mast cell tumor	Surgery, radiation therapy, systemic therapy if necessary	One general median is not appropriate
Breast cancer	Surgery; additional treatment in selected cases	Depends on the type, stage, and spread of the tumor
Soft tissue sarcoma	Surgery; radiation or adjuvant therapy if necessary	One general median is not appropriate
Malignant melanoma of the oral cavity	Surgery, radiation therapy, other treatments in selected cases	~5–17 months in treatment groups that included surgery
Urothelial carcinoma	NSAIDs, chemotherapy, radiation therapy, and other interventions	NSAID alone ~6 months; with chemotherapy ~12 months

Median survival is the time until which half of the dogs in a given study group have survived and half have not. It is not a prediction of how long an individual dog will live. Results depend on factors such as the type of cancer, the stage of the disease, the biology of the tumor, and the treatment used. They may not apply to dogs that already have metastases at the time of diagnosis, and the difference in medians between two treatment groups does not automatically indicate how many additional months the treatment will give a particular dog.

What do these types of cancer actually mean?

The following symptoms do not automatically mean that your dog has cancer. There are many other diseases that can cause the same symptoms. The goal is to help you spot changes and understand why your doctor may recommend further testing rather than making a diagnosis at home.

Lymphoma

Lymphoma is a cancer of the lymphocytes that can affect the lymph nodes, spleen, liver, digestive tract or other organs. Common aggressive forms can develop quickly, but there are also lymphomas that progress more slowly. One of the most common first signs is enlarged lymph nodes, for example under the chin, on the neck, in front of the shoulders or behind the knees. They may be painless and the dog may otherwise seem perfectly healthy. Later, fatigue, weight loss and loss of appetite may occur. Because lymphoma is often a systemic disease, systemic treatment, such as chemotherapy, is usually used; removing one lymph node does not usually solve the whole problem. However, lymph nodes can also become enlarged due to infections and inflammation, so the cause always needs to be diagnosed.

Osteosarcoma, or bone cancer

Osteosarcoma is an aggressive bone tumor that occurs more often in large and giant breed dogs. A tumor located in a limb can cause severe pain, weaken the bones, and increase the risk of fractures due to the disease. The owner often notices persistent or worsening lameness, sometimes also swelling. The disease can spread early, especially to the lungs, which is why the possibility of micrometastases is often discussed at the time of diagnosis. Amputation can remove the painful tumor and the risk of fractures, but is not suitable for every dog, and the decision depends on, among other things, an assessment of the remaining limbs, spine, and general condition. Alternatives may include limb-sparing therapy, stereotactic or palliative radiation therapy, and pain management. Persistent lameness can also be caused by injuries, joint diseases, and infections, so lameness does not automatically equate to bone cancer.

Splenic hemangiosarcoma

Hemangiosarcoma is an aggressive cancer of the blood vessels, and one of the common sites is the spleen. The risk of bleeding is particularly dangerous: the dog may appear to be in good health for a while, but if the tumor starts to bleed, the dog may suddenly become unwell. Signs include weakness, pale gums, abdominal distension or collapse, and such sudden symptoms require immediate veterinary attention. Removal of the spleen can stop the bleeding and allow tissue examination; chemotherapy is often considered in cases of confirmed hemangiosarcoma. At the same time, a mass found in the spleen does not automatically mean cancer, as benign hematomas and other changes may also occur, which may not be clearly differentiated before surgery and histology.

Mast cell tumor

Mast cell tumors are among the most common malignant skin tumors in dogs, but their behavior varies greatly. Some grow slowly and are well controlled with appropriate surgery, while others can be aggressive and spread. A lump in or under the skin may resemble a completely normal fatty tumor; sometimes it changes in size, becomes red, or itchy. Mast cells can release histamine and other substances, which is why some dogs may also experience gastrointestinal symptoms. The choice of treatment is primarily influenced by the histological grade of the tumor, its location, the margins of removal, and possible spread. Not every lump on the skin is cancer, but they cannot always be distinguished by appearance alone.

Breast cancer

Mammary gland tumors can be benign or malignant, and the same dog may have several tumors with different behaviors. The owner may notice a small hard nodule or a larger tumor; some grow slowly, others quickly, and sometimes ulcerate. The prognosis depends on the type of tumor, its size, tissue grade, invasion, and spread. Surgery is often the main treatment option, but the decision depends on the assessment of the specific tumor and the dog’s general condition. Inflammatory and hormonal conditions can also cause changes in the mammary glands, but it is always worth showing a new tumor to a veterinarian.

Soft tissue sarcoma

Soft tissue sarcoma is a general term for several tumors that can arise in the connective tissue, around the muscles, or in the subcutaneous tissue. Often, the owner notices a slow-growing and initially painless mass. However, some tumors can grow faster, attach to surrounding tissues, or begin to interfere with movement. These tumors can extend microscopically further than they appear from the outside, which is why adequate removal is important when planning surgery. Higher-grade tumors have a higher risk of spreading. However, the lump under the skin could also be a lipoma, cyst, or other benign mass.

Malignant melanoma of the oral cavity

Oral malignant melanoma is often an aggressive tumor that can damage oral tissues and spread to the lymph nodes and lungs. Possible signs include bad breath, bleeding gums, difficulty eating, increased salivation, or a visible mass. Not all melanomas are dark, so histology and immunohistochemistry may be required for diagnosis. Local treatment may involve extensive surgery, such as removing part of the jaw, or radiation therapy; systemic treatment options depend on the stage and situation. In addition to tumor control, the treatment decision should also consider the impact on eating, pain, and daily life. Similar signs may be caused by dental disease, inflammation, and other oral tumors.

Urothelial carcinoma of the urinary bladder

Urothelial carcinoma can develop in the bladder, urethra, or other parts of the urinary tract. The disease can grow into surrounding tissue, spread to the lymph nodes, or lungs, and cause obstruction to urine flow. Symptoms may include frequent urination, straining, blood in the urine, or very little urine, and often resemble a cystitis. Not all bladder tumors can be removed surgically; treatment includes nonsteroidal anti-inflammatory drugs, chemotherapy, radiation therapy, and, if necessary, procedures to maintain urine flow. If your dog is straining but no urine is coming out, this is an emergency.

What does it mean when cancer has metastasized?

Metastasis means that cancer cells have spread from the original tumor to other parts of the body and formed new cancer cells there. This does not automatically mean that the cancer has spread “throughout the body.” Some dogs may have a single visible metastasis in the lung or liver, while others may have spread to multiple organs and there may be many metastases.

The impact of the disease is also not solely dependent on the number of metastases. A single metastase can cause serious problems due to its location, while several small metastases may not initially cause noticeable symptoms. The presence of metastases can change both the prognosis and the treatment options, as in the case of distant metastases, removal of the original tumor may no longer be sufficient to control the disease. However, this does not automatically mean that treatment is not possible or that it would not be beneficial for the dog.

Therefore, the word “metastasis” alone cannot tell you how much time your dog has left or what treatment would be best for him. It is important to know what type of cancer it is, where and how far it has spread, what the dog’s general condition is, and how the disease is affecting his well-being.

Bemmu and nineteen weeks of chemotherapy

When Bemmu was diagnosed with lymphoma, I was also faced with the question of what to do next. Should I choose chemotherapy? What would it give him? How would he tolerate it? And what if the treatment turned out to be much more difficult than we initially thought? Bemmu underwent nineteen weeks of chemotherapy. Our regimen consisted of three consecutive weeks of treatment with different drugs, followed by a week off.

Bemmu tolerated the treatment exceptionally well. This does not mean that chemotherapy is easy for all dogs or that there is no reason to fear side effects. It just means that our experience was like that. And this is where an important difference comes into play: studies give us knowledge about groups of dogs, but in real life we ​​also have to look at the specific dog in front of us.

Before starting treatment, my oncologist told me about a rare but very serious potential complication. One of the drugs used was a strong tissue destroyer: if it had leaked into the surrounding tissues through the vein, the damage could have been so severe that, in the worst case scenario, amputation of the limb would have been a possibility. It wasn’t a likely outcome, but it was a potential risk that I had the right to know about before treatment. For me, it was an important boundary.

I knew that if Bemmu had suffered such severe damage that amputation was the only option, I would not have wanted to put him through it and would have considered euthanasia. That was my personal decision and my assessment of the burden I was willing to take on for Bemmu. That doesn’t mean that amputation would be the wrong choice for another dog. That’s why we need to talk about rare serious side effects, not just how often vomiting or diarrhea occurs. Sometimes the treatment decision is not just determined by the likelihood of a side effect, but also by what we do if that side effect does occur.

Starting treatment does not mean you have to finish it.

I had also considered another option for myself. What if Bemmu had vomited and felt unwell for five days after each chemotherapy treatment? Should I have continued just because the treatment regimen called for several more weeks? My answer was no. This does not mean that the treatment should be stopped at the first side effect. Nausea and vomiting can often be alleviated with medication, and in some cases the dosage can be changed, the treatment intervals can be extended, or a different regimen can be chosen. But if the dog’s daily well-being becomes too bad compared to the potential benefit of the treatment, it is worth reconsidering the decision. Starting treatment does not oblige you to finish it at all costs, and the dog’s well-being does not become less important just because we have already started the treatment journey.

Is treatment even possible for the family?

When Bemmu was undergoing chemotherapy, I went to the clinic with her every Thursday. One treatment session took about two to three hours of my workday, and that was for nineteen weeks. I was able to do it. But what if my employer hadn’t made it possible? Or if I hadn’t had the financial means to pay for the treatment? Just because a treatment option is available on paper doesn’t mean it’s feasible for every family in real life.

Before starting chemotherapy, the veterinarian asked me very directly whether I was pregnant or planning to become pregnant. This question was not random. With cytotoxic drugs, one must consider the potential exposure to both the drugs themselves and their residues. Depending on the drug used, drug residues may be present in the dog’s urine, feces, vomit, and other body fluids, including saliva, for some time. Safety instructions vary depending on the drug and the route of administration, so they should be discussed specifically with the treating physician before starting treatment.

Pregnant women, those planning to become pregnant, and those breastfeeding should not handle cytotoxic drugs and are advised to avoid contact with post-treatment secretions. Families with young children or immunocompromised individuals also need to take extra precautions. This does not automatically mean that a dog in such a household cannot receive chemotherapy, but some care tasks may need to be performed by another person or the treatment plan may need to be adjusted.

And now imagine that the dog owner has a seriously ill mother at home, whom he also cares for. Or small children. Or a job that requires several hours of absence each week. It is very easy for an outsider to ask, “But why didn’t you try chemotherapy?” They may not know that the decision was not driven by a desire to help their dog, but by the fact that the treatment could not be arranged safely or practically. The same goes for money. We may want the best possible treatment for our dog, but that doesn’t mean we can afford to pay for it.

These are real limitations. They cannot be made non-existent by someone else saying what they would have done. Therefore, we should not condemn another dog owner’s decision without knowing what options, risks and responsibilities they actually chose between. In Bemmu’s case, I was able to choose chemotherapy. Someone else may make a different decision with the same diagnosis. That in itself does not say anything about which of us loves our dog more.

How much care can actually be provided?

Treatment decisions are often made based on what the dog can physically tolerate, but much less often on what the owner can actually do. When a dog requires 24/7 supervision, frequent medication, assistance with movement, or multiple walks during the night, it inevitably impacts the entire family. This does not mean that the dog is a burden. It simply means that there are real physical and mental limits to caring for it.

I have felt this very clearly with Faddu’s heart disease. When a dog needs to be taken outside three times a night for weeks on end, the question eventually arises as to how long it is possible to go without sleep, go to work and take good care of the dog at the same time. This is not an example of cancer treatment, but the principle is the same: even the most loving owner cannot function indefinitely without sleep and recovery.

I also recall a client’s experience where a dog’s medication caused severe thirst and increased urination. Nighttime walks became so exhausting that the owner eventually took the water bowl away for the night. This is not a recommended solution, and restricting water can be dangerous in cases of increased thirst caused by medication. But this example illustrates what can happen when a treatment plan does not take into account the owner’s actual capabilities. In such a situation, the medication, dosage, possible alternatives, and how to better control symptoms should be reviewed with a veterinarian. An effective treatment plan must also be feasible outside of the clinic.

Is there a place for an integrative approach alongside cancer treatment?

Yes, but it is especially important to distinguish between what we know and what is still being studied. An integrative approach does not have to mean abandoning conventional cancer treatment. It can aim to support appetite, digestion, muscle mass, general well-being and recovery. At the same time, we should not make the leap from a mechanism or a small pilot study to claiming that a food or supplement cures cancer.

A good example is the common turkey tail, or Trametes versicolor. Brown and Reetz studied just 15 dogs with splenic hemangiosarcoma in 2012 and found encouraging results with a specific polysaccharopeptide preparation. This was an interesting signal, not definitive proof. In a prospective study of 101 dogs published in 2022, adding the same type of PSP preparation to doxorubicin did not improve survival, and PSP alone was not superior to standard therapy. Nor can it be concluded from these studies that regular mushroom powder or any “turkey tail” product on the market will work the same way.

There is also some interesting data on omega-3 fatty acids. In a 2000 randomized trial, dogs with lymphoma were given a diet containing both fish oil and arginine, and certain measures were associated with longer disease-free periods and survival. Since the intervention was not solely fish oil, the full potential benefit cannot be attributed to EPA and DHA alone. This is a good example of why “a study shows benefit” does not automatically mean that one ingredient alone will produce the same result.

There are biologically interesting results for curcumin and sulforaphane, but clinical evidence in dogs is limited. For curcumin, most of the stronger anticancer signal has come from cell culture and early studies; a small pilot study of liposomal curcumin in dogs failed to provide evidence to support a survival benefit. For sulforaphane, a prospective study of seven dogs with lymphoma has shown changes in the proteome of tumor cells, but no clinical tumor response has been observed. This does not make these agents useless, but it does put them in the right category: an interesting mechanism and line of research, not a proven cancer treatment.

The value of an integrative approach does not depend solely on whether a supplement can be labeled “anti-cancer.” If a dog eats better, maintains muscle mass, copes better with nausea, or feels better overall, it may have real value. The lack of scientific evidence does not invalidate an owner’s observation, but neither should a single experience be used to make a universal treatment claim. High-dose extracts and supplements should be discussed with a veterinarian during cancer treatment, as potential interactions depend on the specific formulation and regimen.

Does sugar feed cancer?

This is a question that often arises after a cancer diagnosis. Many cancer cells actively use glucose, and this leads to a simple conclusion: if we exclude carbohydrates from the diet, the tumor will starve. However, the body does not work so straightforwardly. Normal cells also need glucose, and the body can produce it itself if necessary.

There is currently insufficient clinical evidence in dogs to recommend a low-carb or ketogenic diet for all animals diagnosed with cancer. Ketogenic diets are being investigated for potential uses, but direct clinical evidence of cancer treatment outcomes in veterinary medicine is still lacking. The more practical question is often whether the dog is eating enough, getting the nutrients it needs, and maintaining weight and muscle mass.

Weight loss associated with cancer does not always mean that the dog is simply not eating enough. The disease can alter metabolism and lead to a loss of muscle mass. Therefore, nutrition should not become another battle where the owner tries to avoid certain ingredients at all costs, but the dog ends up not getting enough energy. If the dog is experiencing nausea, poor appetite or weight loss, these issues should be addressed first before adding additional restrictions to the diet.

If the topic is an older dog’s body weight, muscle mass, and appetite, read more: Senior dog food or what should be changed in an older dog’s bowl?

When does treatment become too burdensome for a dog?

There is no one-size-fits-all answer to this question. Some dogs tolerate intensive treatment well, while for others, relatively small changes in their daily well-being can be a major burden. It is important to look at the big picture: is the dog eating, is he able to rest, is the pain under control, is he able to move, is he still interested in his surroundings, and is the treatment helping him to do these things or is it increasingly hindering him.

One bad day does not necessarily mean that treatment should be stopped. However, you do not have to wait until all days are bad either. There is an important difference between diagnosis and actual quality of life. A diagnosis gives us important information about the disease, but it does not describe the entire life of a dog.

Read more: A diagnosis doesn’t make life uncertain. It makes uncertainty visible.

Latest choices

I have promised my dogs that I will not prolong their suffering just because I am not ready to give them up. It is a promise I have had to keep with two dogs, and I know how difficult the decision is. Euthanasia does not become easy just because you understand with your mind why it may be necessary, nor because you have had to do it before.

Sometimes the hardest part is the time between making a decision and saying goodbye. You look at your dog and think: is now the right time, is there anything else I can do, could tomorrow be a better day? But sometimes you have to ask yourself the opposite question: what if tomorrow is much worse? For example, in the case of bone cancer, uncontrolled pain or the risk of a fracture due to the disease may mean that waiting is no longer in the dog’s best interest.

However, a cancer diagnosis does not mean that euthanasia is the only or right choice. Some dogs can be cured, some can have their disease slowed down, and in some cases, pain and other symptoms can be alleviated so that the dog can have many more good days. And sometimes there comes a point when even the best possible supportive care can no longer provide an acceptable quality of life.

The owner should not be left alone in this decision. The veterinarian can help assess the pain, the course of the disease, possible complications and what kind of relief can still be offered. But in the end, you know your dog’s daily life best. You see the small changes that may not be apparent in the clinic, you know what activities have always brought him joy and when nothing is quite the same. And you have to live with this decision.

We may never know for sure if we did everything right. Should we have tried another treatment or stopped some treatment earlier? Perhaps we don’t need to look for a decision that leaves no doubt. What may be more important is that we have tried to understand our dog’s illness, listened to the recommendations of veterinarians, considered different options, and in doing so, looked at our dog, not just at his diagnosis, test results, or prognosis.

And here’s something else to keep in mind. Other people may have very strong opinions about your dog’s treatment. Some will say you should definitely try something else, others will think you should have stopped earlier. But they may not know what options you’ve actually considered, what your dog has been through, or what your financial, time, health, and family capabilities are to care for him. And they don’t have to live your daily life.

I have made certain choices with my dogs. This does not mean that every other owner should do the same. One person may decide to try another treatment option, another may come to the conclusion with their veterinarian that further treatment would no longer be in their dog’s best interests. Neither decision can be judged solely by whether treatment was continued or discontinued. Therefore, it is worth listening to the recommendations of veterinarians, asking for a second opinion if necessary, and considering your options, but other people’s opinions should not become more important than the actual well-being of your dog.

Because in the end, we get back to the question we started with: what do we want to achieve for our dog? For me, the most important thing is not how many days I get to spend with my dog. What’s more important is what those days are like for him.

Sources

• AAHA. 2026 AAHA Oncology Guidelines for Dogs and Cats. J Am Anim Hosp Assoc. 2026;62(1):1–37. PMID 41448590; DOI 10.5326/JAAHA-MS-7549. Read source
• AAHA. Section 1: Overview of Common Cancers. Table 1.1: Common Cancers of Dogs. Read source
• Polton G et al. Osteosarcoma of the appendicular skeleton in dogs: consensus and guidelines. 2025. PMID 41059462. Read source
• Polton G et al. Melanoma of the dog and cat: consensus and guidelines. 2024. PMID 38645640. Read source
• Smith AN et al. ACVIM small animal consensus statement on safe use of cytotoxic chemotherapeutics in veterinary practice. J Vet Intern Med. 2018;32(3):904–913. DOI 10.1111/jvim.15077. Read source
• NC State Veterinary Hospital. Medical Oncology: Chemotherapy Fact Sheet. Read source
• Brown DC, Reetz J. Single agent polysaccharopeptide delays metastases and improves survival in naturally occurring hemangiosarcoma. Evid Based Complement Alternat Med. 2012;2012:384301. PMID 22988473. Read source
• Gedney A et al. Evaluation of the anti-tumor activity of Coriolus versicolor polysaccharopeptide alone or in combination with doxorubicin for canine splenic hemangiosarcoma. Vet Comp Oncol. 2022;20(3):688–696. PMID 35442554. Read source
• Ogilvie GK et al. Effect of fish oil, arginine, and doxorubicin chemotherapy on remission and survival time for dogs with lymphoma. Cancer. 2000;88(8):1916–1928. PMID 10760770. Read source
• Withers SS et al. In vitro and in vivo activity of liposome-encapsulated curcumin for naturally occurring canine cancers. Vet Comp Oncol. 2018;16(4):571–579. PMID 30088848. Read source
• Parachini-Winter C et al. Prospective evaluation of the lymph node proteome in dogs with multicentric lymphoma supplemented with sulforaphane. J Vet Intern Med. 2020;34(5):2036–2047. PMID 32926463. Read source
• Vendramini THA et al. Ketogenic diets: A systematic review of current scientific evidence and possible applicability in dogs and cats. J Anim Physiol Anim Nutr. 2024;108(2):541–556. PMID 38091342. Read source
• Amaral et al. (2025). Connection between nutrition and oncology in dogs and cats: perspectives, evidence, and implications — a comprehensive review. Frontiers in Veterinary Science 11:1490290. PMID 40046187. Original article; fix published 2026, PMID 42558890. Read source

---

---