Longer‐term follow‐up and outcome by tumour cell proliferation rate (Ki‐67) in patients with relapsed/refractory mantle cell lymphoma treated with lenalidomide on MCL‐001(EMERGE) pivotal trial

Patients with mantle cell lymphoma (MCL) generally respond to first-line immunochemotherapy, but often show chemoresistance upon subsequent relapses, with poor outcome. Several studies of the immunomodulator, lenalidomide, have demonstrated its activity in MCL including the MCL-001 study in relapsed/refractory patients who had failed defined prior therapies of anthracyclines or mitoxantrone, cyclophosphamide, rituximab and also bortezomib. We present here the long-term efficacy follow-up of the prospective phase II MCL-001 study (N = 134), including new exploratory analyses with baseline Ki-67 (MIB1), a biological marker of tumour proliferation. With longer follow-up, lenalidomide showed a 28% overall response rate [ORR; 8% complete response (CR)/CR unconfirmed (CRu)]. Median duration of response (DOR), progression-free survival and overall survival were 16·6, 4·0 and 20·9 months, respectively. Myelosuppression continued to be the most common grade 3/4 toxicity. Several studies of MCL patients treated with chemotherapy, rituximab and bortezomib have shown an inverse association between survival and Ki-67. Ki-67 data in 81/134 MCL-001 patients showed similar ORRs in both low (<30% or <50%) versus high (≥30% or ≥50%) Ki-67-expressing groups, yet lower Ki-67 levels demonstrated superior CR/CRu, DOR and survival outcomes. Overall, lenalidomide showed durable efficacy with a consistent safety profile in heavily pretreated, relapsed/refractory MCL post-bortezomib.