• Simona Bernardi, Michele Malagola, Camilla Zanaglio, Nicola Polverelli, Elif Dereli Eke, Mariella D'Adda, Mirko Farina, Cristina Bucelli, Luigi Scaffidi, Eleonora Toffoletti, Clara Deambrogi, Fabio Stagno, Micaela Bergamaschi, Luca Franceschini, Elisabetta Abruzzese, Maria Domenica Divona, Marco Gobbi, Francesco Di Raimondo, Gianluca Gaidano, Mario Tiribelli, Massimiliano Bonifacio, Chiara Cattaneo, Alessandra Iurlo, and Domenico Russo.
• Unit of Blood Diseases and Stem Cell Transplantation, DPT of Clinical and Experimental Sciences, University of Brescia, ASST Spedali Civili di Brescia, Brescia, Italy.
• Cancer Med. 2019 May 1; 8 (5): 2041-2055.

AbstractTreatment-free remission (TFR) by tyrosine kinase inhibitors (TKI) discontinuation in patients with deep molecular response (DMR) is a paramount goal in the current chronic myeloid leukemia (CML) therapeutic strategy. The best DMR level by real-time quantitative PCR (RT-qPCR) for TKI discontinuation is still a matter of debate. To compare the accuracy of digital PCR (dPCR) and RT-qPCR for BCR-ABL1 transcript levels detection, 142 CML patients were monitored for a median time of 24 months. Digital PCR detected BCR-ABL1 transcripts in the RT-qPCR undetectable cases. The dPCR analysis of the samples, grouped by the MR classes, revealed a significant difference between MR4.0 and MR4.5 (P = 0.0104) or MR5.0 (P = 0.0032). The clinical and hematological characteristics of the patients grouped according to DMR classes (MR4.0 vs MR4.5-5.0 ) were superimposable. Conversely, patients with dPCR values <0.468 BCR-ABL1 copies/µL (as we previously described) showed a longer DMR duration (P = 0.0220) and mainly belonged to MR4.5-5.0 (P = 0.0442) classes compared to patients with higher dPCR values. Among the 142 patients, 111 (78%) discontinued the TKI treatment; among the 111 patients, 24 (22%) lost the MR3.0 or MR4.0 . RT-qPCR was not able to discriminate patients with higher risk of MR loss after discontinuation (P = 0.8100). On the contrary, according to dPCR, 12/25 (48%) patients with BCR-ABL1 values ≥0.468 and 12/86 (14%) patients with BCR-ABL1 values <0.468 lost DMR in this cohort, respectively (P = 0.0003). Treatment-free remission of patients who discontinued TKI with a dPCR <0.468 was significantly higher compared to patients with dPCR ≥ 0.468 (TFR at 2 years 83% vs 52% P = 0.0017, respectively). In conclusion, dPCR resulted in an improved recognition of stable DMR and of candidates to TKI discontinuation.© 2019 The Authors. Cancer Medicine published by John Wiley & Sons Ltd.

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