Molecular Monitoring of Residual Disease (MRD) during Induction and Intensification Phases in Low Risk Adult B Cell ALL Treated According to the MRC UKALL12 Protocol.

Introduction and aims. Molecular monitoring of minimal residual disease (MRD) using Immunoglobulin (IG) and T cell receptor (TCR) targets has provided an independent and prognostically significant parameter of outcome in adult and childhood acute lymphoblastic leukaemia (ALL). The aim of our study was to evaluate the impact of molecular tests carried out during the first 20 to 24 weeks of chemotherapy for MRD in a standard risk group of adult B cell ALL patients.

Patients and Methodology. We evaluated MRD tests in 63 patients with B cell ALL (37M/26F). Median age of our cohort was 24 yrs (range: 15.5–54.6 yrs) while median WBC was 9.9 (range: 1.1–553 × 10⁹l). All were negative for the t(9;22) or t(4;11) translocation and received standard induction chemotherapy or auto stem cell transplant (A-SCT) only. All patients had at least one molecular marker which was tested by quantitative or semi-quantitative PCR with sensitivity ≥1E4 and all tests were carried out at time of morphological remission. End-points were relapse or continuous clinical remission (CCR) with follow up ≥12 months. Time point for molecular evaluation were post induction phase 1, TP1 (up to 1.8 mo), post induction phase 2 (1.8–3.5 mo), post intensification (3.5–5.7 mo). Median follow up was 92 months for patients in CCR (range 12–141 mo) and 15.5 months for patients who relapsed (range: 2.4–49 mo).

Results. Thirty-five patients in complete morphological remission were tested at TP1. Relapse free survival (RFS) tests showed a statistically significant correlation (p=0.02) between MRD positive tests and relapse (n=19 pts) and MRD negative tests (n=16 pts) and relapse free survival. In addition, pts with resistant disease at TP1 (n=10; not included above) and MRD positive pts were indistinguishable as far as relapse FS and both faired extremely poorly (Figure A).

Thirty patients were analysed at TP2. RFS confirmed the significant association between MRD positivity and poor outcome (n=16 pts) and MRD negativity and CCR (n=14 pts) (p=0.03) (Figure B).

MRD data were also available for 43 patients at TP3. Association of MRD positive tests (n=15 pts) and MRD negative tests (n=28 pts) with poor and good outcome, respectively (p=0.0006) (Figure C) was strongest at this time point. Outcome correlated with level of MRD at all time points, with poorer outcome in patients with MRD >1E3.

Conclusions. Molecular monitoring during induction and intensification for standard risk B cell ALL patients treated with UKALL12 protocol provides a prognostically significant parameter for the management of adult ALL in otherwise morphological remission and may in the future be used for patients’ stratification.

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