Lymphoma is a cancer that arises from the unchecked proliferation of lymphocytes, a type of white blood cell that circulates in the blood and functions as part of the immune system. Lymphoma -- also referred to as lymphosarcoma or LSA -- is considered relatively common in dogs and very common in cats.
Though lymphoma often presents initially as a swelling of the lymph nodes (in dogs, in particular) and can affect specific organs (spleen, kidney, liver, skin, intestines, and bone marrow, among others), it is considered a systemic disease.
In dogs, lymphoma is one of the few cancers that strikes young to middle-aged dogs preferentially. By contrast, feline lymphoma is seen in all ages of cats.
As certain breeds of dogs are overrepresented among lymphoma patients, a genetic origin for this disease can be inferred for the canine version of this disease. The exact method of inheritance, however, is not known. No genetic predisposition had been identified for lymphoma in cats.
In dogs, it is impossible to pinpoint the exact cause of lymphoma. A combination of genetic and environmental factors is assumed.
In cats, however, we know that lymphoma can come about as the result of the feline leukemia virus. Its incidence has also been found to be six times higher in cats infected with the feline aids virus (FIV). Recent studies have further demonstrated that cats who are chronically exposed to second-hand tobacco smoke and suffer from chronic inflammatory diseases are more likely to develop lymphoma later in life.
Unfortunately, the prognosis for all lymphoma patients is poor unless treatment is elected. In the absence of treatment with chemotherapy and/or another combination of palliative drugs, most pets will succumb to lymphoma within weeks of its presentation. Luckily, lymphoma is considered highly treatable with chemotherapy.
Yet even with the successful use of chemotherapy (commonly employed in dogs and highly recommended for both dogs and cats), survival times average only sixteen months for dogs. In cats, however, survival times following chemotherapy can vary widely. While some may respond very poorly to treatment, other feline lymphoma patients can even be cured via chemotherapy.
Symptoms and Identification
As a systemic disease, lymphoma can present in any number of ways:In dogs, enlarged lymph nodes, lethargy, poor appetite, fever, vomiting, and general malaise is typically observed.Because lymphoma affects cats in a variety of organs, symptoms will vary depending on the systems involved. Affected systems have been found to vary according to age. Younger cats more often present with respiratory symptoms consistent with the growth of masses in the chest. Older cats are more likely to develop lymphoma tumors in their intestines. Weight loss, diarrhea, and vomiting are more typical in these latter cases.
Cats can also develop lymphoma in atypical sites like the nasal passages, kidneys, spinal cord, liver, eyes, or even in one single lymph node. Symptoms will vary depending on the organ(s) affected.
The following tests are strongly recommended in the course of lymphoma diagnosis:
Complete blood count (CBC)
Blood biochemistry panel
Feline leukemia and Feline aids testing (for cats)
Chest and abdominal X-rays
Fine needle aspirate of the lymph nodes and/or affected organs
Bone marrow analysis
In dogs, lymph node aspirates can be evaluated for cytology, PCR, and/or flow cytometry to arrive at a definitive diagnosis and help determine the stage of the disease.
Since cats don't tend to present with enlarged lymph nodes, similar evaluation of any abdominal or thoracic fluid -- along with fine needle aspirate or biopsy of the affected organs -- is recommended, instead.
Analysis of the bone marrow may also be undertaken to stage the disease's progress and help direct treatment.
Lymphoma can affect any breed of dog but Golden Retrievers are overrepresented among lymphoma patients. The Boxer, Scottish Terrier, Basset Hound, Airedale Terrier, Chow Chow, German Shepherd, Poodle, St. Bernard, Bulldog, Beagle, and Rottweiler are also at higher risk of developing lymphoma.
Cats of any breed can be affected. No genetic predisposition has been identified among felines.
Because lymphoma is a systemic disease, the best approach to treatment necessarily involves the use of systemic chemotherapy drugs. A variety of drug combinations (referred to as "protocols") are available for dogs and cats who suffer from this disease. All are designed to prolong comfortable life -- not to cure the disease -- and, as such, relatively small doses are employed so that noxious side effects are minimized.
In most canine cases (between 75% to 90%, depending on the protocol employed), complete remission is achieved. The average patient enjoys a good to excellent quality of life for sixteen months before experiencing a relapse. Some lucky dogs may even respond positively to a second round of chemotherapy.
While a complete cure for lymphoma is considered highly elusive in the case of afflicted dogs (especially given veterinary medicine's relatively non-aggressive approach to chemotherapy), several experimental approaches have been shown to extend remission duration in dogs -- dramatically in some cases. The most common of these involves whole body irradiation and bone marrow transplantation.
Though cats' median survival times after chemotherapy are lower (6 to 9 months), there's a wide range of responses to treatment. Indeed, some cats can be completely cured after chemotherapy. This is especially true for otherwise healthy young cats who experience a form of lymphoma that affects their chest (mediastinal).
While less commonly employed, surgery and radiation can also be helpful as an adjunct to chemotherapy. Surgery is most often recommended only when absolutely necessary, as when a mass in the intestines leads to a rupture. Meanwhile, radiation is employed only when a very localized lesion presents itself, as in the less typical case of nasal lymphoma in cats.
It is strongly recommended that owners who hope to gain most comfortable longevity on behalf of their pets consult a board-certified oncologist to receive the fullest understanding of the broad range of their pet's treatment options.
As with many cancers that require chemotherapy and an oncologist's assistance for best outcomes, the cost of this disease can be prohibitive. Pets who suffer from these tumors may experience treatment costs that extend well beyond the $10,000 mark, especially should owners elect to explore all available treatment options.
The cost of definitive diagnosis is typically around $500, but increases dramatically when the patient's cancer is thoroughly investigated and staged. It's not unusual for owners to spend several thousand dollars in this process.
The cost of chemotherapy in these cases varies widely depending on the protocol elected and the patient's size. The cost of surgery itself will depend on the surgeon's degree of specialization along with the anatomical location of the tumor, but $1,000 to $3,000 is typical. Radiation therapy in nasal cases tends to cost anywhere between $5,000 and $10,000. Some of the newer experimental approaches may be had for $15,000 or less, but these are largely unavailable except in veterinary school type settings.
It cannot be overstated that the cost of diagnosis and treatment depends on many factors including geographic location (cost of living), standard of care (lower vs. higher standards of veterinary care), whether specialty hospitals are employed (higher quality equipment, certified personnel, and board-certification for veterinarians specialized in oncology).
Unfortunately, many owners elect not to treat their pets due to the extreme expenses often associated with lymphoma.
As with most cancers, prevention of lymphoma is a complex issue:
In dogs there is no known approach to lymphoma prevention.
In cats, limiting exposure to feline leukemia - FIV-positive - cats and vaccinating at-risk cats against feline leukemia is the only accepted approach to prevention of lymphoma. Limiting exposure to second-hand tobacco smoke is doubtless of some benefit as well.
Ettinger, Stephen J. Feldman, Edward C. (1995). Textbook of Veterinary Internal Medicine (4th ed.). W.B. Saunders Company. ISBN 0-7216-6795-3.
Kaneene J, Miller R (1999). "Re-analysis of 2,4-D use and the occurrence of canine malignant lymphoma". Vet Hum Toxicol 41 (3): 164-70. PMID 10349709.
Modiano J, Breen M, Burnett R, Parker H, Inusah S, Thomas R, Avery P, Lindblad-Toh K, Ostrander E, Cutter G, Avery A (2005). "Distinct B-cell and T-cell lymphoproliferative disease prevalence among dog breeds indicates heritable risk". Cancer Res 65 (13): 5654-61. doi:10.1158/0008-5472.CAN-04-4613. PMID 15994938.
Morrison, Wallace B. (1998). Cancer in Dogs and Cats (1st ed.). Williams and Wilkins. ISBN 0-683-06105-4.
Seo K, Choi U, Bae B, Park M, Hwang C, Kim D, Youn H (2006). "Mediastinal lymphoma in a young Turkish Angora cat". J Vet Sci 7 (2): 199-201. PMID 16645348.
Richter, Keith P. (2006). "Feline gastrointestinal lymphoma". Proceedings of the North American Veterinary Conference. Retrieved 2007-01-28.
Canine Malignant Lymphoma: Introduction". The Merck Veterinary Manual. 2006. Retrieved 2007-01-28.Williams LE, Johnson JL, Hauck ML, et al. Chemotherapy followed by half- body radiation therapy for canine lymphoma. J Vet Intern Med 2004;18(5):703- 709.
"Feline Leukemia Virus and Related Diseases: Introduction". The Merck Veterinary Manual. 2006. Retrieved 2007-01-28.