Persistence of Minimal Residual Disease Assessed By Multi-Parameter Flow Cytometry Is a Strong Predictor of Outcome in Younger Patients with Acute Myeloid Leukemia

Background - Minimal Residual Disease (MRD) assessed by Multi-parameter Flow Cytometry (MFC) has not been extensively evaluated as a predictor of outcome in younger patients with acute myeloid leukemia (AML) receiving ara-C plus anthracycline induction

Methods - We examined the predictive value of MRD assessment by MFC in mainly younger patients with newly diagnosed AML who were treated with intermediate dose cytarabine (total of ≥ 6 g/m²) and idarubicin based induction chemotherapy. Among 280 patients treated with clofarabine, idarubicin plus ara-C (CIA), fludarabine, idarubicin plus ara-C (FIA), fludarabine, ara-C, GCSF plus idarubicin (FLAG-Ida), cladribine, idarubicin, plus ara-C (CLIA) who achieved complete remission (CR), CR without platelet recovery (CRp), or CR with incomplete count recovery (CRi) 186 had at least one available MRD data and are the subject of this analysis. MRD by MFC was assessed using an 8-color panel containing 19 distinct markers, on bone marrow specimens obtained at the time of achievement of CR/CRi/CRp (approximately 1-2 months post induction), during consolidation (approximately 3-7 months post-induction) and at completion of therapy (≥ 8 months post induction). Residual leukemic blasts were identified based on phenotypic differences from normal myelomonocytic precursors. Sensitivity was estimated at 0.1% in most cases, with maximum achievable sensitivity of 0.01%, depending on the leukemic phenotype.

Results - Median age of the patients was 51 years (Range, 17 - 77 years). 6 patients were older than 65 (all with ELN favorable disease). Median WBC at presentation was 4.7 x 10⁹/L (Range, 0.5 - 103 x 10⁹/L). Cytogenetics was favorable risk in 34 (18%), intermediate risk in 115 (62%) and adverse in 27 (15%) and was not available in 10 (5%) Treatment included CIA in 102 (55%), FIA in 34 (18%), FLAG-Ida in 34 (18%) and CLIA in 16 (9%). 166 patients had available samples at 1-2 months post induction and 131 (79%) became MRD negative. Achieving MRD negative status at response was associated with a statistically significant improvement in relapse free survival (RFS) (p= 0.001) and overall survival (OS) (p= 0.003) (Figure 1). 116 patients were evaluated for MRD status during consolidation and 100 (86%) became negative. Achieving a negative MRD status during consolidation was associated with a significant improvement in RFS (p˂0.001) and OS (p˂0.001)(Figure 2). 69 patients were evaluated for MRD status after completion of all therapy and 58 (84%) became negative. Achieving a negative MRD status at completion of therapy was associated with improvement in RFS (P˂0.001) and OS (P˂0.001) (Figure 3). On multivariate analysis including age ˂40 years vs. ≥ 40, WBC at presentation ˂or ≥ 10 x 10⁹/L, cytogenetics (favorable, intermediate, adverse), achieving CR vs. CRp/CRi, and treatment with CIA, FIA, CLIA, or FLAG-Ida, achieving MRD negative status was the only independent predictor of RFS and OS at response (P=0.03 and P=0.005, respectively), during consolidation (p˂0.001 for both), or at completion of therapy (p˂0.001 for both).

Conclusion - Achieving MRD negative status by MFC at response, during consolidation therapy and after completion of therapy is associated with a highly significant improvement in the outcome of younger patients with AML receiving ara-C plus idarubicin-based regimens.

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