It is not known why certain dogs develop lymphoma, and others do not. In some dogs, there is an underlying genetic component, and in others, there are no predisposing factors (most common). For cats, studies have shown that cats living in smoking households are 2.5 times more likely to develop lymphoma than cats living in nonsmoking households. Lymphoma usually arises in the lymphoid tissues of the body (lymph nodes, spleen, and bone marrow), although lymphoma can affect any part of the body. The most common presentation of lymphoma for dogs is enlargement of all of the lymph nodes that can be felt under the skin. The enlarged lymph nodes are usually not painful. Cats usually do not present with enlarged lymph nodes that you can feel. Often cats will have lymphoma in their gastrointestinal tract and will present to the veterinarian for vomiting, diarrhea, weight loss, or a decreased appetite. Cats and dogs can also have lymphoma in their thoracic (chest) cavity, and they may have difficulty breathing.
Blood samples (complete blood count and serum chemistry profile) and a urinalysis will be performed to determine your pet’s overall health status. Chest radiographs (x-rays), abdominal radiographs, and/or an abdominal ultrasound will be performed to look for involvement of certain organs with lymphoma. A fine needle aspirate may be performed of a lymph node to confirm the diagnosis of lymphoma. This is not painful for your pet. A bone marrow aspirate may also be performed looking for infiltration of lymphoma into the bone marrow. Your pet will be given an injection for pain before the procedure and will be under light anesthesia during the process. The procedure is usually performed from either the right or left front leg. Most dogs are not lame from the bone marrow aspirate, but your pet may be sleepy from the anesthesia, so it is important to keep them confined to a small area and avoid steps or walking the evening of the procedure. Occasionally, a biopsy of a lymph node is needed to confirm the diagnosis, and this is typically performed at the same time as the bone marrow aspirate.
Your pet’s oncologist will usually recommend that your pet be treated with systemic chemotherapy because lymphoma is always considered a systemic disease. Rarely would surgery and/or radiation therapy be utilized for lymphoma, but in certain cases, these modalities are recommended with concurrent chemotherapy. Occasionally, surgery is needed if the lymphoma is causing a blockage in the gastrointestinal tract. If surgery and/or radiation therapy are recommended, we will provide handouts to you and speak more about the specifics regarding these treatments.
Without any treatment, the average survival for dogs with lymphoma is 4 to 6 weeks. Approximately 50% of dogs with lymphoma will respond to prednisone (a steroid) alone, but the remission times are only 2 to 4 months with prednisone alone. Prednisone will cause your pet to urinate more, drink more, pant more, and may increase the appetite. Please be sure that he/she has free choice water at all times and goes outside frequently to urinate. Your pet may NOT receive any aspirin or aspirin like products such as Carprofen (Rimadyl®), Deracoxib (Deramaxx®), Etodolac (Etogesic®), Piroxicam (Feldane®), Tepoxalin (Zubrin®), or Meloxicam (Metacam®), while receiving prednisone, for the combination could cause a stomach ulcer. Most dogs will be weaned off the prednisone.
Most dogs and cats with lymphoma respond very well to chemotherapy and go into a state of remission. Approximately 10% of dogs with lymphoma are cured, so a “cure” is rare. Remission is defined as the disappearance of the signs and symptoms of lymphoma in response to treatment. Our goal with chemotherapy is to obtain a remission, meaning that the lymphoma is under control and not detectable, but the disease is still present.
In general, the remission time in cats is not as long as in dogs, but we certainly have had cats that do very well for quite some time. Prognosis is more difficult to determine for cats since the staging system and prognostic factors are not as well defined as they are for dogs. One important prognostic factor for cats is how well they respond to initial chemotherapy (if they go into a state of remission). The average remission times for cats with lymphoma with treatment are generally 7 to 9 months, but this varies tremendously from cat to cat.