Intestinal lymphoma is the most common GI cancer in cats, typically presenting as chronic vomiting, diarrhea, and progressive weight loss in middle-aged to senior cats. The low-grade (small cell) form responds well to chlorambucil + prednisolone, with median survival times of 2–3 years. The aggressive (large cell) form has a much shorter prognosis.
Last reviewed: June 2026
What Is Cat Intestinal Lymphoma?
Intestinal lymphoma is a malignant proliferation of lymphocytes within the wall of the small or large intestine. It is the most frequently diagnosed gastrointestinal tumor in cats, accounting for approximately 50–75% of all GI neoplasia cases in this species.
Veterinary oncologists classify feline intestinal lymphoma into two main grades:
- Low-grade (small cell / lymphocytic) lymphoma (LGAL) — the most common form; characterized by small, well-differentiated T-lymphocytes infiltrating the intestinal mucosa. Clinical signs develop slowly and may mimic inflammatory bowel disease (IBD). This form responds remarkably well to medical management.
- High-grade (large cell / lymphoblastic) lymphoma (HGAL) — aggressive, rapidly progressing; often presents with a palpable abdominal mass and severe systemic illness. Median survival even with treatment is 2–4 months.
Distinguishing between the two grades and differentiating LGAL from IBD requires biopsy — it cannot be done on ultrasound appearance alone.
Signs of Intestinal Lymphoma in Cats
- Chronic intermittent vomiting — often occurring 1–5 times per week
- Progressive weight loss — the most consistent sign; owners often describe a cat that is eating well but losing body mass
- Diarrhea — watery or semi-formed; may be intermittent
- Increased appetite (polyphagia) — especially in LGAL, where nutrient malabsorption drives hunger
- Decreased appetite in HGAL cases as disease becomes systemic
- Palpable thickened bowel loops or abdominal mass — felt during vet exam
- Lethargy and reduced activity as disease progresses
- Jaundice — if liver is involved
Affected cats are typically older: the median age at diagnosis is 10–13 years. There is no strong breed predisposition, though Siamese cats may have an elevated risk for high-grade forms.
Diagnosis: Separating Lymphoma from IBD
Chronic vomiting and weight loss in a senior cat have a broad differential including IBD, hyperthyroidism, chronic kidney disease, and exocrine pancreatic insufficiency — all of which must be excluded or identified before lymphoma is confirmed.
Diagnostic workup includes:
- Bloodwork + urinalysis — checks for CKD, hyperthyroidism, diabetes, anemia; LGAL cats often show mild hypoproteinemia (low albumin/globulin)
- Serum cobalamin (B12) and folate — very low B12 is characteristic of severe small intestinal disease and predicts poor prognosis; B12 supplementation is often part of treatment
- Abdominal ultrasound — assesses intestinal wall thickness, layering, and lymph node involvement; mesenteric lymph node enlargement is common; wall thickness >7–9 mm suggests HGAL
- Fine needle aspirate of mesenteric lymph nodes — can confirm lymphoma when nodes are enlarged and accessible
- Endoscopic biopsy (gold standard for LGAL) — full mucosal biopsy via endoscopy or laparoscopy; PCNA/Ki67 immunohistochemistry and clonality testing (PARR) distinguish reactive lymphocyte populations (IBD) from clonal lymphoma
As described in Withrow & MacEwen's Small Animal Clinical Oncology, PARR (PCR for antigen receptor rearrangements) testing on biopsy specimens achieves >90% diagnostic accuracy in differentiating LGAL from IBD when combined with histopathology.
Treatment by Grade
Low-grade (small cell) lymphoma: The standard protocol is chlorambucil + prednisolone given orally at home. This simple two-drug protocol achieves clinical remission in 60–70% of cats, with median survival times of 22–30 months. Some cats live 3–4+ years in remission. The AAFP Senior Care Guidelines (2021) emphasize regular nutritional reassessment every 2–3 months during chemotherapy, including weight and body condition scoring, as lean muscle loss accelerates during treatment (AAFP Senior Care Guidelines, 2021).
B12 (cobalamin) deficiency should be corrected early: subcutaneous cobalamin injections weekly for 6 weeks, then monthly, dramatically improve response rates in B12-deficient cats.
High-grade (large cell) lymphoma: Multi-agent chemotherapy (COP or CHOP protocols: cyclophosphamide, doxorubicin/vincristine, prednisolone) achieves partial or complete remission in 50–65% of cats, but median survival is only 2–4 months. Some cats respond for 6–9 months.
Appetite stimulants (mirtazapine), anti-nausea drugs (maropitant, ondansetron), and nutritional support are critical supportive measures during aggressive chemotherapy.
Monitoring and Quality of Life
Cats with LGAL maintained on chlorambucil + prednisolone typically have good quality of life. Home monitoring signs include appetite, weight (weekly weigh-ins on a postal scale), frequency of vomiting, stool consistency, and energy. A monthly vet visit initially, moving to every 2–3 months once stable, allows dose adjustment and detection of relapse.
Relapse is managed by stepping up to more aggressive chemotherapy, adding lomustine, or switching protocols. Many cats achieve a second remission.
When to See a Vet
Call your vet today if:
- Your cat has been vomiting more than once a week for several weeks
- A senior cat is losing weight despite eating well
- You feel a lump or thickening in your cat's belly
Go to the ER immediately if:
- Your cat collapses or is unable to stand
- There is blood in vomit or diarrhea
- Your cat has not eaten in 48+ hours and is lethargic or jaundiced
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Frequently Asked Questions
What is the life expectancy for a cat with intestinal lymphoma? It depends on the grade. Low-grade (small cell) lymphoma managed with chlorambucil + prednisolone carries a median survival of 22–30 months — with some cats living 3–4 years in remission. High-grade lymphoma typically has a median survival of 2–4 months even with aggressive chemotherapy. Grade determination by biopsy is essential before any prognosis is given.
How much does lymphoma treatment cost for cats? Diagnosis (ultrasound, biopsy, histopath, PARR testing) runs $800–2,000. Chlorambucil + prednisolone for LGAL costs approximately $50–100/month at cat doses — very manageable. CHOP-based chemotherapy for HGAL costs $3,000–6,000 for a full protocol. Monthly monitoring visits add $100–250 each. Total LGAL cost over a 2-year remission: roughly $3,000–6,000 including monitoring.
Can intestinal lymphoma in cats be mistaken for IBD? Yes — LGAL and IBD can look identical on ultrasound and even on routine biopsy. PARR clonality testing or immunohistochemistry (CD3/CD20 staining pattern, Ki67 index) is required for a definitive distinction. This distinction matters because IBD is treated with diet and steroids, while LGAL requires chlorambucil. Starting chlorambucil in a cat with IBD is not harmful, but failing to add it in a cat with LGAL is.
Does my cat need to stay at the hospital for chemotherapy? For LGAL, no — treatment is given entirely at home as oral tablets. For HGAL, some drugs (vincristine, doxorubicin) are given by IV at the clinic, but the cat goes home the same day in most cases. Hospitalization is only required when complications (severe bone marrow suppression, GI crisis) occur.
Are there dietary changes that help cats with intestinal lymphoma? Yes. A highly digestible, high-protein diet helps counter lean muscle loss. Hydrolyzed protein or novel protein diets reduce antigen load in the gut. If B12 is low, supplementation is critical. Tube feeding support may be needed if appetite suppression is significant. Your vet may recommend an appetite stimulant (mirtazapine transdermal patch) alongside chemotherapy.
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