Lymphoma (Lymphosarcoma) in Cats

What is lymphoma?

Lymphoma (lymphosarcoma) is a cancer that begins in infection-fighting cells of the immune system, called lymphocytes, which are a type of white blood cells. It is responsible for almost one-third of all cancers in cats.

The lymphatic system is a network of vessels located throughout the body. These vessels transport lymph, a clear fluid containing protein, water, minerals and white blood cells. The role of the lymphatic system is to:

• Filter out bacteria and debris
• Manage fluid levels in the blood
• House white blood cells (also known as lymphocytes)

Lymphoma in cats behaves differently from lymphoma in humans and dogs, which tends to accumulate in the lymph nodes, but in cats, it tends to accumulate in the abdominal cavity, usually the small intestine.

Predisposing factors

• Viral infections (FIV and FeLV): Cats with feline leukemia virus are 60 times more likely to acquire lymphosarcoma than those without. Cats with FeLV are 5-6 times more likely to develop lymphosarcoma.
• Immunosuppression: Due to FIV, FeLV, or immunosuppressive drugs.
  
• Genetics: There is a higher incidence in Manx, Siamese, and Burmese cats.
• Inflammatory bowel disease: Over time, chronic inflammation can progress into low-grade lymphoma.
  
• Environmental – Cats living in smoking households are twice as likely to acquire lymphosarcoma. [2]

The average age of cats with lymphosarcoma is three years for those who are FeLV positive and 9-12 years for cats who are FeLV negative.

Symptoms

Clinical signs of lymphosarcoma vary depending on the organ/tissues involved. The gastrointestinal system is most commonly affected.

General symptoms

• Enlarged lymph nodes
• Loss of appetite (anorexia)
• Weight loss
• Depression
• Lethargy
• Other signs depend on the specific location

Multicentric

Multicentric lymphoma affects multiple lymph nodes and organs. Spleen, liver and bone marrow may also be involved.

• Enlarged lymph nodes
• Lethargy
• Loss of appetite
• Fever
• Depression

Mediastinal

Also known as thymic, mediastinal lymphosarcoma occurs in the thymus, which is located in the chest (between the lungs) and anterior mediastinal lymph nodes and can cause fluid to accumulate around the lungs (pleural effusion).

Mediastinal lymphoma is the most common lymphoma in FeLV positive cats and occurs in younger cats around 2 to 3 years of age.

• Difficulty breathing
• Coughing

Alimentary

Alimentary lymphosarcoma occurs in the stomach, intestines, liver, and spleen. It is the most common form of lymphoma. [1] The average age for alimentary lymphoma is 8 to 9 years. There are two types of lymphosarcoma of the gastrointestinal tract. High grade (large cell), which is more aggressive or low grade (small cell) and cats with high-grade lymphoma can get sick within days to weeks whereas cats with low-grade lymphoma get sick over weeks to months.

Symptoms of alimentary lymphosarcoma may include:

• Vomiting
• Diarrhea
• Weight loss
• Loss of appetite
• Fever
• Loss of coat condition
• A palpable abdominal mass (high grade) may be present or thickening of the intestine

Extranodal/miscellaneous

Extranodal lymphoma or miscellaneous lymphoma occurs most commonly in the kidneys, eyes, nasal cavity, CNS, skin or heart.

Diagnosis

The veterinarian will perform a complete physical examination and obtain a medical history from you. Physical examination may reveal swellings in the lymph nodes or thickening of the gastrointestinal tract. Biopsies are required to definitively diagnose lymphoma.

Diagnostic workup:

• Complete blood count: Anemia (low red blood cell count) and circulating lymphoblasts (immature cells usually found in the bone marrow, but may be present in the blood in cats with lymphosarcoma).
• Biochemical profile and urinalysis: This can reveal the overall health of your cat. These tests may also show abnormalities in affected organs such as abnormal kidney function, elevated liver enzymes, hypercalcemia.
• FeLV and FIV test.
• Ultrasound: May reveal abnormalities such as thickening of the intestines, abdominal masses or enlarged organs.
• Chest x-ray: For cats with mediastinal lymphoma to evaluate the lungs and heart for fluid build-up.
• Fine needle aspiration/cytology or full-thickness biopsy/histopathology: To confirm the presence of lymphosarcoma.
• Bone marrow aspirate/cytology: To confirm a diagnosis of bone marrow lymphosarcoma and document bone marrow involvement with other forms of lymphosarcoma.
• Maldigestion profile: This can evaluate the cat for low levels of vitamins and minerals; many cats with GI disease are low in vitamin B12.

Staging:

Once a diagnosis of lymphosarcoma has been made, clinical staging will be necessary to determine the extent of tumour involvement.

1. I: Single lymph node involvement only.
2. II: Several lymph nodes involved within a regional area.
3. III: Generalised lymph node involvement.
4. IV: Involvement of the liver and or spleen.
5. V: Any of the above with bone/bone marrow involvement or other organs (skin, gastrointestinal, kidneys etc.)

Treatment

Chemotherapy: The mainstay of treatment for lymphosarcoma in cats is chemotherapy; a multi-agent chemotherapy protocol is most common which combines several chemotherapy drugs to treat high-grade lymphoma. Cats with low-grade lymphoma may be prescribed prednisone along with oral chemotherapy drugs.

• CHOP chemotherapy – Cyclophosphamide, doxorubicin, vincristine and prednisone.
• CVP chemotherapy – Cyclophosphamide, vincristine and prednisolone.

Chemotherapy is well tolerated by cats, although they may experience a few side effects such as anorexia or lethargy. Lymphosarcomas respond well to chemotherapy, but this treatment is not curative, it can, however, give the cat some extra time.

Surgery: If the tumour is small and easy to access.

Radiotherapy: Cats with nasal lymphosarcoma will initially be treated with radiotherapy to target the cells; chemotherapy will be introduced following radiotherapy treatment.

Supportive care: Fluids to correct dehydration and nutritional support, supplementation anti-nausea drugs and appetite stimulants where necessary.

Remission is achieved in 74% of cats, some cancer cells survive, but numbers are so low they cannot be detected. Eventually, cancer will return, and a new protocol will be necessary to re-establish remission. Unfortunately, there will come a time when the cancer cells become resistant to all chemotherapy protocols.

The average survival time is 6-9 months; without treatment, it is 4-6 weeks.

Prognosis

The prognosis varies depending on several factors such as the location and extent of the tumours and the FeLV status of the cat, response to chemotherapy, stage of the disease.

• The expected lifespan of a cat who receives no treatment is one month.
• Cats who receive steroid only treatment can live up to two months.
• Cats who receive chemotherapy can live for 12 months or more.

References:

[1] The Feline Patient – Gary D. Norsworthy, Mitchell A. Crystal, Sharon K. Fooshee and Larry P. Tilley.

[2] Science Daily

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