Renal Lymphoma

TL;DR. Renal lymphoma is a serious form of cancer affecting the kidneys of dogs and cats, often leading to kidney enlargement, increased thirst and urination, and weight loss.

Renal lymphoma typically causes bilateral renomegaly, where both kidneys become significantly enlarged.

What is it?

Renal lymphoma, also known as renal lymphosarcoma, is a form of cancer that primarily targets the kidneys. Unlike primary kidney cancers, which start directly within the kidney tissue, lymphoma is a cancer of the lymphatic system. Specifically, it involves the uncontrolled division of lymphocytes, a type of white blood cell responsible for immune defense. When lymphoma develops outside of the lymph nodes, it is referred to as "extranodal" lymphoma. The kidneys are a common site for this extranodal presentation, particularly in cats.

In affected pets, the disease typically causes bilateral renomegaly, which is the medical term for the enlargement of both kidneys. As the cancerous lymphocytes invade the kidneys, they multiply and gradually replace the normal, healthy kidney tissue. This progressive infiltration disrupts the kidneys' delicate filtration systems, leading to a decline in function and, eventually, kidney failure.

In cats, renal lymphoma is frequently associated with the alimentary form of the disease, meaning the cancer may also be present in the gastrointestinal tract or surrounding lymph nodes. Because the kidneys play a vital role in filtering waste from the blood, maintaining fluid balance, and producing hormones, the systemic impact of this disease is profound. Understanding the signs and diagnostic pathways is crucial for pet owners navigating this challenging diagnosis.

Causes & risk factors

Like most veterinary cancers, the exact underlying cause of renal lymphoma remains largely unknown. It is generally considered a multifactorial disease, resulting from a complex interaction of genetic predispositions and environmental factors. In cats, historical links existed between lymphoma and the Feline Leukemia Virus (FeLV), though modern vaccination and screening have shifted the demographics of affected feline patients.

Certain breeds of both dogs and cats show a higher statistical predisposition to developing this condition:

• Siamese Cats: This breed has a well-documented, higher risk of developing various forms of lymphoma, including renal lymphoma.
• Oriental Longhairs: Closely related to the Siamese, these cats also show an increased susceptibility to the disease.
• Rottweilers: In the canine world, Rottweilers are known to have a higher incidence of lymphoma, including rare extranodal forms.
• Persian Greyhounds: This breed has also been identified as having an elevated risk for developing lymphoma.

While these breed associations exist, renal lymphoma can affect any mixed-breed or purebred dog or cat, typically occurring in middle-aged to older animals.

Signs to watch for

Because renal lymphoma directly damages the kidneys, many of the clinical signs mimic those of chronic kidney disease or kidney failure. The symptoms can develop gradually or appear suddenly as the functional capacity of the kidneys is compromised.

Key symptoms to watch for include:

• Renomegaly (Cardinal): Enlargement of one or both kidneys. While you may not be able to feel this yourself, your veterinarian will easily detect it during a physical examination of your pet's abdomen.
• Polyuria (Common): An increase in the volume and frequency of urination, caused by the kidneys losing their ability to concentrate urine.
• Polydipsia (Common): Significantly increased thirst and water consumption as the body attempts to compensate for fluid loss.
• Emaciation (Common): Progressive, severe weight loss and muscle wasting, often accompanied by a poor appetite.
• Azotemia (Common): The buildup of nitrogenous waste products (like urea and creatinine) in the blood, which leads to internal toxicity and feelings of nausea.
• Anemia (Common): A low red blood cell count. The kidneys produce erythropoietin, a hormone that signals the bone marrow to make red blood cells. When kidney tissue is damaged by cancer, this hormone production drops.
• Renal failure (Occasional): Complete or near-complete loss of kidney function, resulting in severe systemic illness.

Increased thirst (polydipsia) and weight loss are common signs of kidney dysfunction associated with renal lymphoma.

How vets diagnose it

Diagnosing renal lymphoma requires a systematic approach to rule out other causes of kidney enlargement, such as polycystic kidney disease or benign cysts. Your veterinarian will start with a thorough physical exam, focusing on abdominal palpation to assess the size, shape, and symmetry of the kidneys.

Key diagnostic tests include:

• Renal Ultrasonography: This is the primary imaging tool used to visualize the kidneys. Ultrasound allows the vet to see the internal architecture of the organs, identify whether the enlargement is solid or fluid-filled (cystic), and assess if other abdominal organs or lymph nodes are involved.

• Fine-Needle Aspiration (FNA) of the Kidney: This is a highly effective, minimally invasive procedure. Under ultrasound guidance, a tiny needle is inserted into the kidney to collect a sample of cells. These cells are then examined under a microscope (cytology). As noted in a leading veterinary textbook on diagnostic cytology:

  "Renal cytology is especially diagnostically useful for the rapid confirmation of lymphoma and carcinoma in cats, with sensitivity, specificity, positive predictive value, and negative predictive value all reported as 100%. A similar high degree of sensitivity for detecting lymphoma (100%) and moderate sensitivity for all types of renal neoplasia (78%) has been shown in dogs."

• Histological Confirmation: If cytology results are unclear, a tissue biopsy may be performed to obtain a larger sample for microscopic evaluation.

• Immunophenotyping: This specialized laboratory test determines whether the lymphoma consists of abnormal B-cells or T-cells. This information is highly valuable, as B-cell and T-cell lymphomas can respond differently to specific chemotherapy drugs.

Renal ultrasonography is a vital tool for visualizing kidney structure and guiding diagnostic needle biopsies.

Treatment options

Because renal lymphoma is a systemic cancer, surgical removal of the affected kidney is rarely recommended unless the disease is strictly confined to one side and the other kidney is fully functional—a very rare scenario. Instead, chemotherapy is the primary line of defense.

Chemotherapy

Chemotherapy protocols for renal lymphoma are designed to kill rapidly dividing cancer cells while preserving as much healthy kidney function as possible. Two primary antineoplastic agents commonly utilized in these protocols include:

• Cytarabine: This is an antineoplastic (chemotherapy) drug that is particularly useful in treating lymphoma. It works by interfering with DNA synthesis in cancer cells, preventing them from multiplying. It is sometimes selected because of its ability to penetrate the central nervous system, which is a potential site of spread for feline renal lymphoma.
• Lomustine: This is an alkylating agent belonging to the nitrosourea class of drugs. It works by damaging the DNA of cancer cells, leading to cell death. Lomustine is administered orally and is often integrated into multi-agent chemotherapy protocols.

Supportive Care

Alongside chemotherapy, aggressive supportive care is essential to manage kidney dysfunction and maintain your pet's quality of life. This may include intravenous or subcutaneous fluid therapy to flush toxins from the blood, anti-nausea medications to combat uremic toxins, appetite stimulants, and specialized kidney-friendly diets.

Prognosis

Specific long-term prognosis statistics for renal lymphoma are limited in our primary reference materials, and outcomes can vary significantly based on how early the disease is caught, the species affected, and how well the animal tolerates chemotherapy. Generally, renal lymphoma carries a guarded prognosis because it represents an advanced, extranodal form of cancer that directly compromises a vital organ system.

Without treatment, the disease progresses rapidly, leading to fatal kidney failure within weeks. However, with appropriate chemotherapy, many pets can achieve temporary remission, restoring their quality of life and extending their time with their families. Your veterinary oncologist will help you weigh the potential benefits of treatment against your pet's current comfort level.

Prevention

There is no known way to prevent renal lymphoma. Because the exact triggers of the mutation in the lymphocytes are unknown, preventive measures focus entirely on early detection.

For breeds known to be at higher risk, such as Siamese cats or Rottweilers, regular veterinary wellness exams—including routine blood work, urinalysis, and abdominal palpation—are the best tools for catching kidney changes before severe clinical signs develop.

When to call your vet

You should contact your veterinarian if you notice any changes in your pet's drinking or urinating habits, unexplained weight loss, or a general decline in energy.

Seek immediate emergency veterinary care if your pet exhibits severe vomiting, complete refusal to eat, extreme lethargy, or signs of acute kidney failure, such as a sudden inability to produce urine. These are critical red flags that require urgent medical intervention.

For specific breeds

If you own a Siamese cat, Oriental Longhair, Rottweiler, or Persian Greyhound, it is important to be proactive about their health. Inform your veterinarian of their breed-specific predispositions. Incorporating routine blood chemistry panels and urinalysis into their annual or bi-annual veterinary visits can help monitor kidney health and detect abnormalities early, when treatment is most likely to be effective.

Sources

• Cowell and Tyler's Diagnostic Cytology and Hematology of the Dog and Cat, 5th Edition, p. 385.
• Internal Medicine, 5th Edition, p. 670, 1196.