LYMPHOMA IN CATS
Lymphoma is, at this time, the most common malignancy of the cat accounting for as much as 30% of all feline cancers. Luckily, it is just as responsive to medication as it is in the dog and prolonged remissions are common. This article reviews the common forms of lymphoma in the cat including diagnosis and treatment expectations.
As we have discussed, lymphoma is a cancer made of lymphocytes and these lymphocytes readily travel throughout the body via the lymph system. Because of all this traveling, lymphoma is only a localized problem in rare situations so surgery and radiotherapy are not appropriate as sole treatments. To reach cancerous lymphocytes in all the places they have gone, medication (chemotherapy) is necessary because medication can be carried all over the body via the circulation. Treatment of lymphoma is going to involve pills and/or injections for your cat regardless of which form of lymphoma has been diagnosed.
CLASSIFICATION BY ANATOMICAL LOCATION
As mentioned earlier in this article series, lymphoma can develop anywhere where there is lymph tissue and virtually all organs have some bits of scattered lymph tissue associated with them. It is not clear why some areas seem to be especially vulnerable to the development of lymphoma over others.
In the past, prior to the development of the vaccine for the feline leukemia virus, the intestinal form of lymphoma was unusual but now intestinal lymphoma accounts for 50-70% of all cases of feline lymphoma.
Cats with intestinal lymphoma tend to be senior cats (age 9-13 years on average) with a chronic history of weight loss, vomiting, diarrhea or all three. Appetite is variable which means it may be normal, excessive, reduced, or non-existent.
Intestinal lymphoma may be present as a distinct mass or growth or group of growths, or as a more subtle infiltration of cancerous lymphocytes into the delicate membranes of the bowel lining. Infiltrative lesions, which are often invisible to the naked eye, generally respond to chemotherapy; surgery is not necessary or even helpful. Distinct masses, however, can cause an acute obstruction and may require surgical removal to relieve this potential emergency. Removing these masses does not control the cancer and chemotherapy is still needed after the surgical site has healed.
Ultrasound without biopsy?
Further, often the appearance of the intestine and lymph nodes is ambiguous. In this situation, the liver can be aspirated despite its normal appearance. Often lymphoma can be found “hiding out” there. Again, if a diagnostic aspirate is obtained via ultrasound, it is not necessary to pursue surgery or endoscopy
High Grade versus Low Grade
One of the advantages of having an actual tissue sample is the ability to grade the malignancy of the lymphoma. Lymphoma is graded by the pathologist reading the biopsy 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 may be possible to grade a lymphoma with an aspirate sample but it is vastly easier with an actual chunk of tumor. 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 achieve remission easier and for prolonged periods of time.
Fortunately, most feline lymphoma is the low grade (also called “lymphocytic”) form of lymphoma. This form behaves much more like inflammatory bowel disease, and, in fact, treatment for severe IBD is largely the same as for low grade intestinal lymphoma. Approximately 70% of cats with this form of lymphoma will achieve remission and the median survival time is 23-30 months. Treatment for this form of lymphoma generally involves oral medication: prednisolone and chlorambucil. Many people opt to treat with these two medications based on ultrasound appearance of the GI tract, playing the odds that there will be a response. Given the expense of more accurate diagnostics, this may be a reasonable alternative approach.
Unlike other forms of lymphoma, renal lymphoma has a strong association with tumor spread to the nervous system (brain or spinal cord). This makes for an unpleasant complication and, unfortunately, this occurs in up to 40% of renal lymphoma cats.
The mediastinum is not a structure with which most people are familiar. Most people know the chest cavity contains the heart and lungs and some other affiliated structures. But these organs are not just loose and flopping around in the chest and they are not simply held in place by gravity. The mediastinum is a sheet of connective tissue that bisects the chest, contains the heart, esophagus, trachea and another other central structures similar to a vacuum packed plastic bag. The mediastinum divides the chest into right and left halves and stabilizes the location of the organs in the middle.
Of note in the lymphoma situation are the thymus gland (generally atrophied in adult animals) and the mediastinal lymph nodes. These are lymph system tissues and become the seat of mediastinal lymphoma.
Chest radiograph of a cat with area of the thymus and mediastinal lymph nodes marked.
When these lymph structures fill with lymphoma, the normal fluid drainage of the chest is hampered and fluid begins to back up in the chest creating what is called a “pleural effusion.” This fluid takes up space in the chest that would normally go to expansion of the lungs and when the lungs cannot expand, the patient cannot breathe. Shallow rapid breaths, possibly with the mouth open, result and the patient must focus on breathing rather than normal activities including eating. The fluid can be tapped off the chest using a needle and a sample can be sent to the laboratory for analysis. Usually lymphoma cells can be found in the fluid if they are present. Treatment is chemotherapy as with the other forms of lymphoma.
Most mediastinal patients are young (less than 5 years old) adults and most (80%) are feline leukemia virus positive. Siamese cats seem to be predisposed to this form of lymphoma. In the days prior to the release of the vaccine for the feline leukemia virus, mediastinal lymphoma was the most common form of feline lymphoma. Today, we rarely see it. Cats that are positive for the leukemia virus tend not to live as long because of other complications from the infection but remission is readily obtained regardless of the viral infection in most cats.
Cat with nasal lymphoma before chemotherapy, and the same cat two weeks after chemotherapy
The nasal form of lymphoma is one of the more rare forms of lymphoma but bears mentioning because it is the only form that is potentially localized to one area. Cats with nasal lymphoma typically have a nasal swelling, sneezing, and nasal discharge.
Localized disease (i.e. the tumor in the nose) can be treated with radiotherapy or with chemotherapy. In general, as with other forms of lymphoma, the disease is assumed to have traveled to other (“distant”) areas of the body. Because distant disease is addressed with chemotherapy and it is assumed that lymphoma patients have distant disease along with their local disease, most nasal lymphoma patients receive chemotherapy.
Prolonged remission times (median survival times over 500 days) are possible with treatment.
Page last revised: 9/3/2019