Introduction 

An 82-year-old woman who had been evaluated in 2022 for iron-deficiency anemia and a positive fecal occult blood test. Gastroscopy and colonoscopy showed no abnormalities. She was lost to follow-up until 2025, when Primary Care requested a new colonoscopy due to altered bowel habits. 

Endoscopy 

Colonoscopy revealed flat polyps (Paris 0-IIa) smaller than 5 mm in the rectum, which were biopsied, demonstrating infiltration by mantle cell lymphoma, classic variant. As part of the staging work-up, an upper endoscopy was performed, showing erythematous areas with loss of glandular pattern and irregular vessels in the gastric fundus; in addition, 3–5 mm eroded nodular lesions were seen in the duodenal bulb. Both sites were biopsied, with results consistent with infiltration by the same lymphoma. 

A PET-CT scan demonstrated uptake in the gastric fundus, supra- and infradiaphragmatic lymph nodes, and intestinal involvement. Capsule endoscopy revealed multiple nodular lesions (3–5 mm) in the duodenal bulb, some of them eroded, compatible with mantle cell lymphoma. In the distal ileum, millimetric nodular lesions (2–3 mm), some eroded, were identified, highly suggestive of infiltration at this level. 

Comments/Conclusions 

Gastrointestinal mantle cell lymphoma is uncommon, with the small intestine being its most typical site of involvement. Endoscopic diagnosis requires a high degree of clinical suspicion and targeted biopsies. This case illustrates multifocal involvement of the gastrointestinal tract, from the colon to the ileum, highlighting the key role of endoscopy and capsule endoscopy in diagnosis and staging. The patient is currently under Hematology follow-up and has initiated treatment with bendamustine and rituximab.