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Lymphoma in Cats

Lymphoma In Cats (Click Here for Lymphoma in Dogs)

Lymphoma in cats, as in dogs, is classified based on the anatomic area that seems most prominently affected by the tumor. In dogs, the most common lymphoma form is the multicentric form, where all the peripheral lymph nodes of the body seem to enlarge at once. While this can certainly occur in cats, the most common feline form of lymphoma is currently intestinal. This was not always the case. Years ago, prior to the widespread use of the feline leukemia vaccine, the mediastinal form (a tumor in the chest cavity) was the predominant lymphoma form and the leading cause of lymphoma was the feline leukemia virus. Now that the virus has become less common, thanks to more cats living indoors, effective vaccination, and readily available testing procedures, causes of lymphoma are more obscure. Cigarette smoke in the home has been found to double a cat’s risk though genetic issues; environmental chemicals and unknown factors remain under consideration. Lymphoma can occur anywhere in the body where there is lymph tissue.

A sick cat undergoes a battery of diagnostic tests and somewhere in the course of the work-up cells are discovered, either in biopsy, aspirate, or even circulating in the blood that tell us that the cat has lymphoma. Now what?

Can my cat be cured?
Theoretically, yes, but practically speaking, no. It is best to focus on a realistic outcome, which is the longest possible survival with good quality life. Different treatment protocols are associated with different disease-free intervals. See below for more details.

How does lymphoma cause death?
Lymphoma is a rapidly growing malignancy that is able to go and grow anywhere where there is lymph tissue, which is virtually every organ in the body. Eventually, the cancer will infiltrate an organ to such an extent that it fails (often this is the bone marrow or the liver). The patient loses his/her appetite, vomits or gets diarrhea, weakens, and dies. At some point the tumor becomes resistant to therapy and no further remissions can be obtained.


The word chemotherapy conjures images of the bald Elizabeth Perkins from The Doctor or the bald and vomiting Campbell Scott in Dying Young. It is unfortunate that many pets (and probably people, too) do not receive chemotherapy based upon these unpleasant images that do not truly represent the current state of treatment response. Chemotherapy simply means therapy using medication (as opposed to therapy using surgery or radiation). We hope that you will open your mind to what decades of research and clinical experience tells us about chemotherapy rather than listening to what Hollywood has to say on the subject. The following are common questions pet owners commonly have regarding chemotherapy for their cat.

Should we see an oncologist?
It is never wrong to see a spet. Lymphoma is such a common malignancy in humans that there are always new drugs, new protocols and experimental therapy that your regular veterinarian may not be familiar with. Seeing a spet may be the best way to present you with all of your options. If you are interested in this, ask your veterinarian for a referral.

Will chemotherapy make my cat sick?
Probably not. Nausea and infection are possibilities but most cats do not experience any such complications. Only 7% of patients require hospitalization due to side effects of chemotherapy. The bottom line here is to know that animals rarely get sick from chemotherapy but that you should know what to do in case of a problem (see later).

Will chemotherapy make my cat lose his hair or go bald?
While whiskers are commonly lost, substantial hair loss is not experienced by animals on chemotherapy for cancer.

How will I know when we have achieved remission?
A patient in remission is indistinguishable from a completely cancer-free patient. The lymph nodes will go down to normal size and if there were any signs of illness related to the cancer, these should resolve. There is approximately a 75% chance of achieving remission regardless of protocol selected.

How will I know when we have lost remission?
The most obvious sign will be that the lymph node enlargement has returned. This means that the cancer is now resistant to the drugs being used and new drugs must be chosen. (This is called a “rescue”.)

How long will my cat have quality life on chemotherapy?
This depends on what protocol you choose and there are many. There are also many factors that influence how an individual will do relative to the “average” response. Important parameters to note when reviewing a protocol are: 1) the disease-free interval (i.e., how long the patient is free from illness; 2) survival time; 3) typical duration of remission; 4) expense; 5) and scheduling.

We will center on intestinal lymphoma as it is currently the most common.

Intestinal Lymphoma

Intestinal lymphoma is now the most common form of lymphoma in cats. The average patient is an elderly cat with a history of vomiting, diarrhea, weight loss, appetite loss or any combination thereof. Patients are generally older cats (median ages ranging from 9 to 13 years depending on the study) with a tendency for male cats to be more predisposed to development of the condition than female cats.

An actual mass may develop with intestinal lymphoma or the tumor may be more infiltrative. An actual mass can potentially cause obstruction in the intestine and lead to a crisis that must be promptly resolved surgically.

Diagnosis of intestinal lymphoma is best made by biopsy and if a mass is present, it can be surgically removed at the time biopsies are taken. Alternatively, the mass can be aspirated (cells removed via syringe) and the cells analyzed in the lab. This may not be as definitive as biopsy but is often adequate; surgery, of course, enables the removal of the growth (if there is one) and relieves the obstruction.

It is important to understand that no matter how localized the tumor appears to be, simply removing the mass is not going to be curative; some kind of chemotherapy is necessary for best chance at long-term survival.

The more infiltrative forms of intestinal lymphoma do not create actual growths; instead the intestine may only be abnormal under the microscope. It is very difficult to distinguish inflammatory bowel disease from lymphoma without a full-thickness biopsy (a full-thickness piece of intestine) obtained via exploratory surgery. A less invasive method of obtaining a sample is via endoscopy, usually adequate for diagnosis but full thickness biopsy samples cannot be obtained this way.

Cats with intestinal lymphoma treated with prednisone alone have a life expectancy of 45 to 60 days. Other protocols using multiple drugs yield much better results (see below for details).
*Lymphoma is graded by the pathologist reading the tissue sample as either high-grade, low-grade, or intermediate-grade. The grade refers to how rapidly the cells appear to be dividing and how malignant they appear with high grade being the most malignant. The grade of lymphoma bears on its response to chemotherapy (see below). It is not possible to determine lymphoma grade from a tissue aspirate; an actual piece of tissue must be submitted for biopsy. As a general rule with lymphoma, higher grades tend to be more responsive to chemotherapy drugs. With feline intestinal lymphoma, however, it is the low-grade cases that are capable of fairly long remissions.

* As with dogs, chemotherapy protocols are associated with minimal side effects. Many protocols have been described for the feline lymphoma patient.

In one study 7 cats were treated with the COP protocol (cyclophosphamide, vincristine, and prednisone). Of these 7 cats, 6 achieved remission with a median duration of remission lasted 19 weeks. The grade of intestinal lymphoma was not considered.
In a study from the Netherlands (Journal of Veterinary Internal Medicine Mar/April 2002), 61 cats with lymphoma were treated with the COP protocol. Of these cats, 75% achieved remission with 51% still disease-free after 1 year and 38% disease-free after 2 years. Median survival time for the group was 266 days. Complete remission was necessary for long term survival; cats with partial remission were unlikely to survive one year. Siamese cats had a more favorable response than cats of other breeds.
In one study, 14 cats were treated with cyclophosphamide, vincristine, and methotrexate. Median survival time was 12 weeks. The grade of the intestinal lymphoma was not considered.
In another study, 132 cats with lymphoma were treated with COP plus doxorubicin, L-asparaginase, and methotrexate (the “CHOP-like” protocol). Of this group 125 cats had intestinal lymphoma. Out of the total 132 cats, 67% achieved remission with a 21-week disease-free interval. Another study using the same protocol on 21 cats with intestinal lymphoma, only 38% achieved remission but these cats had disease-free interval of 40 weeks.
In another study, 25 cats with intestinal lymphoma, 25 of which had high-grade lymphoma, were treated with COP. Those who achieved complete remission had a 30-week disease-free interval. The overall median survival when all 25 cats were considered was only 7 weeks.
As for low-grade intestinal lymphoma, a study of 50 cats included 36 treated with prednisone and chlorambucil. Here, 69% achieved complete remission for a median duration of 20.5 months.

By Wendy C. Brooks, DVM, DipABVP
Educational Director,

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