A 66-year-old male patient presented to the Department of Gastroenterology at Hallym University Sacred Heart Hospital for further evaluation and treatment of a colonic mass lesion, which was identified during a screening colonoscopy performed at a local clinic. His medical history included the removal of colonic polyps several years prior, and he was currently undergoing treatment for diabetes mellitus. Esophagogastroduodenoscopy at the local clinic revealed a poorly defined, flat-elevated subepithelial lesion with a discolored surface and prominent capillaries on the posterior wall of the antrum (Fig. 1A). A colonoscopy identified an approximately 3×2 cm globular-shaped subepithelial tumor covered with erythematous yet otherwise normal-appearing mucosa in the sigmoid colon (Fig. 1B). Initial gastric biopsy results indicated chronic gastritis with erosion and lymphoid aggregation without Helicobacter pylori infection, and the biopsy of the colonic lesion showed chronic active inflammation with erosion and dense lymphoid aggregation. Subsequent re-biopsy of the gastric lesion and endoscopic submucosal dissection (ESD) of the colonic lesion were performed in our institution (Fig. 2).

What is the most likely diagnosis?

Pathologic findings from the gastric biopsy revealed small lymphoid cell infiltration with occasional lymphoepithelial lesions. The colonic ESD specimen biopsy showed diffuse lamina propria infiltration by small lymphoid cells with frequent lymphoepithelial lesions (Fig. 2B and C). Immunohistochemical staining from colonic biopsy specimen revealed positivity for CD3, CD20, bcl2, and Ki-67 and negativity for bcl6 and Cyclin D1. Additional testing for Helicobacter pylori infection showed negative results in both the serology and urea breath test. There was no evidence of metastasis in the computed tomography scan. The final diagnosis was synchronous marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (MALT) of the stomach and colon, classified as stage II according to the Ann Arbor staging system. Since the patient has two primary lesions and selecting the radiation therapy field for the colonic mass was challenging, systemic chemotherapy was chosen following a detailed discussion with the patient. The patient underwent six cycles of chemotherapy with the CVP (cyclophosphamide, vincristine, prednisone) regimen, and no signs of recurrence were observed on follow-up endoscopy(Fig. 3). This case highlights the rare occurrence of synchronous MALT lymphoma in both the stomach and colon.

MALT lymphoma is a subtype of non-Hodgkin’s lymphoma characterized by low-grade malignancy originating from B cells [1,2]. It predominantly involves the gastrointestinal tract in 60%–70% of cases, while 30%–40% may occur in other locations, such as the salivary glands, conjunctiva, thyroid, eyes, lungs, pleura, kidneys, liver, and prostate [1,2]. Within the gastrointestinal tract, the stomach is the most common primary site, followed by lower incidences in the small intestine, cecum, colon, and esophagus [3]. Primary malignant lymphoma of the colon is relatively rare, comprising only 0.2%–0.65% of all malignant colonic tumors, with MALT lymphoma accounting for approximately 60% of these cases [4,5]. In the colon and rectum, MALT lymphoma typically presents as a solitary mass; however, synchronous MALT lymphoma in both the stomach and colon, as seen in this case, is exceedingly uncommon [6,7].

Localized MALT lymphoma in the colon can often be effectively managed with radical resection, with surgical intervention being the most common treatment strategy. Endoscopic polypectomy or ESD, as employed in this case, is also a valuable therapeutic option. MALT lymphoma generally demonstrates a slow progression, often remaining localized for extended periods without metastasis until reaching advanced stages [8,9]. Following treatment, the disease typically disseminates gradually, and long intervals before recurrence have been reported, underscoring the importance of timely intervention to achieve favorable clinical outcomes [10,11]. However, clinicians should remain vigilant for potential metastasis to other organs or lymph nodes at the time of diagnosis, as MALT lymphoma may recur at other sites even after localized treatment [10,11]. Therefore, comprehensive evaluations for multiple or metastatic occurrences at diagnosis are essential.

While synchronous MALT lymphoma in the stomach and colon is rare, this case underscores the importance of considering the possibility of such co-occurrence. We encountered a rare case of synchronous MALT lymphoma in both the stomach and colon, highlighting the need for a rigorous diagnostic approach. Early detection through advanced endoscopic techniques is critical for effective treatment and potential cure, particularly for localized cases of colonic MALT lymphoma.