Overview of Feline Lymphosarcoma (Lymphoma)
Lymphosarcoma (lymphoma) is a malignant cancer that involves the lymphoid system. In a healthy animal, the lymphoid system is an important part of the body’s immune system defense against infectious agents such as viruses and bacteria. Lymphoid tissue normally is found in many different parts of the body including lymph nodes, liver, spleen, gastrointestinal tract and skin.
Classification of Lymphosarcoma in Cats
Lymphosarcoma is classified according to the location in the body in which the cancer begins.
The multicentric form occurs in the lymph nodes.
The gastrointestinal form occurs in the stomach, intestines, liver and lymph nodes in the abdomen.
The mediastinal form occurs in the mediastinum, in front of the heart in an organ called the thymus. Hence this form of lymphosarcoma sometimes is called thymic lymphoma.
The cutaneous form occurs in the skin.
Acute lymphoblastic leukemia occurs when the disease starts in the bone marrow.
Miscellaneous forms of lymphosarcoma are less common and include those that begin in the nervous system, nasal cavity or kidneys.
Currently in the USA, gastrointestinal lymphoma is the most common form. Historically, mediastinal lymphosarcoma occurred most frequently in young cats infected with feline leukemia virus, but reports of young cats with FeLV positive lymphoma are less common than in the early 1980’s. These cats may have involvement in other areas of the body, such as the bone marrow. The gastrointestinal form of lymphosarcoma most commonly affects older cats that are not infected with the feline leukemia virus.
Recently, research has shown that cats that live in smoking environments are 2 to 4 times more likely to develop lymphoma than cats that live in smoke-free environments. The exact mechanism is not understood.
Lymphosarcoma occurs in middle-aged to older cats. No breed of cat is known to be at a higher risk for lymphosarcoma than other breeds. Males and females of both species are affected equally. Infections with both feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) have been shown to increase the risk of developing lymphosarcoma. Cats infected with FeLV often develop lymphosarcoma at a young age.
Symptoms in cats with lymphosarcoma depend primarily on the location of the tumor cells. Symptoms include enlargement of external lymph nodes, vomiting, diarrhea, loss of appetite, weight loss, lethargy, difficulty breathing and increased thirst or urinations. Cutaneous lymphosarcoma can cause redness or flakiness of the skin, ulceration (especially near the lips and on the footpads), itchiness (pruritus) or lumps in the skin.
Diagnosis of Lymphosarcoma (Lymphoma) in Cats
Diagnostic tests are needed to identify lymphosarcoma and exclude other diseases. These tests may include:
Complete blood count (hemogram or CBC) to identify anemia, low platelet count, or abnormal lymphocytes in the circulation.
Serum biochemistry to evaluate the general health of your pet and to determine the effect of lymphosarcoma on other organ systems. Hypercalcemia (high serum calcium concentration) may occur with lymphosarcoma and can be a clue to the presence of malignancy.
Urinalysis to evaluate kidney function and identify urinary tract infection.
Chest X-rays to evaluate for mediastinal lymphosarcoma or enlargement of lymph nodes in the chest.
Abdominal X-rays to evaluate for enlargement of the liver and spleen, which may be infiltrated with malignant lymphocytes.
Abdominal ultrasound to evaluate for enlargement of the liver, spleen, or lymph nodes in the abdominal cavity.
Feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) tests.
Fine needle aspirate and microscopic analysis of an enlarged lymph node.
Biopsy of a lump or enlarged lymph node.
Endoscopy and biopsy of the gastrointestinal tract.
Fine needle aspiration and microscopic analysis of bone marrow to evaluate for invasion of malignant lymphocytes into the bone marrow.
Treatment of Lymphosarcoma (Lymphoma) in Cats
Chemotherapy (most common form of treatment)
Radiation therapy (for localized disease)
Surgery (for localized disease)
Seek veterinary care promptly if you detect lumps below your pet’s skin in the neck, shoulders, armpits, or back legs or if your pet has vague symptoms of illness such as loss of appetite, lethargy, and weight loss. Watch your pet for vomiting, diarrhea and development of infections.
The best prevention is to avoid infection of cats with FeLV and FIV by limiting their exposure to other cats of unknown status. Also, smokers should consider quitting smoking or only smoking outside.
In-depth Information on Lymphosarcoma (Lymphoma) in Cats
Other diseases can mimic the signs of lymphoma. Some of these may include:
Other diseases that cause enlargement of the lymph nodes may include:
Bacterial, viral or fungal infections. An infection can cause enlargement of one or more lymph nodes. In localized infections, the lymph node that normally drains the affected region of the body typically becomes enlarged.
Immune-mediated diseases. These diseases occur when the immune system fails to recognize parts of the body and begins to attack normal tissues. Systemic lupus erythematosus is an example of a body wide immune-mediated disease.
Severe skin diseases (especially chronic bacterial infections, or systemic demodectic mange) can cause enlargement of external lymph nodes.
Other cancers can cause enlargement of one or more lymph nodes due to spread (metastasis) of the tumor by way of the lymphatic system.
Other diseases that can vomiting, diarrhea, weight loss, decreased appetite include:
Infections. Viruses such as the coronavirus that causes feline infectious peritonitis can cause gastrointestinal symptoms.
Inflammatory bowel disease (inflammation of the intestine due to a variety of causes) can cause vomiting and diarrhea and prevent proper digestion.
Other intestinal tumors (intestinal adenocarcinoma, intestinal leiomyosarcoma, mast cell tumor) can cause vomiting or diarrhea.
Metabolic diseases such as hypoadrenocorticism (“Addison’s disease”), diabetes mellitus, liver disease, or kidney disease.
Other diseases that can cause difficulty breathing may include:
Heart failure with fluid accumulation in the lungs (pulmonary edema) or in the chest cavity (pleural effusion).
Respiratory infections such as pneumonia can cause coughing, increased respiratory rate, and difficulty breathing.
Tumors originating in the lungs or those that have spread (metastasized) to the lungs from other sites can cause difficulty breathing.
Veterinary care should include diagnostic tests and subsequent treatment recommendations.
Diagnostic tests are needed to recognize lymphosarcoma and exclude other diseases. Tests may include:
A fine needle aspirate using a regular syringe and needle can be performed to obtain cells from enlarged lymph nodes for microscopic analysis (called cytology). Fluid that has accumulated in the chest also can be withdrawn for analysis. With the aid of ultrasound examination, needle aspirates also can be obtained from internal abdominal organs (e.g., liver, kidney, spleen) or from a mediastinal mass in the chest.
A biopsy specimen can be collected if the diagnosis cannot be made on the basis of cytologic evaluation of a fine needle aspirate. A biopsy specimen can be obtained by one of several different methods. A lymph node biopsy can be collected by a taking a core of tissue with a needle biopsy instrument (so-called “Tru-Cut needle”), by making an incision to take a small piece of a lymph node or by removing the entire lymph node surgically. Needle biopsies can be obtained using sedation and local anesthesia but the lymph node removal requires general anesthesia.
Biopsy specimens can be collected by endoscopy when gastrointestinal lymphosarcoma is suspected. Endoscopy involves the use of a long flexible scope and light source to examine the inner surface of the stomach and intestine. Several areas in the stomach and intestine are biopsied and submitted for examination by a veterinary pathologist. Biopsies also can be taken during an exploratory abdominal surgery, but endoscopy is much less invasive and takes less time. The biopsies taken during endoscopy are very small and may not be conclusive. If these samples are not conclusive, exploratory abdominal surgery can be performed to take larger biopsies from the gastrointestinal tract and to evaluate other abdominal organs such as the liver, spleen, and kidneys.
A complete blood count (hemogram or CBC) is performed to evaluate for anemia, low platelet count, or abnormal circulating lymphocytes.
Serum biochemistry tests can be performed to evaluate the general health of your cat and determine the effect of lymphosarcoma on other organ systems. High blood calcium concentration (hypercalcemia) occurs in some animals with lymphosarcoma and can cause increased water consumption, increased urinations, and kidney dysfunction.
Urinalysis can be performed to evaluate kidney function or identify presence of urinary tract infection.
Chest X-rays allow evaluation of your pet for a mediastinal mass, enlarged lymph nodes in the chest, or involvement of the lungs in the disease process. The mediastinum (a collection of lymphoid tissue located in front of the heart) can be the primary disease site in cats with FeLV-induced lymphosarcoma. In addition, lymphosarcoma can be associated with fluid accumulation in the chest cavity. This fluid can be removed with a needle and syringe to allow the pet to breathe better and to obtain fluid for microscopic analysis.
Abdominal X–rays can be used to identify enlargement of the liver, spleen, or kidneys that can occur in some animals with lymphosarcoma.
Abdominal ultrasound examination can be used to identify enlargement of abdominal organs and lymph nodes in the abdomen. This procedure can also be used to guide the needle during biopsy procedures.
Feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) tests are performed in cats with suspected lymphosarcoma because both viruses have been shown to increase the risk of developing lymphosarcoma. FeLV infection typically is seen in younger cats with lymphosarcoma. The virus does not interfere with a cat’s ability to respond to chemotherapy, but it does tend to shorten their survival time. Feline immunodeficiency virus infection usually is seen in middle-aged to older cats with lymphosarcoma. It has not been determined whether or not this virus adversely affects survival time in treated cats.
A bone marrow aspirate is performed to determine if the disease process has affected the bone marrow. The bone marrow is responsible for making red and white blood cells and platelets. Bone marrow aspirates usually are performed using sedation and local anesthesia. The most common sites used to obtain bone marrow are the humerus (just below the shoulder) and the hip (ileum). Response to treatment may be adversely affected if lymphosarcoma is found in the bone marrow.
Treatment for lymphosarcoma may include one or more of the following:
Chemotherapy is the most commonly recommended treatment for lymphosarcoma. A cat is said to be in remission when clinical evidence of the cancer disappears after treatment. Achievement of remission by chemotherapy does not mean that the cat is cured, and cancer is likely to return if treatment is discontinued.
Several different drugs alone or in combination have been used during the past 30 years to treat lymphosarcoma.
The commonly used drugs include:
Prednisone (a cortisone-like drug)
Depending upon the drug, treatment can be given by injection under the skin (subcutaneously), intravenously or by mouth (orally). Combinations of these drugs work better than a single drug.
A protocol is an outline of the treatment plan consisting of:
What drugs are used
Dosages of the drugs
Route of administration
How frequently treatments are administered
How long treatment is continued
Several different protocols have been used to treat lymphosarcoma and actual treatment may vary from veterinarian to veterinarian. In addition, adjustments to the protocol may be made depending upon the patient.
The most common adverse effects of cancer chemotherapy are gastrointestinal symptoms (e.g., loss of appetite, vomiting, diarrhea) or a decreased white blood cell count, which may increase the risk of secondary infection. Cats generally do not experience the hair loss that affects humans undergoing chemotherapy. In fact, cats usually tolerate chemotherapy much better than do humans. The risk of a serious adverse effect that would require hospitalization is small (perhaps 5 to 10 percent). If adverse effects do occur, your veterinarian may change the protocol to prevent these adverse effects during future treatments.
Fifty to sixty percent of treated cats achieve remission with an average survival time of 6 to 8 months. Ten to fifteen percent of cats treated for lymphosarcoma survive 2 years or more.
It often is possible to treat pets successfully a second time using different drugs or radiation therapy when relapse occurs. Different treatment approaches are necessary because the malignant lymphocytes have become resistant to the drugs used previously. It is more difficult to treat animals experiencing a second or third relapse and remission times generally are shorter.
In some circumstances, radiation therapy may be recommended in addition to or instead of chemotherapy. Radiation therapy requires referral to a specialty institution that offers radiation therapy because it requires specialized equipment and training.
Radiation therapy may be recommended if the pet has lymphosarcoma localized to a single site. It is essential, in this situation, to conduct a thorough search for other areas of involvement. Chemotherapy should be used in conjunction with radiation therapy if other areas of involvement are suspected or if a cat with lymphosarcoma is infected with FeLV or FIV. A full course of radiation involves a total of 10 to 16 treatments given 3 to 5 times a week. Adverse effects vary depending upon the region of the body treated and the number of treatments given. Animals must anesthetized for each treatment to prevent movement during radiation exposure.
Radiation can be used if lymphosarcoma is causing in a specific location of the body is discomfort or clinical signs. This type of treatment is called palliative radiation therapy, and involves use of a few large doses of radiation to the affected area. Adverse effects usually are minimal with this type of radiation therapy.
Surgery rarely is used in the treatment of lymphosarcoma, and is more commonly used to make a diagnosis of lymphosarcoma (to obtain biopsy specimens for examination by a veterinary pathologist).
Follow-up Care for Cats with Lymphoma
Promptly seek veterinary care if your animal develops signs of vague signs illness (e.g., loss of appetite, lethargy, unexplained weight loss) or abnormal swellings under the skin of the neck, shoulders, armpits or thighs.
Cats with lymphosarcoma may have poor appetites due either to the cancer itself or the effects of chemotherapy. Cats with poor appetites should be encouraged to eat and offered a variety of different foods. Some medications can be prescribed to try and increase appetite.
Cats with lymphosarcoma may develop vomiting and diarrhea due to the effects of chemotherapy. Antacids and anti-nausea drugs may be used to help prevent nausea and vomiting. Dietary modification and antibiotics may be used in cats that develop diarrhea. A bland diet such as boiled chicken or hamburger and rice may be helpful.
The white blood cell count may decrease after chemotherapy and increase the risk of secondary bacterial infection. Signs to watch for include lethargy and loss of appetite. A rectal thermometer can be used to monitor the cat’s temperature at home. A temperature of greater than 102.5°F in an animal that is lethargic is cause for concern. Seek veterinary care promptly if you think your pet has an infection. Hospitalization to provide fluid therapy and intravenous administration of antibiotics may be necessary. Your veterinarian will monitor your pet’s white blood cell count during chemotherapy and may adjust drug dosage or schedule based on the white blood cell count.
Cats should be tested for FeLV and FIV infection when first acquired. Cats should be kept indoors to minimize the risk of being exposed to these viruses. Outdoor cats can be vaccinated against FeLV, but the vaccine is not completely protective.