Feline small cell GI lymphoma: A cancer that overlaps with IBD

Developing slowly over months to years, feline small cell gastrointestinal (GI) lymphoma can be difficult to detect.¹ With this type of cancer resembling many of the common digestive issues cats often experience, understanding the disease, warning signs, diagnosis, and treatment is important to ensure the wellbeing of feline patients suffering from chronic GI symptoms.

GI lymphoma in cats is divided between small cell and large cell. Unlike small cell lymphoma, signs for large cell lymphoma develop quickly, over days to weeks, and prognosis is poorer.²

According to North Carolina State Veterinary Hospital, cats with large cell GI lymphoma receiving CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisolone) therapy have a prognosis of 6 to 9 months.² Meanwhile, cats with small cell GI lymphoma have a longer prognosis of typically 2 to 3 years or more, but chronic treatment with oral medications is required.²

The ins and outs of small cell GI lymphoma

Small cell GI lymphoma forms in the digestive tract. Affecting lymphocytes—immune cells involved in fighting off infection—, lymphoma causes uncontrolled cell growth and loss of normal cell function. According to Texas A&M, the GI tract is home to a high number of lymphocytes, making it a common site of lymphoma in feline patients.¹ In fact, small cell GI lymphoma is the most common type of lymphoma in cats,³ and the most frequently diagnosed digestive tract cancer in these animals.¹

“Small cell GI lymphoma is the most common cancer of a cat’s digestive system and a highly prevalent feline cancer overall,” Regina Hayburn, DVM, DACVIM (Oncology), a clinical assistant professor of medical oncology at Texas A&M’s Department of Small Animal Clinical Sciences, said in the Texas A&M report.¹ “It can form anywhere along the digestive tract, including the stomach, small intestine, or colon.”

IBD and small cell GI lymphoma are thought to be closely related, representing different stages of the same underlying process. Veterinary researchers have found that gastrointestinal inflammatory lesions, a major characteristic of IBD, often coexist with small cell GI lymphoma.⁴ This overlap has led to the proposition that chronic inflammatory lesions might progress to lymphoma over time.⁴ As such, many researchers and veterinarians have described small cell GI lymphoma as being a “spectrum of disease” with IBD.^1,4

The chronic inflammation seen in IBD leads to abnormalities in the intestinal walls that can affect the movement and absorption of food and water in the digestive system. This disruption consequently leads to chronic GI symptoms.

With GI lymphoma being a spectrum disease with IBD, clinical signs are largely the same. “Because of the impaired motility and absorption, chronic vomiting and diarrhea are common, along with weight loss and decreased appetite, although some cats maintain a normal or even increased appetite in early stages,” Hayburn said in the Texas A&M report.¹ “As the disease progresses, cats often stop eating, vomit more frequently, and become increasingly lethargic and generally unwell due to chronic illness and weight loss.” Bloody stools may also be a sign of small cell GI lymphoma and IBD.

Diagnosing small cell GI lymphoma

Taking bloodwork of feline patients suffering from chronic GI issues is an important first step to obtaining a proper diagnosis, according to Texas A&M.

Abdominal ultrasounds may show thickened GI wall layers or changes in the intestinal walls, but it cannot confirm whether cancer is present. Definitive diagnosis of GI lymphoma requires a tissue biopsy for histopathologic examination.

Tissue samples for biopsy can be obtained either through endoscopy or surgery. Hayburn noted that endoscopic biopsies are less invasive but provide only small tissue samples. Meanwhile, surgical biopsies allow for collection from different areas of the intestine and include full intestinal thickness samples, but they require an open-abdomen surgery.¹

Once tissue is collected, veterinarians can perform additional tests to differentiate GI lymphoma from other conditions like irritable bowel disease, which can appear similar on imaging but require different treatment.¹ These tests may include histopathology, immunohistochemistry, and polymerase chain reaction for polymerase chain reaction for antigen receptor rearrangements (PARR).

Conventional treatment

Treating small cell GI lymphoma involves long-term chemotherapy. “The most common treatments involve oral chemotherapy (Chlorambucil) given at home and oral steroids (prednisolone). These medications can be given long-term and help control this disease for years,” Hayburn said.¹ She explained that this therapy is “generally well tolerated.”

Whole abdomen radiation therapy—a new treatment option?

Still, “oral medications can be challenging for some cats,” Hayburn noted. For feline patients who struggle with this form of medication and patients facing other therapy difficulties, Texas A&M is exploring new treatment options.

Currently, Hayburn is recruiting participants for a clinical trial that will evaluate whole abdomen radiation therapy as a treatment for feline small cell GI lymphoma. The study will examine the use of whole abdomen radiation therapy in cats whose lymphoma has relapsed after receiving previous standard-of-care treatment.⁵

“This would make treatment easier for cats who are difficult to orally medicate or who don’t like frequent veterinary visits,” said Hayburn.¹

For the study, researchers aim to assess the safety and practicality of radiation therapy for cats with relapsed small cell GI lymphoma.⁵ Participants will undergo a series of radiation treatments over several days, with follow-up exams to monitor response and overall health.

According to Hayburn, effectiveness of treatment can be measured by how well the patient’s symptoms are being managed, rather than imaging results. “Abdominal ultrasounds might still show visible signs of the cancer even when the cat is feeling much better,” Hayburn said in the university report.¹ “As long as the cat’s physical symptoms are managed—where the cat is eating well, gaining weight, and having minimal to no vomiting and diarrhea—the treatment plan is likely effective and doesn’t need to be changed.”

Takeaway

Understanding feline small cell GI lymphoma is key to ensuring the condition does not go undiagnosed. With the disease being closely interconnected with IBD, conducting a biopsy to rule out cancer in patients with chronic GI symptoms can help veterinarians make an accurate diagnosis and guide appropriate treatment before the disease progresses.

References

1. Small cell GI lymphoma: A hidden cancer behind feline digestive issues. Texas A&M University Veterinary Medical & Biomedical Sciences. December 11, 2025. Accessed January 7, 2025. https://vetmed.tamu.edu/news/pet-talk/feline-gi-lymphoma/
2. Medical oncology: Feline lymphoma. North Carolina State University. Accessed January 7, 2025. https://hospital.cvm.ncsu.edu/services/small-animals/cancer-oncology/oncology/feline-lymphoma/
3. Common types of cancer in cats. University of Wisconsin-Madison. Accessed January 7, 2025. https://uwveterinarycare.wisc.edu/common-types-of-cancer-in-cats/#:~:text=Small%20cell%20gastrointestinal%20(GI)%20lymphoma%20is%20the,GI%20lymphoma%20typically%20respond%20well%20to%20treatment.
4. Marsilio S, Pilla R, Sarawichitr B, et al. Characterization of the fecal microbiome in cats with inflammatory bowel disease or alimentary small cell lymphoma. Sci Rep. 2019;9:19208. https://doi.org/10.1038/s41598-019-55691-w
5. Evaluating whole abdomen radiation therapy as a treatment for feline small cell gastrointestinal lymphoma. Studypages. Accessed January 8, 2025. https://studypages.com/s/evaluating-whole-abdomen-radiation-therapy-as-a-treatment-for-feline-small-cell-gastrointestinal-lymphoma-358215/?ref=gallery