Overview of Canine 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. Lymphosarcoma is classified according to the location in the body in which the cancer begins. Lymphosarcoma is commonly abbreviated as “LSA”.
Types of Lymphoma in Dogs
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.
In dogs, the most common form of lymphosarcoma is the multicentric form (80 percent of all dogs with lymphoma have this form). Frequently, owners notice lumps under the neck or in other locations. These lumps represent the enlarged lymph nodes. Dogs still may feel normal at this point in the disease or may have vague symptoms such as lethargy or decreased appetite. The other forms of lymphosarcoma are much less common in dogs.
Lymphosarcoma occurs in middle-aged to older dogs. Breeds of dogs that are at a higher than average risk of developing this disease include Rottweilers, Scottish terriers, Golden retrievers, Basset hounds, and German shepherds. Males and females are affected equally. In dogs, there may be a genetic basis for this disease and, in certain breeds, some families several closely related animals have been affected. An association between development of lymphosarcoma and exposure to the herbicide 2,3-D may exist.
Symptoms with lymphosarcoma depend on 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 or lumps in the skin.
Diagnosis of Lymphosarcoma (Lymphoma) in Dogs
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 Dogs
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.
In-depth Information on Lymphosarcoma (Lymphoma) in Dogs
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 parvovirus 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 (e.g., 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.
In-depth Information on Diagnosis
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 (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 (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 your pet for anemia, low platelet count, or abnormal circulating lymphocytes.
Serum biochemistry tests can be performed to evaluate the general health of your dog 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 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 some dogs with 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 dog 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.
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.
In-depth Information on Treatment
Treatment for lymphosarcoma may include one or more of the following:
Chemotherapy is the most commonly recommended treatment for dogs with lymphosarcoma. A dog 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 animal 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 in dogs.
The commonly used drugs include:
Prednisone (a cortisone-like drug)
Cytosine arabinoside (Cytosar)
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 in dogs 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. Dogs generally do not experience the hair loss that affects humans undergoing chemotherapy. In fact, dogs 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.
Eighty to 90 percent of dogs treated for lymphosarcoma by chemotherapy achieve remission and average survival time is one year. Ten to 15 percent of dogs 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 experience 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. 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.
Treatment of one-half of the body has been used in dogs that have come out of remission. If a good response is obtained, the other half of the body is treated 3 to 4 weeks later. Adverse effects from this type of radiation therapy are similar to those observed after chemotherapy and include gastrointestinal symptoms and low white blood cell counts.
Radiation also 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 (i.e. to obtain biopsy specimens for examination by a veterinary pathologist).
Follow-up Care for Dogs with Lymphosarcoma (Lymphoma)
Promptly seek veterinary care if your dog develops signs of vague signs illness (loss of appetite, lethargy, unexplained weight loss) or abnormal swellings under the skin of the neck, shoulders, armpits or thighs.
Dogs with lymphosarcoma may have poor appetites due either to the cancer itself or the effects of chemotherapy. Dogs 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.
Dogs 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 dogs 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 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 dog’s white blood cell count during chemotherapy and may adjust drug dosage or schedule based on your pet’s white blood cell count.
Avoid exposure to the herbicide 2, 4-D which may increase the risk of developing lymphosarcoma. Other unknown environmental factors may increase the risk of lymphosarcoma but without knowledge of such factors exposure cannot be avoided.