Feline Lymphosarcoma (Lymphoma, LSA)
Lymphosarcoma is a tumor caused by a cancerous proliferation of lymphocytes or, cells that normally function in the immune system. This is a very common tumor in cats and can present in a variety of ways. At one time, feline leukemia virus (FeLV) was a leading cause of LSA in cats and typically young cats were infected. Now that the incidence of FeLV has decreased cats still develop LSA but it is generally older cats and different forms. The Feline aids virus (FIV) has also been shown to increase the risk of a cat developing LSA six times over a non-infected cat. Any breed of cat can develop LSA. The cause of the disease unrelated to FeLV or FIV is unknown although environmental smoke exposure has been found to increase a cat’s risk of LSA, and a possible link to long standing inflammatory disease has long been theorized.
What you might see/ Clinical presentation
Cats with LSA present with a variety of signs because lymphocytes can be found in nearly every organ in the body. Also, cats seem to have more forms of LSA in atypical locations or not in normal lymphoid tissues, as compared to other species. Most species including man present with large lymph nodes, but this is a rare form of LSA in cats. Young cats typically present for masses in the chest cavity and owners notice signs of difficulties breathing or vomiting of food. Older cats develop the tumor in their intestines quite commonly and owners may notice signs such as weight loss, diarrhea or vomiting. They also can however develop LSA in areas as diverse as the nasal passages, kidneys, spinal cord, liver, eyes, or a single lymph node, and the signs seen will be more specific for the organ affected. Because cats present with such a variety of organs affected there is no valid staging system for feline LSA and a cat diagnosed with the disease will more likely be staged by the organ affected (eg. gastrointestinal LSA, mediastinal LSA etc.)
Biological behavior of LSA
Even though many cats present with only a single site of involvement, LSA is viewed as a systemic disease. Lymphocytes in their normal functioning capacity travel throughout the body and as a cancer the disease is also moving though not in a classical sense "metastasizing". Even if a tumor diagnosed as LSA has been surgically removed the disease is not gone.
Clinical staging (determination of the extent of the tumor)
Because of the organs that LSA commonly involves, staging a cat with a LSA can involve aspiration of one or more lymph nodes or masses, thoracic radiographs abdominal radiographs or ultrasound (to look for big nodes in the abdomen and to look at the liver and spleen), or bone marrow examination. Obtaining blood for a complete blood count and biochemical profile, FeLV, FIV, and a urinalysis is always advised as these can help assess overall health and provide information that potentially influences treatment recommendations. Sometimes, special stains to determine if the LSA is of B-cell or T-cell origin (B-cells and T-cells are specific types of lymphocytes) are recommended because of prognostic significance, although treatment recommendations may be the same for either type. Staging the disease can be critical in choosing treatment protocols.
Chemotherapy should always be considered a critical part of the treatment for LSA. The best responses in terms of length of tumor control and survival are generally seen with protocols that entail administration of more than one chemotherapy drug, although there are approaches that involve administration of a single drug. Chemotherapy drugs commonly used include: doxorubicin, vincristine, cyclophosphamide, prednisone, and L-Aspariginase, but many others are also used. Some protocols are very aggressive and relatively short (six month total) and others are less aggressive but extend for one to two years. The decision of which protocol is to be used does depend on the results of the tumor biopsy (not all LSA is the same) and the staging results. Thankfully, the chemotherapy generally act quickly so that even cats with sever signs can have relief fairly soon after starting therapy (sometimes as quickly as 24 hours). Surgery is sometimes recommended as a part of the treatment but this is usually either to reach a diagnosis or to remove a potentially life threatening problem (for example intestinal rupture due to a tumor mass). Surgery is never curative and should always be followed by chemotherapy to best extend the cat’s life. Radiation can also play a role in the treatment of very localized LSA. The primary site most benefiting from radiation therapy is nasal LSA.
Cats with LSA have unpredictable responses and survivals. Depending on the site of the tumor, mean survivals with chemotherapy range from 6-9 months. The problem is that this is only an average and most cats tend to do either much worse or much better. Young cats, FeLV negative, with mediastinal LSA are quite regularly cured with chemotherapy; cats with LSA in their central nervous system typically have a bad prognosis, but most other forms of LSA in cats have unpredictable outcomes. Generally it is best to at least try a chemotherapy protocol because it may be the only way to see how an individual cat will do. Cats often do not enjoy receiving chemotherapy, but veterinary oncologist try hard to make the regime tolerable for each feline patient even if it means modifications in a protocol.
Future treatment options
New protocols are tried in feline lymphoma but results have been similar with each drug regime investigated. Most likely our survivals will always be similar until we either accept greater toxicity (meaning most cats will be very sick from the treatment and some may even die), or a completely novel treatment is invented. Using half or whole body radiation therapy may prove helpful. The development an antibody specific for cat lymphoma, which could recognize all cat lymphomas and yet no normal lymphocytes, and be attached to a toxin or other cell killing mechanism, is a far off dream.
LSA is one of the most chemotherapy-responsive tumors seen in veterinary medicine and cats can tolerate chemotherapy relatively well, or protocols can be modified so that an individual cat can maintain a good quality of life while on chemotherapy. Unfortunately we have few strong predictors of which cats will have good responses to chemotherapy and long survivals, and survival is therefore difficult to estimate at the outset. Often the only way to know how a cat will respond to treatment, is to start treatment.