Long term outcomes of gastric mucosa-associated lymphoid tissue lymphoma treated with radiotherapy: A multi-center retrospective cohort study.

Gastric mucosa-associated lymphoid tissue (MALT) lymphoma is a rare disease. Radiotherapy remains an important definitive modality. We assessed the long term outcomes of patients with early stage gastric MALT marginal zone lymphoma (MZL) treated with definitive radiotherapy at three institutions in New South Wales, Australia. A retrospective, multi-center study of patients with gastric MALT MZ lymphoma treated with radiotherapy between 1st of March 1999 and 31st of May 2020 was conducted. Eligible patients were: age ≥18 years, treated with curative-intent radiotherapy, pathological diagnosis of MALT MZ lymphoma. There were 33 eligible patients. Complete response (CR) was reported in 30/31 (96.7%) of endoscopically assessed cases. During median follow up of 66.2 months (IQR 22-119 months), estimated 5 and 10 years local relapse free survival were 92.6% (95% CI: 83-100) and 92.6% (95% CI: 83-100); distant relapse free survival 95.8% (95% CI 88.2-100) and 64.7% (95% CI 43.4-96.4); freedom from treatment failure 92.6% (95% CI; 83.1-100) and 62.5% (95% CI; 41.7-93.7), respectively. There were six documented recurrences; one local, four distant, and both in one patient; two cases were high grade recurrences. 5 and 10 years OS were 92.4% and 73.5% respectively. There were no grade 3-5 late toxicities or treatment related deaths. Patients with gastric MALT MZL treated with definitive radiotherapy have excellent outcomes. In long term follow up a significant proportion developed distant low grade disease. Extended follow up should be considered in these patients. Treatment is well tolerated with minimal toxicity. Radiotherapy remains an important modality in the treatment of gastric MALT MZ lymphoma.