Gastrointestinal (GI) lymphoma is the most common type of feline GI cancer, typically affecting middle-aged to older cats. Clinical signs commonly include severe weight loss with or without anorexia, vomiting, or diarrhea. Earlier diagnosis and treatment hold the promise of greater survival times. However, current diagnostic techniques based on microscopic assessment of GI biopsies make it difficult in some cases to distinguish inflammatory bowel disease (IBD – a non-cancerous inflammatory invasion of immune cells into the intestinal wall of cats) from lymphoma. The objective of this study is to define the inflammatory and immune responses of the gastrointestinal tracts of cats with GI lymphoma.