Cumulative dose reduction (versus time on lenalidomide) because of toxicity in 17 of 72 patients. Patient 13 was dose-reduced to 15 mg lenalidomide because of grade 3 gastrointestinal toxicity. Patients 7 and 10 were dose-reduced to 15 mg lenalidomide because of grade 3 skin toxicity (rash). The remaining patients were dose-reduced because of myelosuppression according to the guidelines in Table S1. G-CSF indicates granulocyte colony-stimulating factor.