Transformed gastric mucosa-associated lymphoid tissue lymphoma originating in the colon and developing metachronously after Helicobacter pylori eradication: A case report.

Background: Helicobacter pylori (H. pylori) eradication treatment for primary gastric mucosa-associated lymphoid tissue (MALT) lymphoma has already been established. However, t (11;18) (q21;q21)/API2-MALT1 translocation-positive lesions are a type of primary gastric MALT lymphoma in which a response to eradication treatment is difficult to achieve. In addition, trisomy 18 may be associated with diffuse large B-cell lymphoma (DLBCL) transformation of gastric MALT lymphoma.

Case summary: A 66-year-old man was diagnosed with MALT lymphoma in the ascending colon by colonoscopy and biopsy. Two years later, esophagogastroduodenoscopy revealed chronic atrophic gastritis that was positive for H. pylori, and eradication treatment was administered. Two years and nine months later (at the age of 70), a new ulcerative lesion suggestive of MALT lymphoma appeared in the gastric body, and six months later, a similar lesion was also found in the fundus. One year later (4 years and 3 months after H. pylori eradication), at the age of 72, the lesion in the gastric body had become deeper and had propagated. A biopsy revealed a pathological diagnosis of DLBCL. Both MALT lymphoma lesions in the ascending colon and DLBCL lesions in the stomach were positive for the t (11;18) (q21;q21)/API2-MALT1 translocation, and trisomy 18q21 was also detected. After 6 courses of R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine and prednisone) chemotherapy, all of the above lesions disappeared [complete remission (CR)], and CR has been maintained for more than 3 years. In addition, both the colonic and gastric lesions were proven to have the same clonality.

Conclusion: Because the patient had a MALT1 translocation with trisomy 18q21, it was thought that this gastric MALT lymphoma developed independently of H. pylori infection and progressed.