Treatment of Cancer in Pets

Cancer can be treated in both people and animals

As in people, many tumours are readily treated and several types can be cured. Even some malignant tumours can be cured if caught early.

Early diagnosis and appropriate treatment are the keys towards a successful outcome. Your pet cannot choose what cancer they will get but you can choose the best cause of action.

Some tumours, whilst not curable, may be kept under control for a good period of time allowing the pet to enjoy good quality of life. Unfortunately, some tumours are too aggressive or advanced for any treatment and then euthanasia may be the kindest option.

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As in people, many tumours are readily treated and many can be cured. Early diagnosis and appropriate treatment are the keys towards a successful outcome. Your pet cannot choose what cancer they will get but you can choose the best cause of action.

If you have any further questions about any aspect of cancer in your pet, you should speak to your vet who will be able to discuss this with you more fully.

If you are concerned about the health of your pet you should contact your vet.

Many tumours, including a number that are malignant, can be cured if caught early. Some tumours, whilst not curable, may be kept under control for a good period of time allowing the pet to enjoy a normal, happy quality of life. Unfortunately, some tumours are too advanced for any treatment and then euthanasia may be the kindest option.

The most important part of treatment is early diagnosis. A wait-and-see approach is best avoided as the majority of tumours do not disappear and indeed, they will continue to grow.

There are many different types of tumours and the treatment for each can differ. To ensure the most effective treatment is given and to get an idea of the likely outcome a biopsy will be needed. This is usually best performed before any attempt is made to remove the tumour. Contrary to popular belief, taking a biopsy does not increase the risk of spread if performed correctly. 

There are many different types of tumours and the treatment for each can differ. To ensure the most effective treatment is given and to get an idea of the likely outcome a biopsy will be needed to get an accurate diagnosis by a pathologist. This is usually best performed before any treatment is begun.

There have been major advances in the treatment of cancer in humans and many new medicines and techniques can be used in pets too.

Surgery remains one of the best ways to treat most tumours and in many cases can be curative. However, surgery must be bold; any tumour cells left behind will cause the tumour to grow back. 

Radiotherapy is another important means to treating cancer in pets; many tumours will respond to radiotherapy. In particular, some of those in the mouth, nose, skin and brain. Certain tumours can be cured, some are slowed but, unfortunately, some do not respond at all. 

Anti-cancer drug therapy can be used against some tumours (especially leukaemias and those of the lymph glands). This is a form of chemotherapy but the doses used in animals are carefully calculated to avoid unpleasant side effects. 

Referral to a specialist centre for treatment may be necessary for more advanced treatments. (See What is a second opinion and what is a referral? Below)

Tumours are more common in older pets but with due care there is often no reason why they should not be treated. If it were not for the tumour, many pets are otherwise healthy individuals. Surgery, and to a lesser extent radiotherapy, can often be curative. Drug treatment and radiotherapy can often achieve good periods of remission with a return to an excellent quality of life. For a 10-year-old dog, an extra year is ten per cent of its life. Whether to treat a pet with cancer is an important decision and needs to take into account many factors including quality of life for the pet, with, and without treatment.

It is often said of people that you are as old as you feel – this is equally true of animals. If an individual is healthy and active, their age should not be a barrier to treatment. As long as any concurrent disease is considered in the treatment plan, there is no reason that treatment cannot be pursued. It is your right and responsibility, as the pet owner, to make an informed decision.

Yes, cancer is treatable. Cancer treatment may include surgery, radiation therapy, chemotherapy, hormone therapy, and/or biological therapy.  The 3 main types of therapy used in veterinary oncology are surgery, radiation therapy, chemotherapy or a combination of these methods.

Veterinary surgeons may use one method or a combination of methods, depending on the type and location of the cancer, whether the disease has spread, the patient's age and general health, and other factors. Because treatment for cancer can also damage healthy cells and tissues, it often causes some side effects. Some people may worry that the side effects of treatment are worse than the disease. However, owners and veterinary surgeons generally discuss the treatment options, weighing the likely benefits of killing cancer cells and the risks of possible side effects. Veterinary surgeons can suggest ways to reduce or eliminate problems that may occur during and after treatment.

Many owners want to take an active part in making decisions about their pet’s medical care and it is natural to want to learn all you can about your pet’s disease and treatment choices. However, it is often difficult to take in everything that your veterinary surgeon says after the diagnosis is made. It often helps to make a follow-up appointment and to prepare a list of questions before the appointment.

What is the diagnosis?

Is the cancer likely to spread?

Has the cancer spread? If so, where? What is the stage of the disease?

What is the prognosis?

What is the goal of treatment? What are my treatment choices? Which do you recommend? Why?

What are the expected benefits of each kind of treatment?

What are the risks and possible side effects of each treatment? How can side effects be managed?

What can I do to prepare my pet for treatment?

How often will my pet have treatments? How long will each treatment last?

Will I have to change my pet’s normal activities? If so, for how long?

What is the treatment likely to cost? Will my insurance cover the costs?

What new treatments are under study? Would a clinical trial be appropriate for my pet?

Would the treatment options be different if my pet was referred to a specialist surgeon or oncologist?

Your vet will discuss with you the diagnosis and type of cancer as well as the prognosis and management plan. It is up to you to make an informed decision but it is the responsibility of your vet to tell you all the options.

To help remember what you are told, you may wish to take notes or ask whether you may record the conversation. Some people also want to have another family member or friend with them when they talk to the veterinary surgeon - to take part in the discussion, to take notes, or just to listen.

You do not need to ask all your questions at once. You will have other chances to ask the veterinary surgeon or nurse to explain things that are not clear and to ask for more information.

Your veterinary surgeon may refer you to a specialist, or you may ask for a referral. Specialists who treat cancer include surgeons, medical oncologists and radiation oncologists.

The treatment plan depends mainly on the type of cancer and the stage of the disease.

Veterinary surgeons also consider the patient's age and general health. Sometimes the goal of treatment is not to cure the cancer but to maintain as normal a quality of life as possible in your pet for as long as possible. In this case, the goal is to control the disease or to reduce clinical signs associated with the cancer for as long as possible. The treatment plan may change over time.

Before starting treatment, you may want another opinion about your pet’s diagnosis and treatment plan. A second opinion is usually sought when there is doubt about the diagnosis or treatment whereas a referral is usually to seek specialist management of the case (See What is a second opinion and what is a referral?).

Complete remission (CR) is defined as when the tumour can longer be detected. This can be based on physical size or by imaging with radiography or ultrasound. Unfortunately complete remission is not the same as a cure. Generally the smallest mass that can be detected by radiographs is about 0.5 cm, more sophisticated imaging can detect down to 0.25cm but this still represents approximately a million cells.

Partial remission (CR) is defined as a reduction in size by more than 50%. Static or stable disease is defined as change in size (smaller or larger) of less than 25% and progressive disease is defined as increase in size of more than 25%. Using these definitions helps your vet to define the next course of action.

Most treatment plans include surgery, radiation therapy, chemotherapy or a combination of these methods. Some cancer treatments involve hormone therapy or biological therapy. Some cancers respond best to a single type of treatment. Others may respond best to a combination of treatments. Treatments may work in a specific area (local therapy) or throughout the body (systemic therapy).

Very few clinical trials are performed in pets with cancer. Therefore, most of the information available on how well animals do after being diagnosed with cancer comes from studies that follow a series of cases.

Local therapy removes or destroys cancer in just one part of the body. Surgery to remove a tumour is local therapy. Radiation therapy to shrink or destroy a tumour is usually local therapy as well.

Systemic therapy sends drugs or substances through the bloodstream to destroy cancer cells all over the body. It kills or slows the growth of cancer cells that may have spread beyond the original tumour. Chemotherapy, hormone therapy, and biological therapy are usually systemic therapies.

Your veterinary surgeon can discuss the treatment choices and the expected results. You and your veterinary surgeon can work together to decide on a treatment plan that is best for your pet.

Because cancer treatments often damage healthy cells and tissues, side effects are relatively common. Side effects depend mainly on the type and extent of the treatment. Side effects may not be the same for each animal, and they may change from one treatment session to the next. At any stage of cancer, supportive care is available to relieve the side effects of therapy, to control pain and other signs such as nausea.

Surgery is an operation to remove cancer. In most cases, the veterinary surgeon removes the tumour and some tissue around it. Removing nearby tissue may help prevent the tumour from growing back. The veterinary surgeon may also remove some nearby lymph nodes.

The side effects of surgery depend on many factors, including the size and location of the tumour, the type of operation, and the patient's general health. It takes time to heal after surgery. The time needed to recover is different for each type of surgery. It is also different for each patient. Most animals recover much faster from surgery than people.

Most patients are uncomfortable or have some pain after surgery, although this pain can be controlled with medicine. Before surgery, you should discuss the plan for pain relief with the veterinary surgeon or nurse. The veterinary surgeon can adjust the plan if your pet needs more pain relief.

Some owners may worry that having surgery (or even a biopsy) for cancer will spread the disease. This seldom happens. Surgeons use special methods and take many steps to prevent cancer cells from spreading. For example, if they must remove tissue from more than one area, they use different instruments for each one. This approach helps reduce the chance that cancer cells will spread to healthy tissue.

Similarly, some people worry that exposing cancer to air during surgery will cause the disease to spread. This is not true. Air does not make cancer spread.

Radiation therapy (also called radiotherapy) uses high-energy rays to kill cancer cells in a targeted area. Radiation can be given externally by a machine that aims radiation at the tumour area. Radiation treatments are painless. The side effects are usually temporary, and most can be treated or controlled. In animals most side effects from radiotherapy are local and may include hair loss, scaling or itchy skin and/or inflammation of the gums if used in the mouth.

There is no risk of radiation exposure from coming in contact with a patient undergoing external radiation therapy. External radiation does not cause the body to become radioactive. With internal radiation or brachytherapy, an animal may need to stay in the hospital, away from people, for a couple of days while the radiation level is highest.

In cancer treatment, chemotherapy is the use of drugs that kill cancer cells throughout the body. Healthy cells can also be harmed, especially those that divide quickly. The veterinary surgeon may use one drug or a combination of drugs. Most patients receive chemotherapy by mouth or through a vein. Either way, the drugs enter the bloodstream and can affect cancer cells all over the body. Chemotherapy is often given in cycles. Most patients have their treatment at the veterinary practice or at home. Some patients may need to stay in the hospital during chemotherapy.

Anticancer drugs have potential side effects some of which can be serious and potentially life-threatening, however with the doses used in veterinary oncology these are uncommon or mild. The side effects of chemotherapy depend mainly on the drug(s) and the dose(s) the patient receives. Although hair loss is a common side effect of chemotherapy in people it does not occur in most breeds of dogs and cats. Breeds such as poodles, old English sheepdogs, bearded collies and others with continuously growing hair do tend to go bald. Anticancer drugs may also cause temporary fatigue, poor appetite, nausea and vomiting, diarrhoea, and mouth sores. Drugs that prevent or reduce nausea and vomiting can help with some of these side effects.

When drugs damage healthy blood cells, your pet may be prone to infections, to bruise or bleed easily. Normal cells usually recover when chemotherapy is over, so most side effects gradually go away after treatment ends.

Although the side effects of chemotherapy can be distressing, most of them are temporary. Your veterinary surgeon can usually treat or control them.

Having cancer does not always mean having pain. Whether a patient has pain may depend on the type of cancer, the extent of the disease, and the patient's tolerance for pain. Most pain occurs when the cancer grows and presses against bones, organs, or nerves. Pain may also be a side effect of treatment. However, pain can generally be relieved or reduced with prescription medicines recommended by your veterinary surgeon.

Some people with cancer use complementary and alternative medicine (CAM). An approach is generally called complementary medicine when it is used along with a standard treatment(s). An approach is called alternative medicine when it is used instead of standard treatment. However there are no controlled trials in pets that show any benefit from ‘alternative medicine’.

Acupuncture, massage therapy, herbal products, vitamins or special diets, visualization, meditation, and spiritual healing are types of CAM. Many people say that CAM helps them feel better. However, some types of CAM may change the way standard treatment works. These changes could be harmful. Other types of CAM could be harmful even if used alone. Before starting these types of treatment for your pet, you should discuss this with your veterinary surgeon.

Your pet needs enough calories to maintain a good weight. Your pet also needs enough protein to remain strong. Eating well may help your pet feel better and have more energy. Sometimes your pet may not feel like eating. Your pet may be uncomfortable or tired. Your pet may find that foods do not taste as good as they used to. In addition, the side effects of treatment (such as poor appetite, nausea, vomiting, or mouth sores) can be a problem. If your pet is having trouble chewing and swallowing, you may need to add sauces and gravies. Your veterinary surgeon can suggest ways to help your pet to eat well.

Many owners want to know how they can help their pet fight cancer by eating certain foods or taking vitamins or supplements. But, there are no studies that prove that any special diet, food, vitamin, mineral, dietary supplement, herb, or combination of these can slow cancer, cure it, or keep it from coming back. In fact, some of these products can cause other problems by changing how your cancer treatment works. It is best to talk to your veterinary surgeon before putting your pet on a special diet or giving any supplements.

Advances in early detection and treatment mean that many people with cancer are cured. Unfortunately, cancer is often diagnosed relatively late in the course of the disease in pets. This is because the clinical signs are often vague and animals are good at hiding when they are sick.

As veterinary surgeons, we can never be certain that the cancer will not come back once it has been treated. Undetected cancer cells can remain in the body after treatment. Although the cancer seems to be completely removed or destroyed, it can return. We call this a recurrence.

To find out whether the cancer has spread or returned, your veterinary surgeon may do follow-up laboratory, radiographs and other tests. If your pet has a recurrence, you and your veterinary surgeon will discuss new treatment goals and a new treatment plan.

During follow-up exams, your veterinary surgeon will also check for other problems, such as side effects from cancer therapy that can arise long after treatment. Check-ups help ensure that changes in health are noted and treated if needed. Between scheduled visits, you should contact the veterinary surgeon if any health problems occur.

Follow-up care means seeing a veterinary surgeon for regular medical check-ups. Your pet’s follow-up care depends on the type of cancer and type of treatment as well as your pet’s overall health. It is usually different for each patient who has been treated for cancer. In general, patients usually return to the veterinary surgery every x to x weeks/months during the first x months after treatment and then x frequently after that. At these visits, your veterinary surgeon will look for side effects from treatment and check if the cancer has returned (recurred) or spread (metastasized) to another part of the body.

It is important to be able to talk openly with your veterinary surgeon. Both of you need information to manage your pet’s care. Be sure to tell your veterinary surgeon if your pet is having trouble doing everyday activities and talk about new signs to watch for and what to do about them. If you are concerned that the treatment your pet had puts it at a higher risk for having other health problems, be sure to discuss this with your veterinary surgeon as you develop your pet’s follow-up plan.

At each follow-up visit, it is a good idea to mention any health issues your pet is having, such as:

New signs of illness or pain

Physical problems that get in the way of daily life or that bother you, such as tiredness or weight gain or loss

Other health problems your pet may have, such as heart disease, diabetes or arthritis

Things you want to know more about, such as new research or side effects



Just because your pet has certain signs, it doesn't always mean the cancer has come back. Signs can be due to other problems that need to be addressed.

The term "cancer survivor" is used to include anyone who has been diagnosed with cancer, from the time of diagnosis through the rest of his or her life. Family members, friends and other pets are also part of the survivorship experience. While the word may seem strange and you may feel that it does not apply to your pet, the word "survivor" helps many people think about life beyond the cancer for their pets.

While cancer is a major event for all whose pets are diagnosed, it brings with it the chance for growth. As hard as treatment can be, many owners of cancer survivors say that every additional day they had to spend with their pet was worth it. Many say they have drawn from their experience to help other pet owners or to become advocates to improve cancer research, treatment and care.

The end of cancer treatment is often a time to rejoice. You are probably relieved to be finished with the demands of treatment and are ready to put the experience behind you. Yet at the same time, you may feel sad and worried. It's common to be concerned about whether the cancer will come back and what you should do after treatment. When treatment ends, you may expect life to return to the way it was before your pet was diagnosed with cancer. But it can take time to recover. Your pet may have permanent scars or may no longer be able to do some things. People who have gone through cancer treatment describe the first few months as a time of change. It's not so much "getting back to normal" as it is finding out what's normal for your pet now. You can also expect things to keep changing as your pet’s recovers. The new "normal" may include making changes in the way your pet eats and the things they can do. All cancer survivors should have follow-up care. Knowing what to expect after cancer treatment can help you and your family make plans, lifestyle changes, and important decisions.

Some questions you may have after treatment include the following:

Should I tell the veterinary surgeon about symptoms that worry me?

Which veterinary surgeons should I see after treatment?

How often should I see my veterinary surgeon?

What tests do I need?

What can be done to relieve pain, fatigue, or other problems after treatment?

How long will it take for me to recover and feel more like myself?

Is there anything I can or should be doing to keep cancer from coming back? 

A second opinion is usually sought when there is doubt about the diagnosis or treatment whereas a referral is usually to seek specialist management of the case. 

The Royal College of Veterinary Surgeons' guidelines to referrals are:

"Part 2D Referrals and second opinions

34. All veterinary surgeons should recognise when a case is outside their area of competence and be prepared to refer it to a colleague whom they are satisfied is competent to carry out the investigations or treatment involved. They should also be aware that the client has a right to request a referral or second opinion. Care must be taken not to give the impression to the client that the referral is to an 'RCVS recognised specialist' if this is not so. The initial contact should be made by the primary veterinary surgeon, and the client then asked to arrange the appointment.

35. The distinction between a second opinion and a referral should be clearly understood by both veterinary surgeon and client. A second opinion is for confirmation of diagnosis, whereas a referral to a referral practice will be for diagnosis and possible treatment, after which the case will be referred back to the original practice. Neither a second opinion veterinary surgeon nor a referral practice should ever seek to take over the case.

36. The referring veterinary surgeon has a responsibility to ensure that the client is fully aware of the level of expertise of the referral veterinary surgeon, for example as a 'specialist' by experience, a certificate holder, or an 'RCVS recognised specialist'. The referral veterinary surgeon should discuss the case with the client and report back to the primary veterinary surgeon.

37. A full case history and instructions as to the particular reason for referral should be supplied, together with an indication of the client's wishes and responsibility for the fees incurred. Any further information which may be requested should be supplied promptly.

Millicent’s Story

When I was aged seven, I stopped eating, and we all know that things are serious when a Labrador stops eating. Jonathan felt my tummy, and found some lumps that shouldn’t have been there. My local vet thought I had lymphoma and was pretty pessimistic about my chances. Luckily, Jonathan knew another vet who specialised in animal cancer. I was taken to see him, and he prescribed chemotherapy. After quite an unpleasant experience with all the medication, including a three day stay in my local dog hospital with a drip in my leg, here I am!

It was difficult at times for Nina and Jonathan. Halfway through my course of medicine, Nina thought that they should have let me quietly slip away - although I don’t do anything quietly if I can help it. She’s jolly pleased now though, and I get extra cuddles every day. As Jonathan says, the only way to be certain of dying of cancer is not to be treated for cancer!

My local pet doctor tells other dogs about me, and they are offered treatment, rather than a ‘no hope’ diagnosis. So even though I felt rather poorly at times during the couple of months of chemotherapy, I have helped other dogs with the same illness. I am really quite famous around these parts. So, nearly three years on, and I’m still the boss of the house. I always was a stubborn little madam!