Thanks to advances in veterinary medicine, nutrition and good daily care from owners like you, dogs and cats are living longer than ever before. But unfortunately, pets can be diagnosed with cancer, especially as grey creeps into the fur around their faces.
One of the most common cancers in both dogs and cats is lymphosarcoma, also known as lymphoma. As you might know, cancer occurs when there is uncontrolled division (and proliferation) of abnormal cells. In the case of lymphoma, a group of cells in the immune system called lymphocytes go haywire and continue to multiply.
Lymphoma can affect pets of any breed and any age, but it’s more frequently diagnosed in middle-aged and older pets.
Risk factors
No one is sure what, exactly, causes lymphoma in dogs and cats.
Since certain breeds, such as golden retrievers and Siamese cats, tend to be more affected than others, it’s possible there’s a genetic component.
In cats, infection with feline leukemia virus can lead to the development of lymphosarcoma, so outdoor cats can be at greater risk, especially if they aren’t vaccinated against feline leukemia.
Signs to watch for
Because lymphocytes can travel anywhere in the body, lymphoma may be widespread, or it can be localized to particular organs, including the gastrointestinal (GI) tract, spleen, liver, bone marrow, skin, central nervous system or other organs. As a result, the signs can vary, depending on what part of the body is affected. Some pets may just show general signs that they don’t feel well, such as lethargy and loss of appetite.
In dogs, it’s common to have one or more firm, swollen lymph nodes that can be seen or felt in locations such as the neck and behind the knee. The lymph nodes can enlarge quickly and potentially press against other body parts, compromising function. Lymph nodes in the neck, for example, can compress the trachea, making it difficult for the dog to breathe.
In cats, the GI system is most commonly affected. Signs of GI lymphoma in dogs and cats may include weight loss, lack of appetite, vomiting or diarrhea. Masses in the mediastinum, located between the lungs, may result in difficulty breathing or exercise intolerance.
Lymphoma diagnosis in pets
The diagnosis is usually made by taking a sample of the malignant cells, either through a fine-needle aspirate or a biopsy of an affected organ. By analyzing a biopsy sample, a specialist can determine whether the cancer is low, intermediate or high grade, depending on how rapidly the cells appear to be dividing. High-grade lymphoma is typically considered more malignant, but in some cases may be more responsive to treatment.
Other tests may be recommended such as blood tests (including feline leukemia testing in cats) and a urinalysis, to assess the pet’s overall health.
Once a diagnosis is made, lymphoma is typically classified by the anatomic area affected, type of lymphocyte (T-cell or B-cell) and by stages, to determine the extent of the disease, potential treatments and prognosis and to monitor response to therapy. Other tests may be needed, including a bone marrow biopsy, X-rays and an ultrasound.
The stages range from I to V, with a single lymph node involvement in stage I to bone marrow or other organ involvement in stage V. Each stage also has a substage, depending on whether the animal is showing signs of illness. Pets may progress from one stage to the next over time.
Prognosis and treatment
The prognosis for pets with lymphoma depends on a number of factors including overall health, stage of the disease and type of tumor.
Your veterinarian or a veterinary oncologist (a cancer specialist) can outline treatments that can help your pet feel more comfortable and potentially put the cancer in remission, although this is usually temporary.
Because lymphoma is generally considered a systemic disease, some type of chemotherapy is usually recommended. Pets typically tolerate chemotherapy fairly well, without as many side effects as humans. If the cancer is localized to a specific area, surgery or radiation therapy may be options. Your veterinarian can help you decide the right approach for you and your pet.
The information in this blog has been developed with our veterinarian and is designed to help educate pet parents. If you have questions or concerns about your pet's health or nutrition, please talk with your veterinarian.
