[Written by a Veterinarian] What is Lymphoma in Cats? Symptoms, Causes, Treatment, and Dietary Care

Feline lymphoma accounts for approximately 30% of malignant tumors in cats, making it a highly prevalent neoplasm. Early symptoms are diverse and include "seeming slightly off," "weight loss," and "the presence of lumps." Early detection and appropriate treatment are crucial for lymphoma. In this article, a veterinarian explains the disease based on actual clinical experience.

What is feline lymphoma?

What kind of disease is lymphoma?

Lymphoma is a malignant tumor that develops when lymphocytes—a type of immune cell—become cancerous. Lymphocytes play a role in attacking bacteria and viruses that enter the body and producing antibodies to fight infections. Lymphocytes are produced in the bone marrow and, after maturing in the bone marrow or thymus, migrate to locations called lymphoid tissues, such as lymph nodes and the spleen, to prepare for the intrusion of pathogens. They also patrol the entire body by circulating through the blood from lymphoid tissues.

Lymphoma is a malignancy where the lymphocytes themselves become cancerous, leading to the proliferation of these transformed cells outside the bone marrow. Because lymphocytes exist not only in the blood but throughout the body, lymphoma has often already spread systemically by the time it is discovered.

Because lymphoma responds well to anti-cancer drugs, chemotherapy is the preferred treatment.

Common types of feline lymphoma

Lymphoma is classified based on the site of origin.

Types include mediastinal lymphoma, where the anterior mediastinal lymph nodes or thymus in the chest swell; gastrointestinal lymphoma, where tumors form in the intestinal tract or abdominal lymph nodes (mesenteric lymph nodes); multicentric lymphoma, where lymph nodes throughout the body swell; cutaneous lymphoma, where tumor cells appear on the skin; and extranodal lymphoma, which occurs in other sites (such as the central nervous system, kidneys, nose, or eyes).

Mediastinal and gastrointestinal types are the most common, with incidence rates of 20–50% and 30–50%, respectively. Multicentric lymphoma accounts for about 10%, while extranodal types are even less common.

High-risk ages and risk factors

Lymphoma typically occurs in relatively older cats aged 10 and over, but it can also occur in younger cats. Mediastinal lymphoma, in particular, is frequently seen in younger cats aged 3–5. It is known that cats with Feline Immunodeficiency Virus (FIV) or Feline Leukemia Virus (FeLV) are more prone to developing it; in particular, the risk is known to be high in cats infected with FeLV.

Although genetic factors have not been clearly identified, Siamese cats are considered a high-risk breed.

Major symptoms of feline lymphoma

Loss of appetite and weight loss

Since the common gastrointestinal lymphoma in cats involves tumors in the intestinal tract or abdominal cavity, loss of appetite and weight loss are observed. In renal (kidney) lymphoma, symptoms appear due to a decline in kidney function.

Lumps, swelling, and difficulty breathing

In multicentric lymphoma, where lymph nodes throughout the body swell, it is characteristic for the superficial lymph nodes (such as those in the neck, chest, or behind the knees) that are easily felt through the skin to become enlarged. Mediastinal lymphoma causes difficulty breathing due to swelling of the lymph nodes in the chest. Nasal lymphoma also causes breathing difficulties because tumors form within the nasal cavity; nasal lymphoma can cause the nose to swell and deform the face.

Gastrointestinal symptoms such as diarrhea and vomiting

Vomiting and diarrhea are common in gastrointestinal lymphoma. These occur due to intestinal obstruction caused by the tumor or inflammation. Mediastinal lymphoma can also lead to regurgitation due to compression of the esophagus. In this case, the cat will vomit undigested food shortly after eating.

These symptoms often appear with other diseases, and in the case of lymphoma, the disease can sometimes progress without any symptoms at all. In many cases, the disease is quite advanced when it is discovered, and it is rarely found at an early stage. Furthermore, because symptoms often emerge only after the disease has progressed, regular health checkups and early consultation are vital.

Treatment and prognosis

Chemotherapy

Because lymphoma responds well to anti-cancer drugs, chemotherapy is the first-line treatment. The primary approach is multi-agent chemotherapy, which uses several types of drugs. Chemotherapy is primarily administered via intravenous injection, but depending on the cat’s temperament, injections themselves may be difficult. In such cases, options such as oral-only treatment or drugs that can be administered via subcutaneous injection are proposed.

Lymphoma is a difficult tumor to cure, and long-term survival is challenging even with treatment. The survival time with chemotherapy is approximately 6–9 months.

Without treatment, the survival time is generally a few weeks to two months.

Options for surgery and radiation therapy

Typically, surgery is not performed for feline lymphoma. It may be an option for cutaneous lymphoma. While resection may be performed for diagnostic confirmation when a mass forms in the intestinal tract in gastrointestinal lymphoma, it is almost never performed for therapeutic purposes.

Like surgery, radiation therapy is not a first-line treatment. However, it may be used for certain types of lymphoma, such as nasal or mediastinal lymphoma.

Because lymphoma is a tumor that responds well to anti-cancer drugs, chemotherapy is used in combination with surgery or radiation. Therefore, the prognosis for surgery or radiation alone is unknown.

While a cure is difficult, palliative care can protect quality of life (QOL)

Unfortunately, lymphoma is a tumor that is difficult to cure with current veterinary medicine. Therefore, palliative care is essential. Palliative care is treatment that prioritizes the cat's QOL and aims to reduce pain and discomfort. For example, antiemetics are used for nausea, and analgesics are used for pain. If uncomfortable symptoms are relieved, there is a possibility that appetite and activity levels will increase. Although temporary, this can allow the cat to spend a peaceful time.

In my personal opinion, I feel that many owners are hesitant about chemotherapy. One reason is the cost. Typically, using a treatment protocol effective for lymphoma costs several hundred thousand yen for just one cycle of chemotherapy. Including tests, a single visit can cost nearly 50,000 yen.

When I explain treatment and costs, I am often asked, "Is there a cheaper treatment?" In those cases, I propose a treatment method using only oral steroid hormones, which is often included in treatment protocols. Steroids are relatively inexpensive and have antitumor effects, so they tend to be accepted. Furthermore, adding symptomatic treatment can be expected to improve QOL further.

This is merely a proposal I make as a practitioner, so it is necessary to discuss the actual treatment plan thoroughly with your primary veterinarian.

Feline lymphoma and dietary management

Benefits of incorporating therapeutic diets

Like most malignant tumors, lymphoma tends to cause progressive weight loss. This is not only due to decreased appetite, diarrhea, or vomiting, but also because the tumor itself consumes nutrients. Consequently, animals with malignant tumors enter a state called cachexia, where they lose weight continuously.

Diets for tumor patients differ from standard nutritional profiles. Tumors use carbohydrates (glucose) as their sole source of energy for growth. Therefore, a low-carbohydrate, high-protein diet is desirable, preferably one containing essential fatty acids (EPA and DHA). While there are no therapeutic diets specifically targeting tumors, there are diets classified as therapeutic that are low-carbohydrate, high-protein, easily digestible, or designed to improve cachexia. Since cats with lymphoma tend to lose weight, the key is to use therapeutic diets effectively to prevent weight loss.

Tips for when appetite declines (scent, temperature, and feeding methods)

Many cats with lymphoma experience a decrease in appetite. To prevent weight loss, it is necessary to make adjustments so they will eat at least something. Warming up food or softening it with water intensifies the scent, which can stimulate a cat's appetite. Gastrointestinal lymphoma causes intestinal obstruction, so cats may vomit if given too much food at once. Therefore, feeding small, frequent meals throughout the day is recommended.

If the cat is completely unable to eat, options such as antiemetics or appetite stimulants, or the insertion of a tube into the nose, esophagus, or stomach to administer liquid food, may be considered.

Precautions for multi-cat households (managing separately from other cats)

Because anti-cancer drugs are used during lymphoma treatment, it is better to keep the cat isolated to avoid exposing other cats to these drugs.

If the cat lives with other cats, you must ensure that the other cats are eating well. Use a crate or other method to isolate them during meal times to ensure your cat can eat enough food. Feeding them separately also allows you to keep track of their intake.

Summary | Facing feline lymphoma

Lymphoma, one of the most common malignancies in cats, often progresses silently, and it is not rare for it to be quite advanced by the time it is noticed. While it is common in older cats, it can occur from the age of three. Therefore, make sure to schedule regular health checkups once your cat passes the age of one. Additionally, lumps or weight loss can often be discovered by checking your cat's body on a daily basis. Check them while engaging in physical affection.

Unfortunately, lymphoma is a disease that is difficult to cure. Through appropriate treatment and dietary management, you can maintain your cat's QOL and allow them to spend peaceful, symptom-free time. Since it is an incurable disease, it is natural for owners to feel unsettled, but by supporting your cat with love until the end, your cat can feel secure.