Not the presence but the amount of clonal DNA detectable in remission of acute myeloid leukemia is predictive for relapse

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Abstract
Objectives: The persistence of clonal cells after chemotherapy, or a re‐emerging of clonal cells in remission (CR) or at relapse in patients with acute myeloid leukemia (AML) was studied to assess the prognostic significance of the amount of clonal DNA in predicting the clinical outcome. Methods: Clonal rearrangements in the gene sequences of retinoic acid receptor (RAR) α, major breakpoint cluster region (M‐bcr), immunoglobulin (Ig)‐JH, T‐cell receptor (TcR) β, myeloid lymphoid leukemia or cytokines (GM‐CSF, G‐CSF, IL‐3) detected in bone marrow samples from 37 patients with primary AML (pAML) or secondary AML (sAML) were investigated. A relative increase or decrease of clonal DNA in the course of AML was evaluated by comparing the optical densities of DNA bands of the rearranged genes and the total amount of DNA. Results: High amounts of clonal DNA were detectable at diagnosis, during persisting disease and at relapse (Ø 39%, 35%, or 38% of total DNA, respectively), compared to 20% in complete remission (CR). Amounts of clonal DNA (except for Ig‐JH gene rearrangements) were of prognostic significance at diagnosis, patients with less than 33% clonal DNA were characterized by significantly longer relapse‐free survival times (all cases: p = 0.01; pAML: p = 0.002). Patients in CR exhibiting less than 5% (all cases) or 15% (pAML) clonal DNA showed longer relapse‐free survival times (p = 0.08 or p = 0.03, respectively). Vice versa, significantly higher amounts of clonal DNA (all cases 51% vs. pAML 54%) could be detected in cases studied at diagnosis who relapsed in the following 5 months (all cases p = 0.01) or 14 months (pAML p = 0.007). Significantly higher amounts of clonal DNA (33%) could be detected in cases studied in CR who relapsed in the following 4 months (all cases p = 0.002 or pAML p = 0.006, respectively). Moreover, we could prove disease progression on a cellular level months before the clinical onset of sAML after a period of MDS. Conclusions: Clonal, gene‐rearranged DNA is regularly detectable at diagnosis and during persisting AML, in CR and at relapse. However, the presence, rather than the amount of clonal DNA detectable in CR is predictive for relapse. These data might indicate the significance of gene rearrangement analyses in the course of AML to identify cases with a high risk of relapse, independently from the karyotype.