B-cell acute lymphoblastic leukemia in patients with chronic lymphocytic leukemia treated with lenalidomide

Abstract The placebo controlled CLLM1 trial evaluated the efficacy of lenalidomide maintenance treatment in patients with high-risk chronic lymphocytic leukemia (CLL) in first remission after chemoimmunotherapy (CIT). Upon observation of three cases with acute lymphoblastic leukemia (ALL) in overall 56 lenalidomide treated patients (5.4%), the study treatment was prematurely stopped. Using next generation sequencing of B cell and T cell receptor (TR) rearrangements, we here report common clonal B cell ancestry between CLL and ALL in one of those three patients, in whom both diseases shared the same VDJ- as well as crosslineage TR rearrangements. Chromosomal/mutation analyses indicated that in this patient the ALL developed from a common B cell precursor which lacks genomic lesions acquired in the CLL subclone, but shares a BIRC3 frameshift deletion (p.L421fs*). In two cases we found independent IGH rearrangements indicating de novo ALL development from a different B cell clone. A retrospective cohort analysis of >1600 CLL patients treated with first-line CIT in previously reported phase 2-3 studies of the German CLL study group, yielded a significantly lower cumulative incidence of ALL at 12.6 cases/100,000 patient years, compared to 1345.5 cases/100,000 patient-years observed in the lenalidomide arm of the CLLM1 study. Given our results and increasing knowledge on the biological effects of lenalidomide in bone marrow precursor cells, we discuss the potential involvement of lenalidomide in the pathogenesis of ALL in CLL patients.