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Keywords:

  • childhood ALL;
  • CRLF2 ;
  • prognosis

A subset of childhood B-cell precursor acute lymphoblastic leukaemia (BCP-ALL) patients have recently been found to harbour rearrangements of the cytokine receptor-like factor 2 gene (CRLF2) (Mullighan et al, 2009; Russell et al, 2009). A number of molecular lesions result in deregulated overexpression of CRLF2 (CRLF2-d); the two most common being interstitial deletions of the pseudoautosomal region PAR1 (Xp22/Yp11) that results in a P2RY8-CRLF2 fusion with CRLF2 expression driven by the P2RY8 promoter, or alternatively, translocation of CRLF2 to the IGH@ locus (14q32) leading to deregulated CRLF2 expression via IGH@ enhancer elements – IGH@-CRLF2 (Mullighan et al, 2009; Russell et al, 2009). CLRF2-d has been reported in 5–15% of childhood and adult BCP-ALL (Haslam et al, 2011; Mullighan et al, 2009; Russell et al, 2009) and is particularly more frequent in Down Syndrome (DS)-ALL patients, where its presence is associated with mutations of JAK2, postulated to cooperate in propagating the leukaemia in such instances (Harvey et al, 2010; Chen , et al 2012). The prognostic significance of this abnormality remains unclear in childhood BCP-ALL with studies assigning CRLF2-d as either an adverse- or intermediate-risk prognostic factor (Cario et al, 2010; Palmi et al, 2012; Ensor et al, 2011; Harvey et al, 2010). The aim of our study was to determine the incidence and prognostic impact of CRLF2-d in diagnostic material from normal karyotype BCP-ALL patients treated according to the UK ALL 2003 protocol (ClinicalTrials.gov NCT00222612).

Forty-two patients were selected from the total cohort of 238 children diagnosed with BCP-ALL and treated with UK ALL 2003 protocol between 2004 and 2010 in our institution. The selection process was based on the availability of a good quality stored diagnostic bone marrow sample for patients with intermediate cytogenetic risk, as defined by absence of the following: high hyperdiploid karyotype (chromosome N > 50), recognized translocations (ETV6-RUNX1, BCR-ABL1, MLL-AFF1 and IGH@-MYC) and constitutional trisomy 21 (DS). Cytogenetic and fluorescence in situ hybridization (FISH) data were available for all patients. CRLF2 over-expression was determined by real-time quantitative polymerase chain reaction (RQ-PCR) with underlying genomic rearrangements detected by either reverse transcription polymerase chain reaction (RT-PCR) (P2RY8-CRLF2 fusion transcripts) or FISH (break-apart IGH@; Abbott Laboratories, Abbott Park, IL, USA) as previously described (Haslam et al, 2011). Data were correlated with clinical risk factors, minimal residual disease (MRD) status and clinical outcome and analysed using Statistica (Statsoft, Milton Keynes, UK). The parents or guardians consented according to the Declaration of Helsinki for all participants.

Overall, eight out of 42 patients (19%) were positive for the P2RY8-CRLF2 fusion, four of whom had high CRLF2 over-expression. No IGH@ translocations were detected. There was no significant difference in National Cancer Institute (NCI) risk status between CRLF2-d and non-CRLF2-d groups, although there was a tendency for lower blast cell count at presentation (10·0 vs. 39·0, P = 0·3) in the CRLF2-d group. No statistical significance was observed between day-28 MRD status and CRLF2-d. Four relapses were observed (two non-CRLF2-d (5·8%) and two CRLF2-d (25%). No statistical difference in overall and progression-free survival (PFS) was observed (PFS, 93·2% non-CRLF2-d versus 86% CRLF2-d, P = 0·11). There was also no clinical or laboratory differences between those patients with high and low CRLF2 expression.

Genomic alterations of CRLF2 are emerging as additional high-risk molecular/cytogenetic features in some childhood ALL treatment trials. As reported by Attarbaschi et al (2012), we too did not observe a higher relapse-risk associated with the P2RY8-CRLF2 fusion regardless of any association with high levels of CLRF2 expression, suggesting that these patients are most likely to be of intermediate protocol-independent risk and therefore should not be considered at the present time for more intensive therapy. Given the deficiencies of our study, namely; small sample size and retrospective design, a larger study using multiple regression analysis would be needed to confirm the true prognostic impact of CRLF2-d in BCP-ALL. In addition, further assessment is required to define the underlying molecular mechanisms responsible for the absence of high CRLF2 expression in those patients with a P2RY8-CRLF2 translocation. Future risk algorithms are needed that will incorporate CRLF2-d status in prospective clinical trials in order to determine its true prognostic significance, as well as the potential therapeutic role of JAK2 and phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) inhibitors (Tasian et al, 2012).

Author contributions

  1. Top of page
  2. Author contributions
  3. Conflict of interest
  4. References

J.K, L.S., A.O'M. and O.P.S provided patient care and clinical information; K.H. and S.E.L. performed molecular studies; P.L. provided study samples; J.K performed cytogenetic studies. All authors read and approved the final version of the manuscript.

Conflict of interest

  1. Top of page
  2. Author contributions
  3. Conflict of interest
  4. References

All authors disclose no conflicts of interest.

References

  1. Top of page
  2. Author contributions
  3. Conflict of interest
  4. References
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