Lymphoma is a cancer of white blood cells (lymphocytes) that arises outside the bone marrow. Cancers of white blood cells (and other cells) that originate within bone marrow are termed leukemias. Unfortunately, lymphoma in dogs is not a curable disease, but with effective treatment, many dogs can enjoy a normal quality of life for some time following diagnosis.
Middle aged and older dogs are typically more likely to develop lymphoma, with Basset Hounds, Bull Mastiffs, Bull Terriers, Scottish Terriers and Saint Bernards being predisposed.
In this article, we discuss the common symptoms of lymphoma in dogs, the most effective course of treatment and average survival rates.
What is lymphoma?
Lymphocytes normally travel all around the body and lymphoma (a cancer affecting lymphocytes) can arise anywhere in the body. It is usually therefore a widespread disease process, which affects how we treat it.
Different types of lymphoma in dogs
In dogs, lymphoma is usually classified in two ways: firstly by something called anatomic distribution (whereabouts in the body the tumour arises) and secondly, by grade, which means that the lymphoma cells are immature (lymphoblasts) and quickly dividing, which means the tumour tends to spread rapidly. This is more common than ‘low grade’ lymphoma, where the lymphoma cells are mature (lymphocytes) and dividing relatively slowly. As this type of grows slowly, it’s treated with different medication strategies to high grade lymphoma.
The five most common types of lymphoma found in dogs are:
Approximately 80% of lymphoma in dogs is multicentric, making it the most common type. This type of lymphoma primarily affects the lymph nodes, and it may affect all or some of your dog’s lymph nodes at the same time. You may be able to feel or see some of the lymph nodes, as they typically grow larger and firmer. There are five lymph nodes close to the surface of your dog’s skin (peripheral lymph nodes), that you may be able to feel if they become enlarged.
- Submandibular: Located under your dog’s jaw
- Prescapular: Located in front of your dog’s shoulder
- Axillary: Located in your dog’s armpit
- Inguinal: Located in your dog’s groin
- Popliteal: Located behind your dog’s knee
It is however important to note that lymph nodes can become enlarged in response to infection, inflammation and cancers other than lymphoma.
Accounting for just under 10% of lymphoma in dogs, it’s the second most common form and targets the intestines.
As the name suggests, this type of lymphoma primarily involves the skin, and approximately 6% of dogs with lymphoma will have skin involvement.
An uncommon form, it typically causes the thymus or mediastinal lymph nodes (found by the chest) to become enlarged.
Miscellaneous extranodal lymphoma
Other organs such as the brain, liver, kidneys, bone and eye can also be involved. The term ‘extranodal’ implies that the lymph nodes are not primarily involved.
Dog lymphoma stages
Lymphoma can be subclassified into stages depending on anatomic involvement. Multicentric lymphoma is usually detected at stages three and four, where signs become increasingly obvious:
- Stage one: Single lymph node involved.
- Stage two: Multiple nodes, but only on one side of the diaphragm.
- Stage three: Multiple nodes on both sides of the diaphragm.
- Stage four: Any of the above stages with liver and/or spleen become involved.
- Stage five: The bone marrow, central nervous or other extranodal sites typically become affected by the lymphoma.
Other classification systems also apply, principally:
- Substage a: without clinical signs of illness
- Substage b: with clinical signs of illness
- This classification concerns the specific type of lymphocyte involved in the cancer and can involve either B lymphocytes (B cell lymphoma) or T lymphocytes (T cell lymphoma).
What are the clinical signs of lymphoma in dogs?
The signs of lymphoma will differ slightly depending on what type of lymphoma your dog has. However, the five most common signs to look out for are:
- Swollen lymph glands (you may be able to check for this in the five lymph nodes we listed above)
- Drastic weight loss
- Decreased appetite
- Extreme thirst
For dogs with multicentric lymphoma, the biggest tell-tale sign should be the swollen lymph glands, but do bear in mind that diseases other than lymphoma can cause lymph node enlargement.
A typical symptom with mediastinal lymphoma is difficulty breathing, often caused by the accumulation of fluid within the chest cavity or the lymphoma itself causing compression of the dog’s lungs.
If your dog is suffering from cutaneous lymphoma, then you may notice raised nodules or scaly lesions, which can also appear in the gums, lips and roof of your dog’s mouth.
Diagnosing canine lymphoma
This typically involves taking a sample of one of your dog’s lymph nodes or organs. The quickest way of doing this is via something called a fine needle aspirate. This collects a small population of cells which can then be examined under a microscope by a clinical pathologist. This procedure is quick procedure, designed to cause minimal discomfort and can be done without a general anaesthetic in most instances..
Occasionally a sample taken via fine needle aspiration will be inconclusive (non-diagnostic). If a larger sample is needed, this will entail a biopsy, which allows collection of a bigger sample, with your dog under general anaesthetic. This sample requires careful processing prior to examination, and this process takes several days so there is a longer wait for results of a biopsy, versus those of a fine needle aspirate (which generally are available within 48 hours).
Following your dog’s lymphoma diagnosis, further tests may be run, which can include x-rays, blood tests and urinalysis. This will determine the extent of the disease, as well as your dog’s overall condition.
Lymphoma treatment: chemo, you and your pet
As mentioned above, lymphoma, with few exceptions, is a widespread disease. It’s therefore usually impossible to surgically remove it. Radiation therapy, which also focuses on a small portion of the body, is similarly rarely useful. In order to treat this cancer, we therefore need to treat the entire body, and this involves chemotherapy.
Most dogs with lymphoma suffer from a form of lymphoma that is similar to Non Hodgkin’s Lymphoma (NHL) in people. This type of lymphoma is treated with chemotherapy, and in people it is frequently cured. In order to cure NHL however, chemotherapy must be delivered in very high doses. This means that side effects are inevitable; inappetence, vomiting, diarrhoea, hair loss and lethargy.
Most chemotherapy treatments extend for months, in some cases for over a year. For people, the side effects are arguably worth it, because if you are cured you might live for a few more decades. This is never the case for dogs however who simply do not live that long and moreover, it would be very wrong for us to deliberately make a pet ill.
We therefore use the same chemotherapy drugs in dogs as are used in people (because, obviously, we want to kill the cancer cells), but we use them in much smaller doses, so we can avoid the side effects.
This however, means that we lose the ability to kill all of the cancer cells, and pets with lymphoma are therefore not cured as a result of chemotherapy. Instead, we aim to keep the tumour at bay (in remission) for as long as possible in order to allow your pet to enjoy a normal quality of life while undergoing treatment.
The aim of chemotherapy is therefore to preserve your pet’s normal quality of life for as long as possible.
Protocols and side effects
There are many different protocols (combinations of drugs) that are used to treat lymphoma. They vary in terms of frequency of dosing (and hence visits to the vet), risks of side effects, cost and efficacy. As a general rule, the more intensive protocols – i.e. those involving a variety of different drugs given frequently (generally weekly) are also those with the greatest efficacy.
Treatment options are discussed on a case-by-case basis, as choosing the right chemotherapy protocol for your pet requires careful consideration.
One of the more commonly used protocols involves chemotherapy treatments every week for nine weeks, and then fortnightly for the following six months. If your dog is in remission, then we’ll stop the treatment; and only restart it if your dog relapses.
Because patient response can vary so drastically, we’ll carefully monitor the chemotherapy every step of the way. Please see a separate information brochure on chemotherapy.
As chemotherapy can be excreted, when you’re back at home, it’s important to take extra precautions when handling your pet’s waste. If you’re pregnant, then please avoid all contact with your pet’s waste.
Like in humans, some dogs will suffer from hair loss – especially Poodles, Old English Sheepdogs and other breeds with continuously growing coats.
As the cells in the intestines are usually affected by chemotherapy, it’s not uncommon to notice a change in appetite, stool consistency, or occasional vomiting.
One of the common chemotherapy agents is cyclophosphamide, which can irritate the lining of the bladder. It’s important to monitor your pet’s urination, as it can cause cystitis-like signs.
Epirubicin is another chemotherapy agent, which can cause damage to the heart muscle – the more doses, the higher the risk. We’ll carry out regular heart checks, but it’s important to remember that these types of complications are very uncommon; and your dog is at much greater risk if the lymphoma isn’t treated.
Side effects of chemotherapy
Although we aim to avoid side effects from chemotherapy, approximately 20% of pets receiving chemotherapy will experience some form of side effects. Should your pet experience side effects, we will react by lowering the dose of the drug in question, giving the drug less frequently or simply stopping administration of that drug.
Chemotherapy drugs do not selectively target cancer cells in most instances. Instead they target rapidly dividing cells; they are effective against cancer because in most instances, cancer cells divide very rapidly. Other areas in the body with rapidly dividing cells include the intestines, bone marrow and to a lesser extent, the hair coat. They are therefore the areas most commonly affected when a dog experiences side effects.
Gastrointestinal side effects are most common and generally manifest as a short period of lethargy, and a decrease in appetite occurs two to three days following administration of chemotherapy and lasts for a day or so. Occasionally more severe side effects such as vomiting and diarrhoea can occur.
Chemotherapy can suppress the bone marrow and this, should it occur, will cause a drop in healthy white cell numbers. As these cells are an important part of the immune system, this can predispose your pet to infection. We monitor white cells counts via a blood test prior to each administration of chemotherapy and may withhold chemotherapy or use a lower dose if the white cell count drops significantly.
Hair loss consequent to chemotherapy administration is rare in dogs, but you may notice that clipped areas of hair take a long time to grow back. Occasionally dogs can lose their facial whiskers as well.
If steroids are used alongside the chemotherapy, then you may find your dog wants to eat or drink more – try not to increase their food intake, as weight gain could cause more problems. It is important that they have constant access to fresh water though and they will need to go out to the toilet more often.
Some drugs, such as cyclophosphamide and anthracyclines (doxorubicin and epirubicin) can cause specific side effects Cyclophosphamide, can irritate the lining of the bladder and we may occasionally monitor your pets urine to detect early signs of this side effect
Anthracyclines can cause damage to the heart muscle – the more doses, the higher the risk. We’ll carry out regular heart checks, but it’s important to remember that these types of complications are uncommon.
Lymphoma in dogs survival rate
Unfortunately, as explained above, lymphoma in dogs is not a curable disease.
As lymphoma is such a varied and complex form of cancer, survival rates depend on a range of factors, including the stage at the time of treatment, the choice of treatment, and the aggressiveness. Dogs with stage V disease, or those that are unwell as a consequence of their cancer (substage b) or those that have a T cell lymphoma tend not respond to treatment as well as other dogs with lymphoma.
It is very important to remember that survival times are very variable between individual dogs. Some dogs can respond much better than others. Any quoted survival times are merely a very rough approximation.
Without treatment, the average survival time is three to four weeks. However, with treatment, your dog’s survival time could increase to 12 months.
When we talk about lymphoma, we mention the term “remission” rather than “cure”. Like with all forms of cancer found in humans, if all signs of cancer have disappeared following treatment, then it means your dog is in total remission. Alternatively, if some but not all signs have disappeared, then it means they’re in partial remission.
Unfortunately, dogs in remission still have cancer, but it just means it’s undetectable. Treatment does not cure the disease, but it can buy your dog some time, helping them to feel well again. Sadly, most dogs with lymphoma will relapse, and by that point, the cancer is more resistant to treatment. However, it’s not uncommon to enter remission for a second time, in response to re-instigation of chemotherapy. Unfortunately, with each successive relapse, the lymphoma becomes more and more resistant to treatment and hence responses become progressively lesser and of shorter duration.
No one wants to hear their dog is ill and may not recover, but it’s important to understand the treatment and prognosis. Speak to your referral vet about what to expect over time, and how you can make your dog as comfortable as possible.
By being proactive, you can help to improve your dog’s quality of life, and understand your role in the treatment.
How to ask for a referral to Swift
If you’re worried your dog may have lymphoma, then book an appointment with your GP vet. They can assess your dog, and if they do diagnose lymphoma, then you can ask them to refer you to our internal medicine team for treatment. You can find out more about the referrals process here.
Alternatively, for more information about common illnesses, surgery and treatments for dogs and cats, head on over to our blog.