Effect of lenalidomide treatment on clonal architecture of myelodysplastic syndromes without 5q deletion

Non-del(5q) transfusion-dependent low/intermediate-1 myelodysplasticsyndrome (MDS) patients achieve an erythroid response with lenalidomide in 25% of cases. Addition of an erythropoiesis-stimulating agent could improve response rate. The impact of recurrent somatic mutations identified in the diseased clone in response to lenalidomide and the drug's effects on clonal evolution remain unknown. We investigated recurrent mutations by next-generation sequencing in 94 non-del(5q) MDS patients randomized in the GFMLen- Epo-08 clinical trial to lenalidomide or lenalidomide plus epoetin b. Clonal evolution was analyzed after 4 cycles of treatment in 42 cases and reanalyzed at later time points in 18 cases. The fate of clonal architecture of single CD341CD382 hematopoietic stem cells was also determined in 5 cases. Mutation frequency was >10%: SF3B1 (74.5%), TET2 (45.7%), DNMT3A (20.2%), and ASXL1 (19.1%). Analysis of variant allele frequencies indicated a decrease of major mutations in 15 of 20 responders compared with 10 of 22 nonresponders after 4 cycles. The decrease in the variant allele frequency of major mutations was more significant in responders than in nonresponders (P < .001). Genotyping of single CD34⁺CD38^- cell-derived colonies showed that the decrease in the size of dominant subclones could be associated with the rise of founding clones or of hematopoietic stemcells devoid of recurrent mutations. These effects remained transient, and disease escape was associated with the re-emergence of the dominant subclones. In conclusion, we show that, although the drug initially modulates the distribution of subclones, loss of treatment efficacy coincides with the re-expansion of the dominant subclone. This trial was registered atwww.clinicaltrials.gov as #NCT01718379.