Lymphoma is the most common cancer in cats, and many cat owners have experienced the pain of a diagnosis of lymphoma in their companions. Because lymphoma is so common, many people have questions about it. What causes it? How is it diagnosed? Can it be treated?
In fact, lymphoma is not a single disease. It is a description that applies to a number of types of cancer. All forms of lymphoma are cancers of the immune system, and involve cells of the lymphatic system. The immune system exists throughout the body, and lymphoma can therefore manifest in many different ways. The symptoms and prognosis for cats with lymphoma depend upon the organ or organs affected, and on the aggressiveness of the underlying cancer.
In dogs, palpably swollen lymph nodes are the most common symptom of lymphoma. Such palpable lumps do not occur as commonly in cats with lymphoma. Instead, lymphoma generally manifests with more subtle symptoms.
One of the most common forms of lymphoma in cats is intestinal lymphoma. In this condition, the intestines become infiltrated with cancerous lymphatic cells. Poor appetite, weight loss, vomiting, and diarrhea may occur. The intestines may become palpably thickened. In some instances, lymph nodes adjacent to the intestines will become markedly enlarged, leading to an intra-abdominal mass that can be palpated by veterinarians.
There are several different types of intestinal lymphoma, and they vary in their aggressiveness. However, one of the most common types appears to occur as a complication of inflammatory bowel disease. This type of lymphoma generally is relatively slowly progressive; it therefore carries a better prognosis than many other types of cancer.
Because the immune system exists almost everywhere in the body, lymphoma can occur in just about any organ. Cats may experience lymphoma of the nose, which can cause sinus congestion, nasal discharge, sneezing, and difficulty breathing. Lymphoma can occur in the chest, causing coughing and labored breath. Lymphoma can infiltrate the eyes, compromising vision. Lymphoma can occur in the kidneys, causing kidney failure (however, lymphoma is not the most common form of kidney disease in cats). Lymphoma has been documented to occur in the skin, causing rashes and other cutaneous irregularities.
The cause (or, more properly, causes) of lymphoma has not been definitively determined, but there appear to be multiple risk factors for the various forms of lymphoma. Inflammatory bowel disease already has been mentioned as a risk factor for intestinal lymphoma. Feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) also are known risk factors. However, most cases of lymphoma occur in cats who are not affected by either virus. It is likely that hereditary factors play a major role in most cases. Exposure to carcinogens likely contributes to some forms of lymphoma.
Lymphoma, like most cancers, is more common in older cats. However, there unfortunately are forms of lymphoma that strike young individuals as well.
Lymphoma is most commonly diagnosed through tissue samples. In some instances, biopsies are taken of suspicious sites; biopsies of the nose and intestines are often accomplished through endoscopy. Biopsies involve removal of small pieces of tissue for analysis by pathologists. In other instances, ultrasound may utilized to guide needles into the spleen, liver, or intra-abdominal lymph nodes. This technique, called aspiration, is similar to biopsy but is less invasive. Blood and urine tests rarely can reveal lymphoma; however, most cats with lymphoma undergo such testing, as well as radiography (X-rays), to rule out other diseases.
Lymphoma is a malignant disease process, and I am always saddened when I diagnose it. However, owners of cats with lymphoma should take solace in the fact that many forms of lymphoma respond well to treatment.
In humans, lymphoma was formerly one of the deadliest cancers. Over the past 20 years, significant improvements in treatment have rendered it one of the most survivable cancers. Veterinary medicine has piggybacked on some of the advances in human medicine.
Most forms of lymphoma are treated with chemotherapy. Although many people cringe at the thought of chemo, be aware that cats generally tolerate chemotherapy much better than humans. In fact, many cats experience few to no chemo side effects. Recent advances in the understanding of lymphoma have enabled veterinary oncologists to type each cat’s disease, and then tailor chemotherapy protocols to the individual situation.
It is possible for many cats with lymphoma to go into complete remission. I have known many cats who enjoyed remission (disease free) periods of several years.
Such favorable outcomes are not universal, but they are sufficiently common that I always recommend that owners of cats with lymphoma see a veterinary oncologist. Lymphoma is common and, if not treated, deadly condition. However, for cats who receive proper care, a diagnosis of lymphoma often is not a catastrophe.
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