What is it?Lymphoma is a cancer of a type of white blood cell called a lymphocyte. Like in other types of cancer, the cancer cells multiply uncontrollably due to changes or mutations in their DNA. Lymphoma is different to leukaemia: in leukaemia, the cancer cells arise first in the bone marrow and the blood, whereas in lymphoma, the cancer arises most commonly in the lymph nodes. It can also affect other organs such as the liver, spleen, intestines, skin and eyes.
Why is it important?Lymphoma is one of the most common cancers seen in dogs. If detected early, there is a higher chance that any treatment will be successful.
What's the risk?Lymphoma most commonly develops in middle aged to older animals, however it is a cancer that unfortunately does sometimes affect young animals too. Male and female dogs are equally affected. Like in humans, genetics are likely to play some role in making certain dogs more predisposed to developing lymphoma than others, however, little is known about what genes play a role in this. Any dog breed can develop lymphoma, though studies have found it is more commonly seen in certain breeds, such as rottweilers, boxers, dobermans and Bernese mountain dogs.
What happens to the dog?In the most common type of lymphoma, lymph nodes become enlarged in one or more areas of the body, most commonly lymph nodes under the skin, but also lymph nodes inside the chest or abdomen. Dogs have many clusters of lymph nodes under the skin, including the under the jaw, in the armpits, in front of the shoulders and behind the stifles (knees). When these swellings initially develop the dog may be perfectly well, but on other occasions is unwell, may be losing weight, have a reduced appetite or be drinking excessively. However lymphoma in general is considered to be a 'systemic' disease, affecting many areas within the body. It may initially just affect lymph nodes in one part of the body, but then spread to involve the spleen, liver, and in advanced disease, bone marrow. There are less common forms of lymphoma which initially do not affect lymph nodes but start as lumps within the skin, or internal organs such as the kidneys. Also, sometimes lymphoma can trigger other diseases, such as autoimmune diseases where the body’s immune system attacks healthy tissues within the body. One example of this is a disorder in which red blood cells are destroyed, sometimes causing a life threatening anaemia (low red blood cell count).
How do you know what's going on?
If your vet is suspicious of lymphoma, they may wish to take a sample of any swellings that have developed - this is most commonly by fine needle aspirate (FNA). This involves inserting a needle into the swelling to take a sample which can be put onto a slide and analysed under a microscope.
It is likely a blood sample will be taken to assess blood cell counts - if the disease is advanced, there may be cancer cells within the blood. Also, dogs with lymphoma are often anaemic. Other changes in blood tests may be seen if the liver or kidneys are affected. Often dogs with lymphoma have high levels of calcium in their blood, which causes them to be more thirsty than normal and can lead to other problems, such as the formation of bladder stones. If lymphoma is confirmed, more tests can be done in order to find out more about the types of lymphocytes affected, as this can affect the prognosis and treatment. Investigations may be carried out in order to 'stage' the lymphoma. This usually involves some form of imaging: x-rays, ultrasound, CT or MRI scans, or a combination of these, to assess internal organs for involvement. Further samples may be taken from internal organs by FNA or biopsy.
The stages of lymphoma are as follows: