Prognostic Significance of Minimal Residual Disease in Adult Patients with B-Lineage Acute Lymphoblastic Leukemia by 8-Color Flow Cytometry

Abstract 4789

Monitoring of minimal residual disease (MRD) in patients with acute lymphoblastic leukemia (ALL) by immunophenotyping and/or molecular techniques provides a way to precisely evaluate early treatment response and predict relapse. In this study, we have investigated the prognostic significance of MRD in adult patients with B-lineage acute lymphoblastic leukemia (B-ALL) by 8-color flow cytometry. A cohort of 106 patients with B-ALL who had achieved a complete remission (CR) and at least 1 LAIP characteristics were enrolled to perform MRD assessment at the end of induction and 1 cycle of consolidation. LAIPs were identifiable in 96% of the patients by 8-color flow cytometric assay, in which, most cases (90.6%) containing 2 or more LAIPs had a sensitivity as high as identifying 1 leukemic blast among 1×10⁵ BM nucleated cells. MRD negative status could clearly predict a favorable 1 year relapse free survival (RFS) and 2 year overall survival (OS) when a cut-off level of 0.01% was used to define MRD positivity at the point of achieving CR (P=0.000 and 0.000, respectively) and after 1 cycle of consolidation (P=0.000 and 0.000, respectively), respectively. In multivariate analysis including cytogenetic abnormalities, clinical factors and MRD status, late CR (P=0.046), MRD status at the points of obtaining CR (P=0.016) and 1 consolidation (P=0.007) were associated with RFS independently, while only MRD status after 1 course of consolidation was independent prognostic factor for OS (P=0.000). Of note, in exploring the fewer patients with MRD negative status experienced recent relapse, we have identified that most of such patients had a MRD level of 10⁻⁴−10⁻⁵ comparing to undetectable MRD level. Furthermore, our evidences showed that MRD assessed by flow cytometry and by RQ-PCR assay targeting to BCR-ABL fusion gene yielded concordant results in the vast majority of cases (90%). In conclusion, immunophenotypic evaluation of MRD by 8-color flow cytometry could work as an important tool to assess the treatment response and prognosis precisely in adult B-ALL.