No two canine cancer patients look alike. Dogs can have benign tumours requiring only surgical removal for complete recovery. They can have devastating malignancies that have no known cure. Oncology is the branch of medicine dedicated to the study of cancer. Veterinary medicine is making new advances in the diagnosis and treatment of cancer in pets. Lymphosarcoma (lymphoma, LSA) and osteosarcoma (OSA) are two cancers commonly seen in dogs.
Lymphosarcoma
Lymphocytes are white blood cells which normally play a vital role in the immune system and fighting infection. Lymphosarcoma or lymphoma refers to a type of tumour where lymphocytes proliferate in a cancerous manner. These abnormal cells may invade anywhere in the body but are typically found in lymph nodes, the spleen, the liver, the gastrointestinal system, or the skin. Many dogs are initially brought into the veterinarian for swelling of the lymph nodes in the neck area. These swellings are generally non-painful and patients may not show any other signs of illness in the early stages.
Lymphosarcoma is not considered to spread or metastasize because the lymphocytes are normally present in virtually all organs of the body. A patient’s prognosis and treatment plan is based on the stage of LSA as assessed by physical examination, blood tests, lymph node aspirate or biopsy, x-rays, ultrasound, and bone marrow aspirate. Special tests can be performed to determine whether B-cell lymphocytes or T-cell lymphocytes are the predominate cell-type present. B-cell forms may have a better prognosis, although treatment protocols are similar.
Staging of Lymphosarcoma
Stage I: single lymph node enlarged
Stage II: multiple nodes enlarged on either the front half or back half of the body
Stage III: multiple nodes enlarged on both front and back halves of body
Stage IV: involvement of the liver and/or spleen
Stage V: bone marrow involvement, or involvement of other organs (e.g. gastrointestinal, skin, nervous system)
Each numbered stage can be further divided into substages, of which there are two: A and B. Patients with substage A feel well while patients with substage B are ill.
Chemotherapy
Chemotherapy is the mainstay of treatment for lymphosarcoma. Some protocols use several medications scheduled over a number weeks while other protocols use a single agent over a specific time period. A veterinarian will decide which protocol to use in an individual patient based on the wellness of the dog at the start of the treatment, actual staging, the pet parent’s own philosophy about therapy and cost. Chemotherapy drugs can be expensive, and protocols require patients to be hospitalized for IVs and monitoring-just like in people.
The goal of chemotherapy in dogs is somewhat different than the goal in people. We want our pets to have a reduction in clinical symptoms in order to have an improved quality of life and, hopefully, have the disease go into remission. Veterinarians use lower doses of chemotherapy in our patients, and so fewer dogs will show significant or lasting side effects. Lymphosarcoma is generally not considered a curable disease in canine patients, but most dogs will have initial remission times of 6-9 months. With subsequent chemotherapy, we expect the remission times to be shorter. Many dogs will survive over 12 months.
Osteosarcoma
Osteosarcoma is the most common primary bone tumour in dogs causing approximately 85% of tumours in the skeleton. There is an old adage that suggests these tumours occur away from the elbow and toward the knee, but OSA can occur in any bone. Osteosarcoma is usually seen in mature adult or elderly dogs, but the large and giant-breeds may tend to develop tumours at younger ages.
The tumour arises deep in the affected bone and progressively destroys the normal bone from the inside out. As the tumour grows, the area becomes painful. In older dogs, OSA may be mistaken for arthritis in the early stages. Over a few months, these dogs become more lame due to microscopic fractures in the bone and swelling of tissue. Depending on the location of the tumour, a swelling or lump may be seen in affected leg. In certain forms of OSA, the lameness appears to occur quite suddenly, possibly because of fractures associated with the weakened bone. Any change in gait or pain associated with the limbs in large or giant-breed dogs that does not resolve with symptomatic treatment needs to be investigated by your veterinarian.
Osteosarcoma is known to spread or metastasize to other organs, often the lungs, in the majority of dogs. Most dogs (over 90%) are considered to have metastasis at the time of diagnosis even when the signs are not clinically apparent. Osteosarcoma is diagnosed based on clinical examination, x-rays, blood tests, and lymph node sampling.
Treatment
When we treat OSA, veterinarians looking to improve the quality of life (relieve pain) and increase lifespan. Amputation to remove the primary tumour and chemotherapy to control the metastatic disease are the best options to achieve these goals. While the prospect of amputation can be quite difficult for a pet parent, most dogs without problems like arthritis do very well. Limb sparing treatments can be considered when the tumour is located near the wrist. Palliative treatments with pain relief medications, drugs aimed at slowing down bone break down, and even radiation therapy are available to the veterinary patient. Gene-therapy trials suggest future promise in OSA treatment. Veterinarians and pet parents need to establish a frank dialogue about the prognosis for quality of life and lifespan, potential complications, and costs of therapy to ensure that the therapeutic plan takes into account the best interests of the dog.
The prognosis for dogs treated with amputation or limb-sparing surgery and treated with chemotherapy is fair to good. Approximately 50% of dogs will be alive at one year after diagnosis; approximately 25% of dogs will be alive two years after diagnosis, and occasionally dogs will be cured. Dogs treated with amputation alone have an average lifespan of 6 months before complications of the local tumour or metastatic disease are fatal or result in euthanasia.
Cancer is one of the leading causes of death among mature pets. Tumours may affect any part of the body, and regular physical examinations by your veterinarian are the key to early intervention in the diagnosis and treatment of cancer. Please remember that while statistics in the above article may be useful, they will not be able to predict how an individual patient will respond to any specific therapeutic regimen.
Help Petsecure ‘FURther the Fight’. For every new Facebook friend or Twitter follower, Petsecure will donate $1. to the Ontario Vet College Pet Trust Fund towards pet cancer research.
For more information about pet cancer, visit: www.petsecure.com/pcam
Dr. Colleen Skavinsky,Chief Veterinary Officer