Prognostic Analysis of Colorectal Extranodal Marginal Zone Lymphoma of MALT Type: Clinical Outcomes and Implications

Introduction: Extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue type (MALToma) is a clonal B-cell neoplasm that arises in various organs, mainly in the stomach (60-70%), lung (15%), ocular adnexa (10%), salivary glands and thyroid, but rarely in the colorectum. MALToma generally exhibits an indolent course, typically remaining localized to the primary site for extended periods and often associated with a favorable prognosis. Nonetheless, there is a potential for recurrence or transformation into aggressive B-cell lymphoma. While there has been extensive research on gastric MALToma, colorectal MALToma is relatively rare, and its clinical characteristics and treatment outcomes are not yet clearly established. Methods: A retrospective analysis was conducted on patients newly diagnosed with colorectal MALToma at Asan Medical Center, Seoul, South Korea, between January 2007 and April 2023, to evaluate clinical characteristics and survival outcomes, including progression-free survival (PFS) and overall survival (OS). Results: A total of 83 consecutive patients were included. The median age was 60 years (range, 38-83) and 38 patients (45.8%) were male. Sixty-six patients (79.5%) were asymptomatic. Sixty-two patients (74.7%) had an International Prognostic Index (IPI) score of 1 or lower. According to the Ann Arbor staging system, 20 patients (24.1%) were classified as stage 4. Of the 53 patients who underwent bone marrow examination, 6 showed bone marrow involvement. The disease was most located in the rectum (n = 36, 43.4%), followed by the sigmoid colon (n = 13, 15.7%), transverse colon (n = 8, 9.6%), cecum (n = 7, 8.4%), ascending colon (n = 5, 6.0%), and descending colon (n = 4, 4.8%). Additionally, 10 patients (12.0%) had multiple lesions within the colorectum, and 5 patients (6.0%) were concurrently diagnosed with gastric MALToma. Forty-eight patients (57.8%) underwent endoscopic excision, 9 (10.8%) underwent surgical resection, 18 (21.7%) received radiotherapy, 11 (13.3%) received Helicobacter pylori eradication therapy, and 3 (3.6%) received systemic chemotherapy. Five patients (6.0%) were followed up without specific treatment. Among those who underwent endoscopic resection, 28 patients (58.3%) achieved complete resection, while 8 out of 9 patients (88.9%) who underwent surgical resection achieved complete resection. During the follow-up period, none developed transformation to aggressive lymphoma but a total of 6 patients died. Of these, 5 deaths were due to causes unrelated to MALToma, and the cause of death for 1 patient was not determined. Thus, with a median follow-up of 76.9 months, the 5-year PFS was 80.5% (95% CI, 71.3-90.8), and the 5-year OS rate was 97.1% (95% Confidence Interval [CI], 93.2-100.0). Of the 11 patients who experienced disease progression, 10 had locoregional progression, and only 1 developed distant lesions. Among these, only the patient with distant relapse exhibited the second progression. The following factors were not associated with PFS; location (confined to the rectum vs. other locations, p = 0.58) (right colon vs. left colon vs. both, p = 0.97), radiotherapy (p = 0.95), H. pylori eradication therapy (p = 0.16) and endoscopic or surgical resection (p = 0.28). Notably, two of the three patients who received chemotherapy experienced recurrence, suggesting that chemotherapy might have a limited role in disease control. Conclusions: Colorectal MALToma generally demonstrates a favorable prognosis with observation or either endoscopic or surgical resection, while significant benefits from systemic therapy was not evident.