HemaSphere (Mar 2021)

Droplet Digital PCR Improves IG-/TR-based MRD Risk Definition in Childhood B-cell Precursor Acute Lymphoblastic Leukemia

  • Irene Della Starza,
  • Vittorio Nunes,
  • Federica Lovisa,
  • Daniela Silvestri,
  • Marzia Cavalli,
  • Andrea Garofalo,
  • Mimma Campeggio,
  • Lucia Anna De Novi,
  • Roberta Soscia,
  • Carlotta Oggioni,
  • Lara Mussolin,
  • Andrea Biondi,
  • Anna Guarini,
  • Maria Grazia Valsecchi,
  • Valentino Conter,
  • Alessandra Biffi,
  • Giuseppe Basso,
  • Robin Foà,
  • Giovanni Cazzaniga

DOI
https://doi.org/10.1097/HS9.0000000000000543
Journal volume & issue
Vol. 5, no. 3
p. e543

Abstract

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Minimal residual disease (MRD) is the most powerful prognostic factor in pediatric acute lymphoblastic leukemia (ALL). Real-time quantitative polymerase chain reaction (RQ-PCR) represents the gold standard for molecular MRD assessment and risk-based stratification of front-line treatment. In the protocols of the Italian Association of Pediatric Hematology and Oncology (AIEOP) and the Berlin-Frankfurth-Munschen (BFM) group AIEOP-BFM ALL2009 and ALL2017, B-lineage ALL patients with high RQ-PCR-MRD at day+33 and positive at day+78 are defined slow early responders (SERs). Based on results of the AIEOP-BFM ALL2000 study, these patients are treated as high-risk also when positive MRD signal at day +78 is below the lower limit of quantification of RQ-PCR (“positive not-quantifiable,” POS-NQ). To assess whether droplet digital polymerase chain reaction (ddPCR) could improve patients’ risk definition, we analyzed MRD in 209 pediatric B-lineage ALL cases classified by RQ-PCR as POS-NQ and/or negative (NEG) at days +33 and/or +78 in the AIEOP-BFM ALL2000 trial. ddPCR MRD analysis was performed on 45 samples collected at day +78 from SER patients, who had RQ-PCR MRD ≥ 5.0 × 10–4 at day+33 and POS-NQ at day+78 and were treated as medium risk (MR). The analysis identified 13 of 45 positive quantifiable cases. Most relapses occurred in this patients’ subgroup, while ddPCR NEG or ddPCR-POS-NQ patients had a significantly better outcome (P < 0.001). Overall, in 112 MR cases and 52 standard-risk patients, MRD negativity and POS-NQ were confirmed by the ddPCR analysis except for a minority of cases, for whom no differences in outcome were registered. These data indicate that ddPCR is more accurate than RQ-PCR in the measurement of MRD, particularly in late follow-up time points, and may thus allow improving patients’ stratification in ALL protocols.