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What is lymphosarcoma?
Lymphosarcoma (lymphoma) is a cancer of lymphocytes (a type of blood cell) and lymphoid tissues. Lymphoid tissue is present in many places in the body including lymph nodes, spleen, liver, gastrointestinal tract and bone marrow. In most cases, veterinarians cannot determine the cause of lymphosarcoma.
Are certain breeds or ages more susceptible?
Lymphosarcoma is the third most common cancer in dogs most commonly affecting 6 to 9-year old dogs (although any age can be affected). Males and females are equally at risk.
The following breeds may be more likely to develop this type of cancer: Boxer, German Shepherd, Golden Retriever, Scotties, Westies, and Pointers.
Types and symptoms of lymphosarcoma
Lymphosarcoma takes five different forms, depending on the primary site of the tumor.
• External lymph nodes : The most common form involves the external lymph nodes and the symptoms vary. Some dogs may not feel sick or may exhibit only mild signs like fatigue or decreased appetite. Other dogs may have more severe signs such as weight loss, vomiting, diarrhea, excessive thirst or urination, weakness or difficulty breathing. The severity depends upon the extent of the tumor and on whether the cancer has caused changes in organ function. In many cases, the only noticeable sign is an enlargement of the lymph nodes under the neck, behind the knees or in front of the shoulders. Other organs, such as the liver, spleen and bone marrow can be involved as well.
• Gastrointestinal tract : Dogs with this type of lymphosarcoma may exhibit vomiting, diarrhea, weight loss or a decreased appetite.
• Mediastinal : The mediastinum is a term used for a special aggregation of lymphoid tissue in the chest. Dogs with this type often have difficulty breathing or exhibit excessive urination/thirst.
• Skin: Known as cutaneous lymphosarcoma, the symptoms include flaky, scaly, reddened, and/or itchy skin. Dogs may also have lumps in the skin, which can ulcerate. The footpads and gums may also be involved. Other organs such as lymph nodes, liver, spleen and bone marrow are variably involved.
• Bone marrow : This type is referred to as leukemia. The signs are usually related to decreased numbers of normal blood cells which are made in the bone marrow. Anemia, infections and bleeding are common problems.
What happens if my dog is suspected to have lymphosarcoma?
First, the doctor will obtain a biopsy or aspirate of the affected tissues and then search for tumors in other locations. A complete blood count (CBC), a serum chemistry profile and urinalysis are also performed as they provide important information regarding the effects of the cancer as well as the patient's ability to handle chemotherapy. Then, the doctor will take a series of x-rays, allowing him/her to search the body for additional tumors. Abdominal x-rays and/or ultrasound are used to evaluate the liver, spleen, internal lymph nodes and intestinal tract. Chest x-rays help spot enlarged internal lymph nodes, lung involvement or an enlarged mediastinum. Finally, the doctor takes a bone marrow aspirate.
Treatment and prognosis
Lymphosarcoma is very sensitive to chemotherapy making it the main treatment method. With chemotherapy, 85% of dogs will go into remission. Remission is not a cure, but is defined as the complete disappearance of detectable cancer allowing the pet a good quality of life. It is important to note that chemotherapy should not discontinue with remission. The length of remission depends upon many factors including the primary tumor site, how sick an animal is at the start of treatment and the extent of disease. For dogs with the most common type (external lymph nodes enlargement), the average remission time is usually around eight to ten months with overall survival time of approximately one year.
The exact treatment depends on the aggressiveness of the cancer, the dog's health at the start of treatment and organ function (i.e. changes in liver and kidney function). Typically, a treatment will involved the alternation of four to eight chemotherapy drugs. The change reduces both the chance that the tumor cells will become resistant and side effects. Initially, treatments are given frequently (i.e. once per week) but depending upon the response, treatments are then spread out and/or discontinued. About 10-15% of dogs will live longer than 2 years.
Most dogs handle chemotherapy well and have minimal side effects. Serious side effects are only seen in 5-10% of the patients treated. These include nausea, vomiting, and loss of appetite, diarrhea, extreme tiredness or infection. Hair loss or slow hair growth may also occur in certain instances.
Source: New England Veterinary Oncology Group, LLP