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Extranodal non-Hodgkin's lymphoma (NHL) is a rare entity, occurring most frequently in the gastrointestinal (GI) tract, representing 5 - 20% of all NHL, and 30 - 45% of extranodal NHL. Lesions can appear along the entire GI tract, with the stomach being the most frequent organ (60 - 75%). Primary duodenal lymphoma (PDL) is extremely rare, and there is currently no scientific evidence to support the best therapeutic approach. The information available in the literature is very scarce, consisting mainly of isolated case reports, and case series with small number of patients, mostly in the Eastern population. This study aimed to describe the experience of an external radiation therapy department in the treatment of patients with PDL.

We retrospectively reviewed electronic files and treatment plans of patients treated with radiotherapy for PDL, between January 2011 and December 2021. Oncological outcomes and toxicities were collected and described for each patient.

Eight patients (4 men, median age 58.5 years, range 31 to 66 years) were considered for analysis. The median follow-up time was 30.3 months (range 6 to 60 months). Half of the patients had stage Ann Arbor IE. In two patients, lymphoma was incidentally diagnosed during endoscopy. Otherwise, the most frequent circumstances of diagnosis were epigastric pain (n=3) and dyspepsia (n=2). None of the patients included in the study had B symptoms. The portion of the duodenum where lymphoma occurred most frequently was at the DI/DII transition (62.5 %). The most frequent histological subtype was follicular lymphoma (75%). Very low-dose radiotherapy (VLDRT), 4 Gy in two fractions, was performed in 75% of patients in combination with Rituximab. Before being observed at our department, one patient was proposed for the Watch and Wait (WW) strategy, having progressed after 3 years. One patient had nausea grade 2 during treatment (evaluated using the CTCAE v5.0), and there were no late toxicities reported. All patients had a complete response at endoscopic duodenal biopsies.  At the end of the study, all patients were alive without relapse or progression of the disease.

PDL is a rare disease, with an indolent course and a good prognosis, however rare cases of histological transformation may occur, mainly to diffuse large B cell lymphoma. There are no established therapeutic guidelines for optimal treatment. Despite the small size and heterogeneity of our sample, this retrospective observational study suggests that VLDRT with Rituximab provides a potential good local control with minimal toxicity for patients with PDL. A more conservative approach with a WW strategy could also be an appropriate and safe treatment option. There are no methods to predict prognosis or progression in PDL. Therefore, an appropriate long-term follow-up strategy is important in patients with PDL, especially those selected for the WW strategy.