Intestinal lymphoma is now the most common form of lymphoma in cats. Patients are generally older cats (9 to 13 years of age) with a tendency for male cats to be more predisposed to development of the condition than females. It commonly affects elderly cats with a history of vomiting, diarrhea, weight loss and decreased appetite. An actual mass may develop with intestinal lymphoma or the tumor may be more infiltrative. A mass can potentially cause obstruction in the intestine and lead to a crisis that must be resolved surgically.

Diagnosis is best made by biopsy of the intestine or mass if present. Aspiration and cytology can also be performed if a mass is present. This may not be as definitive as biopsy but is often adequate.
Removing the mass is not curative. Chemotherapy is necessary for best chance at long-term survival.

The more infiltrative forms of intestinal lymphoma do not create actual growths. Affected tissue will appear abnormal on microscopic exam. 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. Lymphoma is graded as high-grade, low-grade, or intermediate-grade. High grade is the most malignant. A biopsy must be obtained to definitively grade lymphoma.

Cats with lymphoma that are not treated with chemotherapy have an average survival time of 4 weeks once the diagnosis has been made.
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.

High Grade Lymphoma:
Treatment for high grade feline lymphoma usually consists of chemotherapy over several weeks. In cases where the tumor is localized and easily accessible, surgery or radiation therapy may be used. The goal of chemotherapy is to induce a complete "remission", by killing most of the cancer cells. "Remission" means that all symptoms of the cancer have temporarily disappeared.
Complete remission is achieved in 50-75% of cats, but cats that achieve only partial remission also feel better according to owners.
The average survival for cats is 6 - 9 months, but the length of remission depends on several factors.

  • The primary site of the cancer
  • How sick an animal is at the start of treatment
  • The feline leukemia status: Cats that test positive for FeLV or FIV have a lower rate of response to therapy, as well as a shorter average survival time when treated.
  • How quickly the tumor is diagnosed (and treated)
  • The extent of disease
Some of the cancer cells do survive in an animal in complete remission, but the numbers are too small to detect. Eventually, these few cells will grow and the cancer will become evident again putting the patient out of remission. Remission can be re-established in most cats by changing the chemotherapy protocol to a new set of chemotherapy drugs. In time, the cancer cells will become resistant to all drugs will no longer respond to therapy. A small percentage of cats that respond will go into a more complete remission that can last for 2 years or longer. This potential response is encouraging and is the reason that treatment for lymphoma in cats is so highly recommended.
Each cat will respond to treatment differently. In general, 50-70% of cats will respond to chemotherapy treatment.
It is rare to cure lymphoma. Chemotherapy increases the chances of long-term survival and quality of life.

Low Grade Lymphoma:
Low grade (small cell) lymphoma occurs most commonly in the gastrointestinal tract of cats. The behavior of low grade lymphoma is different than large cell lymphoma in that it grows more slowly. Typically, oral chemotherapy drugs are used with low grade lymphoma. Most cats (85-90%) will respond to treatment; however it may be a few weeks before a response is seen in some cats. Survival times with treatment for cats with low grade lymphoma average about 1.5-2 years.

Side Effects of Treatment (both forms of lymphoma):
Toxicities can occur (10% risk) with chemotherapy but are generally mild and side effects are minimal. Veterinary chemotherapy is designed to extend a pet's life as long as possible while maintaining a good quality of life. Therefore, the undesirable side effects normally associated with human chemotherapy are both less common and less severe in animals. Side effects such as nausea and anorexia are occasionally reported, but the most common side effect is bone marrow suppression. In 1-2% of patients this can lead to life-threatening infections that require hospitalization. Whiskers are commonly lost, but patients do not experience hair loss seen in humans. Unfortunately, the only way to know whether an animal is going to have a drug reaction is to administer the drug. Some cats never get sick during chemotherapy, while others are very sensitive to the drugs. If a serious reaction occurs, the drugs or doses may be individually adjusted to maintain a good quality of life.