# IELSG37

Source: https://onco.cc/trials/ielsg37/  
OnCo record `ielsg37` (Trial). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

IELSG37 showed that people with primary mediastinal B-cell lymphoma whose scan is clear after chemotherapy do not need radiotherapy to the chest, sparing young patients decades of heart and breast cancer risk.

## Summary

IELSG37 registered 545 patients with primary mediastinal large B-cell lymphoma treated with rituximab-containing immunochemotherapy (mostly R-CHOP or dose-adjusted EPOCH-R, by centre) and randomised the 268 who reached a complete metabolic response on end-of-treatment PET (Deauville 1 to 3) to 30 Gy consolidation radiotherapy or to observation.

Progression-free survival at 30 months was 96.7 percent without radiotherapy and 98.5 percent with it, within the non-inferiority margin, with no difference in overall survival. Patients with residual PET uptake were not randomised and received radiotherapy, in whom outcomes were also good.

The trial settled a forty-year argument: mediastinal radiotherapy can be omitted in the majority of patients who reach complete metabolic response, and PET now decides who is irradiated.

## Fields

- Kind: Trial
- Status: positive
- Last checked: 2026-09-17
- Registry id: NCT01599559
- Phase: 3
- Setting: Primary mediastinal large B-cell lymphoma in complete metabolic response on PET after rituximab-based immunochemotherapy: consolidation mediastinal radiotherapy versus observation
- Sponsor: International Extranodal Lymphoma Study Group
- Enrolled: 545
- Result: 30-month progression-free survival 96.7% (observation) vs 98.5% (radiotherapy) in patients with complete metabolic response; radiotherapy can be omitted.
- Outcomes: Progression-free survival at 30 months: Observation 96.7% vs Consolidation radiotherapy 30 Gy 98.5%
- Replication: Consistent with the single-arm National Cancer Institute DA-EPOCH-R series, in which no patient received radiotherapy and event-free survival was 93 percent.

## Sources

- ClinicalTrials.gov NCT01599559: https://clinicaltrials.gov/study/NCT01599559
- Journal of Clinical Oncology 2024: https://doi.org/10.1200/JCO.24.01373

## Connected records

- cancers: [Primary mediastinal (thymic) large B-cell lymphoma](https://onco.cc/cancers/primary-mediastinal-b-cell-lymphoma/)
- technologies: [FDG PET](https://onco.cc/technologies/fdg-pet/), [IMRT / IGRT (modern external beam)](https://onco.cc/technologies/imrt-igrt/), [PET-adapted (response-adapted) therapy](https://onco.cc/technologies/pet-adapted-therapy/)
- drugs: [Rituximab](https://onco.cc/drugs/rituximab/)
- terms: [Deauville five-point scale](https://onco.cc/terms/deauville-score/), [Lugano classification / Ann Arbor staging](https://onco.cc/terms/lugano-classification/), [R-CHOP (lymphoma chemoimmunotherapy)](https://onco.cc/terms/r-chop/)

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