Lymphoma is a cancer of the lymphocyte, which is a type of white blood cell that helps deal with inflammation and infection in your pet’s body.

If left untreated most dogs will only have one to two months until they are very sick from their disease and most will die within 4 months of diagnosis.

Chemotherapy is the mainstay of treatment for lymphosarcoma.

Lymphosarcoma is very sensitive to chemotherapy and up to 90% of dogs treated with a multi-drug protocol will go into remission, with average survival times of about 12-18 months depending on the plan used.  Approximately 20 -25% of dogs live 2 years or longer after initiation of chemotherapy.  

Most dogs tolerate chemotherapy very well and have minimal to no side effects. Serious side effects are only seen in about 5-10% of patients treated.

What is Lymphosarcoma?

• Lymphoma is a cancer of the lymphocyte (see photo right of malignant lymphocytes), which is a type of white blood cell that helps deal with inflammation and infection in your pet’s body.
  
• Lymphoma typically develops in organs with a large amount of lymphoid tissue, such as the lymph nodes, spleen, liver, gastrointestinal tract and bone marrow. However, it may arise in almost any tissue in the body.3
  
• The average age of dogs with lymphosarcoma is between six to nine years, although dogs of any age can be affected.4,5  Certain breeds have been reported to have a higher incidence of lymphoma such as Boxers, Bull Mastiffs, Basset Hounds, Saint Bernards, Scottish terriers, Airedales and Bulldogs.6,7  Breeds with a lower risk include Dachshunds and Pomeranians.6,7  Recent evidence has also shown a high incidence in Golden and Labrador Retrievers.
  
• The cause of lymphoma is dogs is ultimately unknown and likely involves a number of factors.3  In general, all tumors arise from an underlying abnormality in DNA or the immune system.

Types of Lymphosarcoma & Symptoms

• Lymphoma can be divided into five different forms depending on the predominant site of the tumor.
  
  1. Multi-centric: Eighty percent of dogs with lymphoma develop the multi-centric form.8  Multi-centric means that many different organs are involved. This is the most common form and typically presents as enlargement of one or more external lymph nodes. The most commonly affected external lymph nodes are the ones under the chin (submandibular), in front of the shoulders (pre-scapular), in the groin (inguinal) and behind the knees (popliteal). Most pets do not feel sick and just have enlarged lymph nodes. Some have only very mild signs such as lethargy or decreased appetite, while others can show more severe signs such as weight loss, vomiting, diarrhea, excessive thirst or urination, extreme weakness or difficulty breathing. The severity of the signs depends on the extent of the tumor and on whether the cancer has caused changes in organ function. Other organs, such as the liver, spleen and bone marrow can be involved as well.
     
  2. Gastrointestinal Tract:  Five to seven percent of dogs develop the gastrointestinal form.8  Dogs with this form of lymphoma may show signs of weight loss, decreased appetite, vomiting, diarrhea and low protein levels.9,10      
     
  3. Mediastinal:  Approximately five percent of dogs develop this form of lymphoma.8  The mediastinum is a term used to describe the area that separates both halves of the chest and includes organs such as lymph nodes, esophagus, trachea and heart. It is specific enlargement and involvement of the lymph nodes in the mediastinum. Dogs with this form may show signs of a cough, difficulty breathing or excessive thirst and urination due to an elevated calcium level.
     
  4. Skin:  Another term for skin lymphoma is cutaneous lymphoma. Dogs with cutaneous lymphoma can present with relatively mild signs of itchy, flaky, scaly, reddened skin or they can have more severe signs of ulcerated skin lumps that are uncomfortable. The footpads and gums are frequently affected and other organs such as the spleen, liver, lymph nodes and bone marrow can eventually become affected.
     
  5. Bone Marrow:  Occasionally lymphoma cells may infiltrate the bone marrow. Clinical signs in these dogs are usually related to decreases in the numbers of normal bone marrow cells, such as red blood cells (which carry oxygen to tissues), white blood cells (which fight infection) and platelets (which help with clotting). Extreme lethargy secondary to anemia (decreased red blood cell level), sepsis (systemic bacterial infection) and bleeding are relatively common problems.

Diagnosis

• Fine needle aspiration—where we insert a needle into a lymph node, draw some cells out, spread them on a slide and have the pathologist observe them under a microscope—is often enough to get a definitive diagnosis of lymphosarcoma.
  
• Occasionally a biopsy where a small piece of tissue is taken from the lymph node under heavy sedation or full anesthesia is required. Rarely other more advanced diagnostics are required.
  
• A complete evaluation of your pet’s general health, as well as tests to determine his/her stage will include a complete blood count (CBC), chemistry panel, urinalysis, x-rays of the abdomen, x-rays of the chest, a bone marrow aspirate and a test for B-cells vs. T-cells.
  
• Occasionally an ultrasound of the abdomen is recommended because ultrasound allows us to look “inside” the organs unlike x-rays.
  
• A CBC, chemistry panel and urinalysis may show important information regarding the effects of the cancer on body functions and your pet’s ability to handle chemotherapy.
  
• X-rays of the abdomen are to determine if the liver and/or spleen are enlarged, as well as if there are any enlarged lymph nodes in the abdomen. X-rays of the chest are to evaluate the heart and lungs, as well as to determine if there are any enlarged lymph nodes in the chest.
  
• A bone marrow aspirate is to determine if there is bone marrow involvement and is very important for treatment and prognostic information. Bone marrow aspirates are very well tolerated with mild sedation. A needle is inserted in the shoulder region and a very small amount of bone marrow is withdrawn. Rarely do we have to use the hip to get a better sample. It is extremely rare for an animal to become lame or excessively painful after a bone marrow aspirate.
  
• There are two different types of lymphocytes in the body, B-cells and T-cells. The test to determine which one makes up your pet’s lymphosarcoma is called immunophenotyping and can be performed on the sample obtained by fine needle aspiration.
• There are five stages of multi-centric lymphosarcoma:
  1. Involvement of only one lymph node (rare).
     
  2. Involvement of a set of lymph nodes in one general area and on one side of the diaphragm (rare).
     
  3. Involvement of all lymph nodes on the outside of the body and on both sides of the diaphragm (common).
     
  4. Spleen and/or liver involvement (common).
     
  5. Bone marrow, brain, eye and/or spinal cord involvement (rare).
  6. Sub stages:
     
  • Sub-stage a – feeling well or only has very mild signs.
    
  • Sub-stage b – significant symptoms (vomiting, diarrhea, lethargy, decreased appetite).

Treatment and Prognosis

• If left untreated most dogs will only have one to two months until they are very sick from their disease and most will die within 4 months of diagnosis.11
  
• Chemotherapy is the mainstay of treatment for lymphosarcoma.  Lymphosarcoma is very sensitive to chemotherapy and up to 90% of dogs treated with a multi-drug protocol will go into remission, with average survival times of about 12-18 months depending on the plan used.3  Approximately 20 -25% of dogs live 2 years or longer after initiation of chemotherapy.3  
  
• The definition of remission is the complete disappearance of detectable cancer. A remission is not a cure, but it does allow your pet to experience a good quality of life. This is important to remember because chemotherapy should not be discontinued when a remission is achieved. The length of remission depends upon many factors including the length of therapy, the primary site, stage and how sick your pet is at the start of therapy.
  
• The exact drugs and treatment schedule will depend upon how aggressively the cancer is behaving, how sick your pet is at the start of therapy and if there are any abnormalities in organ function, such as liver and kidney function. Factors that influence the outcome of treatment include location of the tumor, aggressiveness of the tumor, whether or not a pet is sick from their disease (sick patients do not do as well), whether or not there is bone marrow involvement (stage five is worse), whether or not there is a high blood calcium lever (high calcium levels are worse) and the immunophenotype (B-cell lymphosarcoma does better).3  
  
• In a typical multi-drug protocol, four to five different chemotherapy drugs are alternated in order to reduce the chance that the tumor cells will become resistant and to reduce the risk of side effects. These drugs include Elspar (L-asparaginase), vincristine, Adriamycin (doxorubicin), Cytoxan (cyclophosphamide) and prednisone.
  
• Initially, treatments are given frequently (i.e. once weekly) but depending upon the response and specific protocol, treatments are then spread out and /or discontinued. We use two types of multi-drug plans—a short-term and a long-term plan. Short term plans are 25 weeks in length and are used for “average” dogs with lymphosarcoma. Short term plans have several advantages including fewer treatments, lower cost and possibly fewer problems with resistance to chemotherapy. Long term plans are 52 weeks in length and are used for pets with advanced stage disease that are less likely to do well.
  
• There are other chemotherapy options besides a multi-drug plan, including prednisone alone, single agent chemotherapy or other combination plans. Prednisone alone will result in a short-lived remission of approximately one to two months.3  Long-term prednisone use alone may lead to resistance of other chemotherapy drugs. Adriamycin (doxorubicin) is the most effective chemotherapy drug available for lymphosarcoma and when used alone approximately 50-75% of patients will respond with a median survival time of six to eight months.12,13,14,15  
  
• If a patient comes out of remission, we can try to put them back into remission using either the same plan (depending on how they did with it the first time) or a different plan. This is called a “rescue.” Unfortunately, the chances of obtaining a second remission are lower and the risk of side effect may be higher. There are many dogs, however, that respond well to “rescue” plans and can survive a significantly longer period of time.

Potential Side Effects

• Most dogs tolerate chemotherapy very well and have minimal to no side effects. Serious side effects are only seen in about 5-10% of patients treated.
  
• Dogs do not go completely bald with chemotherapy. Increased shedding and some fur and whisker loss are common in most breeds. Dog breeds that have fur that grows similar to a human’s hair (i.e. Poodles, Terriers, and Old English sheepdogs) may develop bald patches, but rarely lose all of their fur. Fur may grow back slowly after being clipped as well. Fur growth goes back to normal once your pet finishes chemotherapy, but it may vary in color and texture.
  
• Mild decreased appetite, vomiting, diarrhea and lethargy may occur about three to four days after chemotherapy, which are easily treated with oral medications.
  
• Decreases in white blood cell levels and platelets are possible about seven to 10 days after chemotherapy. These changes rarely cause a clinical problem for your pet, however, some dogs are lethargic if they have a low white blood cell level and are predisposed to a systemic infection (sepsis).
• Sepsis is life threatening and those patients that develop an infection with a low white blood cell level must be admitted to the hospital for supportive care with intravenous fluids and antibiotics. Sepsis secondary to chemotherapy is extremely rare even in dogs that have a low white blood cell count.   
      
  * references are available upon request