Feline lymphoma, a prevalent cancer in cats, targets the lymphatic system, a complex network vital to nearly every bodily function. According to Dr. Margaret McEntee, a veterinary oncology professor at Cornell University, lymphoma is the most frequently diagnosed cancer type in felines. Understanding this disease is crucial for cat owners to ensure timely diagnosis and appropriate care for their beloved pets.
The lymphatic system in cats is an intricate network of organs and tissues, including the thymus gland, spleen, bone marrow, and gut-associated lymphoid tissue. This system plays a critical role in transporting essential substances and defending against harmful invaders throughout the body. Lymph, a vital fluid, circulates through lymphatic vessels and lymph nodes—small, bean-shaped tissues located throughout the body, such as in the neck, groin, and behind the knees. This fluid and vessel network is responsible for delivering oxygen and nutrients, removing waste, absorbing fats, and eliminating pathogens.
Historically, mediastinal lymphoma (chest cavity) and multicentric lymphoma (system-wide) were common. These forms were often linked to feline leukemia virus (FeLV) and, to a lesser extent, feline immunodeficiency virus (FIV). Thanks to increased testing, isolation of infected cats, and FeLV vaccines, these virus-related lymphomas are less frequent today. Currently, gastrointestinal lymphoma is the most common type, presenting unique challenges in treatment and prognosis compared to lymphoma in other locations.
Gastrointestinal Lymphoma: Recognizing the Signs
Gastrointestinal lymphoma, affecting the digestive tract, manifests through various clinical signs. Cat owners should be vigilant for symptoms such as unexplained weight loss, vomiting, diarrhea, and changes in appetite—either decreased or increased. During a veterinary examination, physical findings might be subtle or include palpable thickened intestines or abdominal masses. Interestingly, bloodwork in cats with gastrointestinal lymphoma often appears normal. Ultrasound imaging of the intestinal tract may reveal thickening or masses, but can also present as normal, making diagnosis challenging as these signs can mimic Inflammatory Bowel Disease (IBD).
Obtaining biopsies of the intestinal tract is essential for a definitive lymphoma diagnosis. Endoscopy, a minimally invasive procedure using a flexible camera to visualize and sample the stomach and upper intestines, can be employed. Alternatively, surgical biopsies, though more invasive, can provide larger tissue samples from broader areas of the intestine, potentially leading to a more accurate diagnosis. Microscopic examination of biopsy samples not only confirms lymphoma but also differentiates between small cell and large cell lymphoma subtypes, which have significant implications for treatment and prognosis.
Small cell lymphoma is generally considered an indolent, or less aggressive, form of the disease. Treatment for small cell gastrointestinal lymphoma is often effectively managed at home using a combination of prednisolone (a steroid) and chlorambucil (an oral chemotherapy drug). Over 90% of cats with small cell lymphoma achieve remission with this protocol. While these medications require regular monitoring for potential side effects, most cats tolerate them well, with survival times typically ranging from two to four years post-diagnosis.
Large cell lymphoma in the gastrointestinal tract is a more aggressive and malignant form, associated with a poorer prognosis. It may present with intestinal masses, in which case surgery might be considered. However, treatment strategies and prognosis are generally similar to those for multicentric lymphoma, which is discussed below.
Lymphoma Beyond the Gastrointestinal Tract
Lymphoma can develop in various locations throughout a cat’s body due to the widespread nature of the lymphatic system. While less common in cats than in dogs, lymphoma can affect peripheral lymph nodes, which are palpable as enlarged lumps in areas like the neck, shoulders, and behind the knees. It can also occur in internal lymph nodes, the chest cavity (mediastinal lymphoma), liver, spleen, kidneys, nasal cavity, eyes, or central nervous system.
Symptoms of lymphoma outside the gastrointestinal tract are diverse and depend on the affected location. They can range from non-specific signs like weight loss, reduced appetite, and lethargy, to more specific issues such as breathing difficulties, nasal discharge, skin masses, or seizures. Diagnosing lymphoma typically involves a thorough physical examination and diagnostic tests to confirm or rule out the disease. These tests often include a complete blood cell count, blood chemistry panel, urinalysis, chest X-rays, microscopic analysis of lymph node tissue samples (cytology or biopsy), and abdominal ultrasound to assess the liver and spleen, common sites of lymphoma involvement.
While cats of any age can develop lymphoma, it is more frequently diagnosed in cats aged 10 to 12 years. Unvaccinated outdoor cats face a higher risk due to increased exposure to FeLV. Recent research also indicates that cats exposed to tobacco smoke are at an elevated risk of developing gastrointestinal lymphoma.
Treatment and Prognosis for Feline Lymphoma
Treatment for most types of feline lymphoma primarily involves chemotherapy. A veterinary oncologist will tailor a chemotherapy protocol, often involving intravenous administration of drug combinations, typically on a weekly basis for several weeks, depending on the cat’s response. Regular monitoring is crucial to manage potential side effects, although chemotherapy is generally better tolerated in animals than in humans. Common side effects can include decreased white blood cell counts, vomiting, and reduced appetite. Depending on the lymphoma type and location, additional treatments may be necessary. For instance, surgery might be recommended to remove intestinal masses in large cell lymphoma, and radiation therapy can be highly effective for nasal lymphoma.
Prognosis varies significantly based on the lymphoma’s location and type. However, with aggressive chemotherapy protocols, 50-80% of cats can achieve remission of clinical signs, with an average remission duration of four to nine months.
For cases where chemotherapy or radiation therapy are not feasible options, palliative care with prednisolone (steroid) alone can be considered. This approach can provide temporary symptom improvement or remission for two to four months. While steroid-only treatment offers a less favorable prognosis compared to chemotherapy, it can be administered at home, reducing veterinary visits and treatment costs.
Prevention and Early Detection
While lymphoma cannot be entirely prevented, cat owners can take steps to minimize their cat’s risk. Vaccination against FeLV, preventing contact with FeLV or FIV-infected cats, and ensuring a smoke-free environment are crucial preventative measures. Early detection significantly improves a cat’s chances of successful treatment. Therefore, Dr. McEntee recommends that all cats aged seven years and older undergo semi-annual physical examinations, including blood chemistry testing and thorough palpation, to facilitate early diagnosis and intervention.
Last updated 2021
