Cats are experts at hiding disease, sleeping a little more and doing a little less. A diagnosis of lymphoma can be a complete surprise in a cat who seems a little off colour. But lymphoma is actually a remarkably common disease in cats.

What is lymphoma?

Lymphoma is the most common cancer in the cat, causing 33% of cat tumours(1). It is sometimes called lymphosarcoma. Cancer is caused by a mutation in the DNA of a cell causing abnormal cell function or growth. In the case of lymphoma, this is caused by an abnormal proliferation of lymphocytes, a type of white blood cell. 

Lymphocytes are part of the immune system. They protect the body by recognising foreign material or organisms that cause disease and forming antibodies to destroy them. They also remember threats and remain alert to new or recurrent infections. As lymphocytes travel all around the body, lymphoma can occur in many sites.

Symptoms vary, depending on the tumour site. Most cats will lose their appetite and consequently lose weight. Some cats become lethargic and depressed. 

Which cats are more likely to get lymphoma?

Most cats who develop lymphoma are 9-13 years old. Male cats have a higher risk, as do cats who live with a cigarette smoker. Two viral infections, feline leukaemia virus (Felv) and feline immunodeficiency virus (FIV) increase the risk of lymphoma. The incidence of these viruses has reduced because of vaccination and neutering, but the number of lymphoma cases is still rising (2)

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Types of lymphoma

Alimentary 

The most common form occurs in the stomach and intestines.  

Older cats are usually affected. Weight loss can be profound. They may vomit, have diarrhoea or constipation, and pass blood in their stool. A vet may feel a mass in the abdomen. 

Mediastinal 

These tumours affect the chest of younger cats, the average age is 5 years, but it can occur under 1 year. Siamese and Oriental cats have a higher risk of this disease (2).

Affected cats may have rapid or laboured breathing. They may open their mouths to breathe, this usually suggests a severe lung or airway disease as cats do not pant like dogs. Affected cats are often restless with pale or grey, blue gums.

Multicentric or nodal  

Cats have lymph nodes all over the body. Some are just under the skin and easily felt if enlarged. Multicentric lymphoma causes lymph node swelling so they can be felt at the angle of the jaw, in the neck, behind the elbows and knees. 

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Renal

Lymphoma in the kidney often causes vomiting, weakness and excessive drinking and urination. 

Miscellaneous

Lymphoma may affect the lung, heart, brain, bone marrow, skin and nose. The tumours may be solitary or diffuse. Symptoms vary depending which organs are affected. 

How is lymphoma diagnosed?

If your vet suspects lymphoma, further investigation is necessary. Imaging with x-ray or ultrasound will identify abdominal and chest masses. Lymphoma must be confirmed by a pathologist looking at cells under the microscope. Therefore, samples must be taken.

Fine needle aspiration (FNA) is a cheap, low risk, minimally invasive procedure. A needle is placed into the mass or organ to harvest cells. FNA is only possible when affected areas are accessible. This technique does not always yield sufficient cells to gain an accurate diagnosis. Unfortunately, lymphocytes can be seen in high numbers in inflammation as well as cancer, so it can be hard to differentiate the two diseases with a few cells. 

Endoscopy can be used to obtain biopsies in alimentary lymphoma. This is less invasive than surgery but may not be definitive as biopsies do not include the full thickness of the stomach or intestine. 

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Surgical biopsy may be required, as a larger section of tissue can be removed. This allows the pathologist to carry out tests such as immunohistochemistry. These advanced techniques provide more accurate information that can lead appropriate treatment choices. 

Blood tests are taken to assess the health of the cat. Most cats with lymphoma have anaemia. Some will have biochemical changes showing organ dysfunction, such as low blood protein when lymphoma affects the function of the intestine or kidney.

The results of investigations are used to determine the best course of action for the individual cat. Complete cure is unlikely, but remission may be possible for 2 months to 3 years depending on the tumour. Remission means a temporary reduction in signs of disease.

The factors to consider when deciding on treatment include: 

  • malignancy and prognosis of the tumour 
  • health of the cat 
  • extent of the disease
  • temperament of the cat and whether they will cope with intervention
  • and the pet owner’s situation, financially, practically and emotionally. 

Having an informed idea of the treatment options allows these factors to be considered.

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Treatment 

Chemotherapy is the mainstay of lymphoma treatment. This treatment produces excellent results for low-grade lymphoma with 80-90% remission for 22 months(2) . Only 10% of cats suffer adverse reactions, with vomiting, diarrhoea or loss of appetite. Cats do not lose their hair and are less likely to become ill than people when treated with chemotherapy.

Low grade alimentary tumours can be treated with two long term oral drugs, prednisolone and chlorambucil. 70% of cats will achieve remission for 2-3 years using this protocol. The cat will need regular blood tests. Chemotherapy drugs (like chlorambucil) kill cells, cancer cells and healthy cells so they must be carefully handled. They must not be accessible to children, owners should wear gloves to administer them, chemotherapy should not be considered in an aggressive cat.

High grade alimentary tumours are less responsive to treatment with 25-50% of cats achieving remission for 2-9 months with more intense protocols. These protocols involve weekly injectable drugs as well as oral medications administered at home.  

Mediastinal lymphoma is commonly associated with Felv, infection reduces the average survival time (with treatment) from 9-12 months to 3 months. 

Cats with renal lymphoma have an average survival time of 3-6 months with treatment. This tumour commonly spreads to the nervous system.  In the case of a solitary tumour, surgical removal is possible. However as lymphocytes travel around the body distant disease may remain. Surgery may also be necessary if an intestinal tumour blocks the gut.

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Radiotherapy can be used to treat a single tumour, this may be useful for nasal tumours. Chemotherapy is often required after surgery or radiotherapy.  

Chemotherapy may not be the right choice for every cat. In this case, prednisolone a steroid drug can be used as palliative care. This can reduce the growth of lymphoma and reduce the inflammation around a mass. 

What you can do at home  

Loss of appetite is common with lymphoma so tempt the cat to eat with warmed food, offering multiple feeds and attention to help to maintain bodyweight. Provide a warm, peaceful place to hide away and rest. 

Many cases of lymphoma respond to treatment. The diagnosis does not have to be devastating. Each case must be considered individually as the treatment decisions must be made in the best interests of the cat and owner. As lymphoma is a model for human disease, there is a lot of research into new, less intense treatment regimes (3). Vaccination against feline leukaemia virus can reduce the risk of lymphoma.

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References and further reading:

1. Louwerens M, London CA, Pedersen NC and Lyons LA. Feline lymphoma in the post‐feline leukaemia virus era (2005). Journal of Veterinary Internal Medicine19: 329– 335

2. Limmer S, Eberle N, Nerschbach V, Nolte I and Betz D. Treatment of feline lymphoma using a 12 week, maintenance-free combination chemotherapy protocol in 26 cats, (2016). Veterinary and Comparative Oncology. 14. (S1):21-31
3. Paulin MV, Couronne L, Beguin J, Le Poder S, Delverdier M, Somin M, Bruneau J, Cerf-Bensussan N, Malamut G, Cellier C, Benchekroun G, Tiret L, German AJ, Hermine O and Freiche V. Feline low-grade alimentary lymphoma:an emerging entity and a potential animal model for human disease. (2018). BMC Veterinary Research. 14:306