IELSG 37: a phase 3 trial to find out if radiotherapy can be safely omitted in people with primary mediastinal large B-cell lymphoma who are PET negative after chemotherapy

The aim of this trial is to find out if radiotherapy to the mediastinum (the centre of the chest) can be safely omitted in people with primary mediastinal large B-cell lymphoma (PMBL) who have had a good response to chemo-immunotherapy (chemotherapy and the antibody therapy rituximab).

Purpose of trial

Radiotherapy is usually given to reduce the risk of PMBL relapsing (coming back) but it can cause late effects (side effects that develop months or years after treatment), for example heart problems and second cancers.

Doctors want to find out whether a good response to chemo-immunotherapy on a PET/CT scan means you don’t need radiotherapy as well.


You can enter the study before, or up to 4 weeks after, starting chemo-immunotherapy. Your doctor can choose what chemo-immunotherapy regimen they think is best for you.

Before or shortly after you start treatment, you have a PET/CT scan. When you have finished treatment, you have another PET/CT scan to see if your lymphoma has responded to treatment.

If you are PET negative, this means you are in complete remission (no evidence of lymphoma). You are then randomised to decide whether or not you receive radiotherapy. If you are randomised to receive radiotherapy, you have it for 2-3 weeks after your chemo-immunotherapy.

If you don’t respond well to your chemo-immunotherapy (PET positive), your doctor decides what further treatment you need. You are still followed-up for 10 years as part of the study to see how you are doing.

Who can enter

Your consultant can give you advice on whether this trial might be suitable for you.

Around 540 people are needed for this trial.

You may be able to enter if:

  • You have primary mediastinal large B-cell lymphoma that has CD20 protein on the lymphoma cells. This is confirmed from your biopsy .
  • You don’t have any extranodal (outside the lymph nodes) lymphoma outside of your chest.
  • You haven’t had treatment yet but are planned to have chemotherapy and rituximab with the aim of curing your lymphoma.
  • Your treatment plan includes at least 6 cycles of rituximab.
  • You and your partner are willing to use reliable contraception if there is any chance of you or your partner becoming pregnant.
  • You are 18 or over.

You will not be able to enter if:

  • You’ve had a previous cancer in the last 5 years, unless it was certain localised cancers.
  • You have significant heart problems.
  • You are HIV positive.
  • You are pregnant or breastfeeding.

Further information

More information about this trial is available at