Colonic mucosa-associated lymphoid tissue (MALT) lymphoma: an important differential diagnosis for a slow-growing colonic polyp

A 67-year-old man came to the gastroenterology clinic in 2013 for follow-up of a slow-growing asymptomatic colonic polyp. The polyp was first found on screening colonoscopy in 2006. It was smooth, sessile, 2 cm in size, and located in the transverse colon ([Fig. 1]). Histopathology results from the biopsy showed dense infiltrates of CD20 + lymphocytes within the lamina propria and a diagnosis of low grade extranodal mucosa-associated lymphoid tissue (MALT) lymphoma was made. The abdominal positron emission tomography-computed tomography (PET-CT) scan was unremarkable. Helicobacter pylori IgG antibody testing was equivocal and a 2-week course of ampicillin, clarithromycin, and esomeprazole was administered. Surveillance colonoscopy in 2007 showed the MALToma to be 3 cm in size. Because of its growing size, the patient was treated with four cycles of rituximab. Follow-up colonoscopy in 2010 showed that the mass had grown to 4 cm in size. A repeat PET-CT scan in 2012 was unremarkable. Colonoscopy in 2013 showed the mass to be 5 cm in size with blood oozing from the surface ([Fig. 2]). A repeat biopsy showed diffuse infiltration of the mucosa with lymphoid cells positive for CD20, CD79a and bcl2. Because of the increasing size and mucosal friability, laparoscopic colonic resection was performed. The colonic margins were clear and three lymph nodes were involved. The pathology report confirmed the diagnosis of extranodal MALT lymphoma (stage 1E).

Fig. 1 Colonoscopy on a 62-year-old man in 2006 showing the smooth sessile polyp in the transverse colon.

Fig. 2 Colonoscopy in 2013 showing the 5-cm polyp with friable mucosa in the transverse colon.

Colonic MALTomas account for only 2.5 % of all MALTomas [1]. Such MALTomas do not have a strong association with H. pylori infection and may not respond to H. pylori treatment [2] [3] [4] [5]. They should be managed as non-Hodgkin lymphoma by experienced oncologists. In conclusion, MALToma should be considered in the differential diagnosis of large polyps with a non-pitting surface or ulceration, or of polyps with ill-defined borders seen during screening colonoscopy.

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Competing interests: None

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