Phase III randomised study of immunomodulatory therapy in high risk solitary bone plasmacytoma. IDRIS is a randomised, open label, multicentre phase III study. The aim is to investigate whether the administration of adjuvant lenalidomide and dexamethasone following standard radiotherapy treatment for SBP prevents or prolongs the time to development of further plasmacytomas or progression to myeloma, or death (whichever comes first), in patients with high-risk disease compared with RT only. Patients are risk-stratified following registration into the trial. Risk stratification is based on BM immunophenotyping and SFLC ratio. All patients will receive standard local radiotherapy; this is not regarded as trial treatment and may be administered prior to study entry.

• Patients with high-risk features will be randomised to receive adjuvant therapy in the form of lenalidomide and dexamethasone or no further treatment.
• Patients without high-risk features will receive no further therapy and will be observed according to local practice. 140 patients:
• 98 patients with high risk features to be randomised at a 1:1 ratio
• 42 low risk patients for registration only