Access through your institution Buy or subscribe We thank Ho-Wan Ip and Chi-Chiu So for their comments1 on the recently published European Treatment and Outcome Study (EUTOS) recommendations

on monitoring deep molecular response in chronic myeloid leukemia (CML)2 and welcome discussion on how to improve and standardize molecular monitoring for CML. Their letter raises three

main issues as following: (i) Testing laboratories should define their limit of quantitation (LoQ) as defined by the Clinical and Laboratory Standards Institute (CLSI)3 as a crucial adjunct

to determination of limit of detection (LoD). Although we did not specifically discuss LoQ in our recommendations, we did cite the CLSI guidelines and fully agree with this suggestion. The

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REFERENCES * Ho-Wan IP, Chi-Chiu SO . Deep molecular response in chronic myelogenous leukemia: ensuring accuracy and consistency. _Leukemia_ 2015; 29: 1620–1621. Article  Google Scholar  *

Cross NC, White HE, Colomer D, Ehrencrona H, Foroni L, Gottardi E _et al_. Laboratory recommendations for scoring deep molecular responses following treatment for chronic myeloid leukemia.

_Leukemia_ 2015; 29: 999–1003. Article  CAS  Google Scholar  * CLSI _Evaluation of Detection Capability for Clinical Laboratory Measurement Procedures; Approved Guideline (EP17-A2)_, 2nd

edn. Clinical and Laboratory Standards Institute: Wayne, PA, USA, 2012. * Rousselot P, Charbonnier A, Cony-Makhoul P, Agape P, Nicolini FE, Varet B _et al_. Loss of major molecular response

as a trigger for restarting tyrosine kinase inhibitor therapy in patients with chronic-phase chronic myelogenous leukemia who have stopped imatinib after durable undetectable disease. _J

Clin Oncol_ 2014; 32: 424–430. Article  CAS  Google Scholar  * Branford S, Hughes T . Diagnosis and monitoring of chronic myeloid leukemia by qualitative and quantitative RT-PCR. _Methods

Mol Med_ 2006; 125: 69–92. CAS  PubMed  Google Scholar  Download references ACKNOWLEDGEMENTS This work was supported by the European LeukemiaNet via the ‘European Treatment and Outcome

Study’ for CML. EUTOS is funded by Novartis, but the comments in this letter and the previously published recommendations were developed, finalized and written entirely by the authors.

AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * Faculty of Medicine, University of Southampton, Southampton, UK N C P Cross * National Genetics Reference Laboratory (Wessex), Salisbury, UK N C

P Cross * Medizinische Klinik, Universitätsmedizin Mannheim, Mannheim, Germany M C Müller * Abteilung Hämatologie/Onkologie, Klinik für Innere Medizin II, Universitätsklinikum Jena, Jena,

Germany A Hochhaus Authors * N C P Cross View author publications You can also search for this author inPubMed Google Scholar * M C Müller View author publications You can also search for

this author inPubMed Google Scholar * A Hochhaus View author publications You can also search for this author inPubMed Google Scholar CORRESPONDING AUTHOR Correspondence to N C P Cross.

ETHICS DECLARATIONS COMPETING INTERESTS The authors declare no conflict of interest. RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Cross, N., Müller,

M. & Hochhaus, A. Response to Ho-Wan Ip and Chi-Chiu. _Leukemia_ 29, 1619 (2015). https://doi.org/10.1038/leu.2015.97 Download citation * Published: 22 May 2015 * Issue Date: July 2015 *

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