Lymphoma In Cats

Lymphosarcoma, more commonly called lymphoma, is a form of cancer affecting the immune system. As with all cancers, the initiating event is a change in the structure of the DNA of the affected cells. Lymphoma can arise spontaneously, as it probably does in most cases, or following infection with the feline leukemia virus. Whichever the cause, a normal white blood cell called a lymphocyte loses the ability to limit both its lifespan and the number of times it divides, resulting in the growth of large masses of tumorous tissue.

There are several different classification schemes for lymphoma in cats, but they are most commonly grouped as:

• alimentary (affecting the digestive tract)
• mediastinal (masses in the anterior chest)
• multicentric (multiple tumors growing in lymph nodes throughout the body)
• extranodal- essentially all tumors not fitting into the categories above

To a certain extent, the behavior of an individual cat's lymphoma will depend on the location in which it arises.

Feline Leukemia Virus (FeLV) is an unpleasant and potentially very serious infection of cats, but also is very interesting in its behavior. It is part of the retrovirus family, and causes disease by actually inserting itself into the host animal's DNA, causing profound suppression of the immune system, and often malignant transformation of cells, leading to a greatly increased risk of cancer. It is spread between cats in bodily secretions, and so can be passed on through grooming, shared feeding bowls, or from mother to kitten. Once infected, a cat has approximately a 50% chance of overcoming the infection, although it appears the virus is never eliminated from the body but rather becomes latent.

Because of the cancer-causing potential of this virus, some cats with lymphoma will test positive for FeLV. When FeLV was first discovered in the 1960s, a very large percentage of cats with lymphoma did indeed have concurrent FeLV infection. However, with successful containment of infection in recent decades as well as the availability of effective vaccines the incidence of FeLV infection in lymphoma in cats has decreased dramatically.

Amazingly, every domestic cat is born with a copy of an ancient FeLV strain incorporated into their genetic makeup. This endogenous FeLV (eFeLV) must have infected ancestors of our pet cats thousands of years ago, but a balance has been struck between the host cat and its eFeLV such that this strain is no longer a cause of disease in our pets.

Because of the many sites which can be affected by lymphoma, the range of symptoms seen in cats is very large, ranging from paralysis (spinal cord extranodal form) to vomiting (alimentary), palpable lumps under the skin (multicentric), or breathing difficulties (mediastinal).

Lymphoma is on the list of differential diagnoses for cats presenting to veterinarians with these and other signs, and diagnosis relies on first visualizing and then identifying the tumor using some combination of exploratory, imaging, and/or biopsy techniques. Your veterinarian will also conduct a blood test to detect FeLV if present.

Because of its diverse nature, feline lymphoma has various different treatment options depending on its location and other factors such as the general health of the patient. While lymphoma of the eye (ocular lymphoma) requires surgical treatment, nasal lymphoma may respond well to radiotherapy. Alimentary, mediastinal, and other presentations are most often treated with chemotherapeutic drugs, sometimes with a highly successful outcome.

The prognosis for some forms of lymphoma is very positive, for example nasal lymphoma has very long survival times when treated appropriately. Response to treatment is by far the best indicator of prognosis for animals treated medically, which unfortunately is of little help to the veterinarian or owner when trying to decide whether to embark on a course of potentially costly treatment. Cats with all forms of lymphoma that test positive for FeLV unfortunately have a poor prognosis.

The aim in treating this disease is to maximize the cat's quality of life for as long as possible, not in most cases to cure the disease. In veterinary medicine we do not generally expect our patients to have to tolerate the severe side effects of very aggressive cancer treatments which we might agree to subject ourselves to in similar circumstances. Without the animal's consent, and allowing for the fact that our pets very much 'live in the moment', allowing them to enjoy their lives for as long as they are in good health is what we aim to do. For this reason, a cure is rarely achieved, but it does sometimes happen that feline lymphoma can go into complete remission.

If you have lost a beloved pet because of lymphoma or any other illness it is perfectly natural and normal to experience a profound sense of loss. Bereavement over the death of a pet will hit many of us just as hard as losing any other family member. Don't be ashamed or embarrassed- find someone to speak to about your feelings, whether it is a friend, family member, or counsellor. Some psychologists and psychotherapists specialize in pet bereavement counselling, and if you can find one of these specialists in your area they can be a huge help.

• Humane Society- Dealing With Pet Loss