Semen analysis and reproductive hormones in boys with classical Hodgkin lymphoma treated according to the EuroNet-PHL-C2 protocol.

STUDY QUESTION: What is the impact of the EuroNet-PHL-C2 treatment for boys with classical Hodgkin lymphoma (cHL) on semen parameters? SUMMARY ANSWER: More than half of the patients (52%, n = 16/31) had oligozoospermia or azoospermia at 2 years from cHL diagnosis; particularly boys treated for advanced-stage cHL had low sperm counts and motility. WHAT IS KNOWN ALREADY: Chemotherapy and radiotherapy to the inguinal region or testes can impair spermatogenesis and result in reduced fertility. The EuroNet-PHL-C2 trial aims to minimize radiotherapy in standard childhood cHL treatment, by intensifying chemotherapy. The present study aims to assess the (gonadotoxic) impact of this treatment protocol on semen parameters and reproductive hormones in boys aged ≤18 years. STUDY DESIGN, SIZE, DURATION: This international, prospective, multi-centre cohort study was an add-on study to the randomized phase-3 EuroNet-PHL-C2 trial, where the efficacy of standard cHL treatment with OEPA-COPDAC-28 (OEPA: vincristine, etoposide, prednisone, and doxorubicin; COPDAC-28: cyclophosphamide, vincristine, prednisone, and dacarbazine) was compared to intensified OEPA-DECOPDAC-21 chemotherapy (DECOPDAC-21: COPDAC with additional doxorubicin and etoposide and 25% more cyclophosphamide). Patients were recruited between January 2017 and September 2021. PARTICIPANTS/MATERIALS, SETTING, METHODS: Eligibility criteria included male patients, diagnosed with classical HL before or at the age of 18 years, and treated according to the EuroNet-PHL-C2 protocol in any of the 18 participating sites in the Netherlands, Germany, Belgium, Czech Republic, and Austria. Sperm parameters (sperm concentration, progressive motility, sperm volume, and calculated total motile sperm count) were assessed at diagnosis and 2 years after diagnosis in (post)pubertal boys. Laboratory measurements (serum follicle-stimulating hormone (FSH) and inhibin B) were performed in samples drawn at diagnosis, during treatment (2-3 times), and at 2 years post-diagnosis, and (age-adjusted) analyses were conducted separately for pre-pubertal and (post)pubertal boys. Outcomes were compared between the treatment levels (TL1, TL2, and TL3) and consolidation treatment schemes (COPDAC-28 and DECOPDAC-21). MAIN RESULTS AND THE ROLE OF CHANCE: In total, 101 boys were included in the present analysis: 73 were (post)pubertal (median age 15.4 years, (IQR 14.4; 16.6), 10 TL1, 29 TL2, 34 TL3, 62% of TL2/3 patients received COPDAC-28) and 28 boys were pre-pubertal (median age 9.6 years (IQR 6.6; 11.4), 4 TL1, 7 TL2, 17 TL3, 38% of TL2/3 patients received COPDAC-28). The study included six boys who had received pelvic radiotherapy; none were irradiated in the inguinal or testicular area. At diagnosis, 48 (post)pubertal boys delivered semen for cryopreservation; 19 (40%) semen samples were oligospermic and 4 (8%) were azoospermic. Low sperm concentration (<15 mil/ml) appeared to be related to the HL disease itself, with a higher prevalence in boys who presented with B symptoms (76% vs 26%, aOR 2.3 (95% CI 1.0; 3.8), P = 0.001) compared to those without such symptoms. At 2 -years post-diagnosis, 31 boys provided semen samples for analysis, of whom 12 (39%) boys had oligozoospermia and 4 (13%) had azoospermia, while 22 boys (71%) had low total motile sperm counts (TMSC) (<20 mil). Specifically, the eight boys in the TL3 group treated with DECOPDAC-21 consolidation had low sperm counts and low progressive motility after 2 years (i.e. median sperm count 1.4 mil/ml (IQR <0.1; 5.3), n = 7 (88%), low sperm concentration, low median progressive motility 16.5% (IQR 0.0; 51.2), respectively). Age-adjusted serum FSH levels were significantly raised and inhibin B levels (and inhibin B:FSH ratios) were decreased during chemotherapy in (post)pubertal boys, with subsequent normalization in 80% (for FSH) and 60% (for inhibin B) of boys after 2 years. Only 4 out of the 14 (post)pubertal boys (29%) with low sperm concentrations after 2 years had elevated FSH (>7.6 IU/l), while 7 (50%) had low inhibin B levels (<100 ng/l). In pre-pubertal boys, reproductive hormones were low overall and remained relatively stable during chemotherapy. LIMITATIONS, REASONS FOR CAUTION: The present analyses included sperm and laboratory measurements up to 2 years post-diagnosis. Long-term reproductive outcomes and potential recovery of spermatogenesis remain unknown, while recovery was reported up to 5- or even 10-year post-chemotherapy in previous studies.Boys who were pre-pubertal at diagnosis were still too young and/or physically not able to deliver semen after 2 years and we could not assess a potential difference in gonadotoxicity according to pubertal state at the time of treatment. Overall, the statistical power of the analyses on sperm concentration and quality after 2 years was limited. WIDER IMPLICATIONS OF THE FINDINGS: Results of the semen analyses conducted among the 31 boys who had provided a semen sample at 2 years post-treatment were generally poor. However, additional long-term and adequately powered data are crucial to assess the potential recovery and clinical impact on fertility. The participating boys will be invited to deliver a semen sample after 5 years. Until these data become available, benefits of intensified chemotherapy in cHL treatment to reduce radiotherapy and lower risk for development of secondary tumours should be carefully weighed against potentially increased risk of other late effects, such as diminished fertility due to the increased chemotherapy burden. Boys with newly diagnosed cHL should be encouraged to deliver sperm for cryopreservation whenever possible. However, patients and clinicians should also realize that the overall state of disease and inflammatory milieu of cHL can negatively affect sperm quality and thereby reduce chance of successful fertility preservation. Furthermore, the measurement of FSH and inhibin B appears to be of low value in predicting low sperm quality at two years from cHL treatment. STUDY FUNDING/COMPETING INTEREST(S): This study was funded by the Dutch charity foundation KiKa (project 257) that funds research on all forms of childhood cancer. C.M.-K., D.K., W.H.W., D.H., MC, A.U., and A.B. were involved in the development of the EuroNet-PHL-C2 regimen. The other authors declare no potential conflict of interest. TRIAL REGISTRATION NUMBER: N/A.

The impact of treatment for childhood classical Hodgkin lymphoma according to the EuroNet-PHL-C2 protocol on serum anti-Müllerian Hormone.

STUDY QUESTION: What is the impact of the EuroNet-PHL-C2 treatment protocol for children with classical Hodgkin lymphoma (cHL) on gonadal function in girls, based on assessment of serum anti-Müllerian hormone (AMH)? SUMMARY ANSWER: Serum AMH levels decreased after induction chemotherapy and increased during subsequent treatment and 2 years of follow-up, with lowest levels in patients treated for advanced stage cHL. WHAT IS KNOWN ALREADY: Treatment for cHL, particularly alkylating agents and pelvic irradiation, can be gonadotoxic and result in premature reduction of primordial follicles in females. The current EuroNet-PHL-C2 trial aims to reduce the use of radiotherapy in standard childhood cHL treatment, by intensifying chemotherapy. This study aims to assess the gonadotoxic effect of the EuroNet-PHL-C2 protocol. STUDY DESIGN, SIZE, DURATION: This international, prospective, multicenter cohort study is embedded in the EuroNet-PHL-C2 trial, an European phase-3 treatment study evaluating the efficacy of standard cHL treatment with OEPA-COPDAC-28 (OEPA: vincristine, etoposide, prednisone, and doxorubicin; COPDAC-28: cyclophosphamide, vincristine, prednisone, and dacarbazine) versus intensified OEPA-DECOPDAC-21 (DECOPDAC-21: COPDAC with additional doxorubicin and etoposide and 25% more cyclophosphamide) in a randomized setting. Participants were recruited between January 2017 and September 2021. PARTICIPANTS/MATERIALS, SETTING, METHODS: Female patients aged ≤18 years, treated according to the EuroNet-PHL-C2 protocol for cHL were recruited across 18 sites in the Netherlands, Belgium, Germany, Austria, and Czech Republic. All parents and patients (aged ≥12 years old) provided written informed consent. Serum AMH levels and menstrual cycle characteristics were evaluated over time (at diagnosis, one to three times during treatment and 2 up to 5 years post-diagnosis) and compared between treatment-levels (TL1, TL2, and TL3) and treatment-arms (OEPA-COPDAC-28 and OEPA-DECOPDAC-21). Serum samples obtained from patients after receiving pelvic radiotherapy were excluded from the main analyses. MAIN RESULTS AND THE ROLE OF CHANCE: A total of 104 females, with median age at diagnosis of 15.6 years (IQR 13.7; 17.0), were included in the analysis. Ninety-nine were (post)pubertal. Eighteen girls were diagnosed with an early stage of cHL (TL1) and 86 with intermediate or advanced stage disease (50 TL2 and 36 TL3, 66% received COPDAC-28 and 34% DECOPDAC-21). Five patients received pelvic radiotherapy. Median AMH level at diagnosis was 1.7 µg/l (IQR 0.9; 2.7). After two courses of OEPA chemotherapy, AMH levels decreased substantially in all patients (98% <0.5 µg/l), followed by a significant increase during the consolidation treatment and follow-up. After 2 years, 68% of patients reached their baseline AMH value, with overall median recovery of 129% (IQR 75.0; 208.9) compared to baseline measurement. Five patients (7%) had AMH <0.5 µg/l. In patients treated for advanced stage disease, AMH levels remained significantly lower compared to early- or intermediate stage disease, with median serum AMH of 1.3 µg/l (IQR 0.8; 2.1) after 2 years. Patients who received DECOPDAC-21 consolidation had lower AMH levels during treatment than patients receiving COPDAC-28, but the difference was no longer statistically significant at 2 years post-diagnosis. Of the 35 postmenarchal girls who did not receive hormonal co-treatment, 19 (54%) experienced treatment-induced amenorrhea, two girls had persisting amenorrhea after 2 years. LIMITATIONS, REASONS FOR CAUTION: The studied population comprises young girls with diagnosis of cHL often concurring with pubertal transition, during which AMH levels naturally rise. There was no control population, while the interpretation of AMH as a biomarker during childhood is complex. The state of cHL disease may affect AMH levels at diagnosis, potentially complicating assessment of AMH recovery as a comparison with baseline AMH. The current analysis included data up to 2-5 years post-diagnosis. WIDER IMPLICATIONS OF THE FINDINGS: The current PANCARE guideline advises to use the cyclophosphamide-equivalent dose score (CED-score, as an estimation of cumulative alkylating agent exposure) with a cut-off of 6000 mg/m2 to identify females aged <25 years at high risk of infertility. All treatment-arms of the EuroNet-PHL-C2 protocol remain below this cut-off, and based on this guideline, girls treated for cHL should therefore be considered low-risk of infertility. However, although we observed an increase in AMH after chemotherapy, it should be noted that not all girls recovered to pre-treatment AMH levels, particularly those treated for advanced stages of cHL. It remains unclear how our measurements relate to age-specific expected AMH levels and patterns. Additional (long-term) data are needed to explore clinical reproductive outcomes of survivors treated according to the EuroNet-PHL-C2 protocol. STUDY FUNDING/COMPETING INTEREST(S): The fertility add-on study was funded by the Dutch charity foundation KiKa (project 257) that funds research on all forms of childhood cancer. C.M-K., D.K., W.H.W., D.H., M.C., A.U., and A.B. were involved in the development of the EuroNet-PHL-C2 regimen. The other authors indicated no potential conflicts of interest. TRIAL REGISTRATION NUMBER: N/A.

Off-label drug use in paediatric haemato-oncology patients: financial implications and proposed solutions for Belgian patients.

Treatment of children with cancer requires access to and reimbursement of effective drugs. Children with haemato-oncological diseases are often treated according to established treatment recommendations or in the framework of late-phase clinical trials. These often involve the use of drugs authorised for adults but which, however, have been used for many years in paediatrics with no perspective of authorisation in children. In Belgium, medicines are predominantly reimbursed based on their authorised indication. As a consequence, many drugs used in paediatric haemato-oncology are used off-label, despite their status of 'standard of care'. As reimbursement is often not available, alternative ways for funding need to be explored, which causes a significant administrative burden for healthcare providers and emotional distress for the parents. Solutions to organise a systematic reimbursement of standard of care off-label used drugs are described.Conclusion: A number of structural solutions are proposed, and we hope that they might guide health authorities to provide a solution to the problem caused by the lack of reimbursement of some standard of care medicines for children with cancer. What is Known: • Off-label drug use is frequently observed in paediatric haemato-oncology and compromises-in some countries-reimbursement. What is New: • An estimation of the impact of non-reimbursed drugs in Belgium is provided. • Some solutions are presented to overcome this problem in Belgium.

CNS-3 status remains an independent adverse prognosis factor in children with acute lymphoblastic leukemia (ALL) treated without cranial irradiation: Results of EORTC Children Leukemia Group study 58951.

AIM: To evaluate the prognostic significance of initial central nervous system (CNS) involvement of children with acute lymphoblastic leukemia (ALL) enrolled in the EORTC 58951 trial. PATIENTS AND METHODS: From 1998 to 2008, 1930 ALL patients were included in the randomized EORTC 58951 trial. Overall treatment intensity was adjusted according to known prognostic factors including the level of minimal residual disease after induction treatment. CNS-directed therapy comprised four to 11 courses of i.v. methotrexate (5g/m2), and 10 to 19 intrathecal chemotherapy injections, depending on risk group and CNS status. Cranial irradiation was omitted for all patients. RESULTS: The overall 8-year event-free survival (EFS) and overall survival (OS) rates were 81.3% and 88.1%, respectively. In the CNS-1, TPL+, CNS-2, and CNS-3 groups, the 8-year EFS rates were 82.1%, 77.1%, 78.3%, and 57.4%, respectively. Multivariable analysis indicated that initial CNS-3 status, but not CNS-2 or TLP+, was an independent adverse predictor of outcome. The 8-year incidence of isolated CNS relapse was 1.7% and of isolated or combined CNS relapse it was 3.7%. NCI high-risk group, male sex, CNS-2 and CNS-3 status were independent predictors for a higher incidence of any CNS relapse. CONCLUSIONS: CNS-3 status remains associated with poor prognosis and requires intensification of both systemic and CNS-directed therapy. This trial was registered at https://clinicaltrials.gov/under/NCT00003728.

Non-anaplastic peripheral T cell lymphoma in children and adolescents-an international review of 143 cases.

Peripheral T cell lymphomas (PTCL) are rare in children and adolescents, and data about outcome and treatment results are scarce. The present study is a joint, international, retrospective analysis of 143 reported cases of non-anaplastic PTCL in patients <19 years of age, with a focus on treatment and outcome features. One hundred forty-three patients, between 0.3 and 18.7 years old, diagnosed between 2000 and 2015 were included in the study. PTCL not otherwise specified was the largest subgroup, followed by extranodal NK/T cell lymphoma, hepatosplenic T cell lymphoma (HS TCL), and subcutaneous panniculitis-like T cell lymphoma (SP TCL). Probability of overall survival (pOS) at 5 years for the whole group was 0.56 ± 0.05, and probability of event-free survival was (pEFS) 0.45 ± 0.05. Patients with SP TCL had a good outcome with 5-year pOS of 0.78 ± 0.1 while patients with HS TCL were reported with 5-year pOS of only 0.13 ± 0.12. Twenty-five percent of the patients were reported to have a pre-existing condition, and this group had a dismal outcome with 5-year pOS of 0.29 ± 0.09. The distribution of non-anaplastic PTCL subtypes in pediatric and adolescent patients differs from what is reported in adult patients. Overall outcome depends on the subtype with some doing better than others. Pre-existing conditions are frequent and associated with poor outcomes. There is a clear need for subtype-based treatment recommendations for children and adolescents with PTCL.

Ovarian cancer in children and adolescents: A rare disease that needs more attention.

Ovarian cancer is rare in childhood. This explains why there are only scattered reports on it in the literature and why there is a lack of specific pediatric treatment. This paper gives an overview of the Belgian data from 2004 to 2013 and reviews the literature. To index ovarian masses and malignancies in children better in the future, worldwide data collection should be improved and reproducible definitions of 'childhood', 'malignancy' and 'ovarian mass' need to be adopted.

IKZF1 deletion is an independent prognostic marker in childhood B-cell precursor acute lymphoblastic leukemia, and distinguishes patients benefiting from pulses during maintenance therapy: results of the EORTC Children's Leukemia Group study 58951.

The added value of IKZF1 gene deletion (IKZF1(del)) as a stratifying criterion in B-cell precursor acute lymphoblastic leukemia (BCP-ALL) is still debated. We performed a comprehensive analysis of the impact of IKZF1(del) in a large cohort of children (n=1223) with BCR-ABL1-negative BCP-ALL treated in the EORTC-CLG trial 58951. Patients with IKZF1(del) had a lower 8-year event-free survival (EFS, 67.7% versus 86.5%; hazard ratio (HR)=2.41; 95% confidence interval (CI)=1.75-3.32; P<0.001). Importantly, despite association with high-risk features such as high minimal residual disease, IKZF1(del) remained significantly predictive in multivariate analyses. Analysis by genetic subtype showed that IKZF1(del) increased risk only in the high hyperdiploid ALLs (HR=2.57; 95% CI=1.19-5.55; P=0.013) and in 'B-other' ALLs, that is, lacking classifying genetic lesions (HR=2.22; 95% CI=1.45-3.39; P<0.001), the latter having then a dramatically low 8-year EFS (56.4; 95% CI=44.6-66.7). Among IKZF1(del)-positive patients randomized for vincristine-steroid pulses during maintenance, those receiving pulses had a significantly higher 8-year EFS (93.3; 95% CI=61.3-99.0 versus 42.1; 95% CI=20.4-62.5). Thus, IKZF1(del) retains independent prognostic significance in the context of current risk-adapted protocols, and is associated with a dismal outcome in 'B-other' ALL. Addition of vincristine-steroid pulses during maintenance may specifically benefit to IKZF1(del) patients in preventing relapses.

[Retroperitoneal mass in children : clinical cases of Wilms tumor and neuroblastoma]. / Le cas clinique du mois. Les masses rétropéritonéales chez l'enfant : a propos d'une tumeur de Wilms et d'un neuroblastome.

Detection of a retroperitoneal mass in children needs a fast and accurate exploration. We present the case-reports of 2 children under the age of 5 years admitted to the University Hospital of Liège, one with a Wilms tumor and one with a neuroblastoma.

[Exploring . . . a retroperitoneal mass in children]. / Comment j'explore ... une masse retroperitoneale chez l'enfant.

Detection of a retroperitoneal mass in children needs a fast and accurate exploration. Wilms tumor and neuroblastoma, the most frequent, will be presented more in detail including their clinical and biological characteristics, their diagnostic tests and their primary therapeutic treatments.

Results of 58872 and 58921 trials in acute myeloblastic leukemia and relative value of chemotherapy vs allogeneic bone marrow transplantation in first complete remission: the EORTC Children Leukemia Group report.

The first EORTC (European Organization of Research and Treatment of Cancer) acute myeloblastic leukemia (AML) pilot study (58872) was conducted between January 1988 and December 1991. Out of 108 patients, 78% achieved complete remission (CR), and event-free survival (EFS) and survival rates (s.e., %) at 7 years were 40 (5) and 51% (6%), respectively. It indicated that mitoxantrone could be substituted for conventional anthracyclines in the treatment of childhood AML without inducing cardiotoxicity. The aim of the next EORTC 58921 trial was to compare the efficacy and toxicity of idarubicin vs mitoxantrone in initial chemotherapy courses, further therapy consisting of allogeneic bone marrow transplantation (alloBMT) in patients with an HLA-compatible sibling donor or chemotherapy in patients without a donor. Out of 177 patients, recruited between October 1992 and December 2002, 81% reached CR. Overall 7-year EFS and survival rates were 49 (4) and 62% (4%), respectively. Out of 145 patients who received the first intensification, 39 had a sibling donor. In patients with or without a donor, the 7-year disease-free survival (DFS) rate was 63 (8) and 57% (5%) and the 7-year survival rate was 78 (7) and 65% (5%), respectively. Patients with favorable, intermediate and unfavorable cytogenetic features had a 5-year EFS rate of 57, 45 and 45% and a 5-year survival rate of 89, 67 and 53%, respectively.

Medullary thyroid carcinoma in a child with a new RET mutation and a RET polymorphism.

We report a 12 year old boy with an isolated medullary thyroid carcinoma (MTC). A mutation analysis of the RET-proto-oncogene in this boy showed an in frame insertion-deletion mutation (insTTCTdelG) at codon 666 of the RET proto-oncogene. This RET mutation has not been reported previously. The boy's mother and his 82-year-old maternal grandfather showed the same mutation. None of the two ever showed symptoms of MTC. The mother underwent a preventive total thyroidectomy and pathological examination showed C-cell hyperplasia and early MTC. Further genetic analysis showed that the boy inherited a well-known coding polymorphism in exon 11 (G691S) from his father. Therefore the boy is a compound heterozygote for the insertion-deletion mutation at codon 666 and the G691S polymorphism in the RET gene. We hypothesize that the insTTCTdelG mutation at codon 666 is associated with low penetrance for MTC and that the young age of MTC in the reported child results most likely from the additive effects of both mutations (insTTCTdelG and G691S).

Value of intravenous 6-mercaptopurine during continuation treatment in childhood acute lymphoblastic leukemia and non-Hodgkin's lymphoma: final results of a randomized phase III trial (58881) of the EORTC CLG.

Between November 1990 and November 1996, EORTC Children Leukemia Group conducted a randomized trial in de novo acute lymphoblastic leukemia and lymphoblastic non-Hodgkin's lymphoma patients using a Berlin-Frankfurt-Munster protocol to evaluate the monthly addition of intravenous 6-mercaptopurine (i.v. 6-MP) (1 g/m(2)) to conventional continuation therapy comprising per oral MTX weekly and 6-MP daily. Only during the first 18 months of the randomization period, 6-MP p.o. was interrupted for 1 week after each i.v. 6-MP. A total of 877 patients was randomized to either no i.v. 6-MP (Arm A) or additional i.v. 6-MP (Arm B). A total of 217 relapses (91 in Group A vs 128 in Group B) and 13 deaths in CR (5 vs 8) were reported; a total of 134 patients (55 vs 79) died. The median follow-up was 7.6 years. At 8 years, the disease-free survival rate was lower (P=0.005) in Arm B (69.1% (s.e.=2.2%)) than in Arm A (77.9% (s.e.=2.0%)), and the hazard ratio was 1.45 (95% CI 1.12-1.89). In conclusion, as delivered in this study, i.v. 6-MP was detrimental to event-free survival.

A new recurrent inversion, inv(7)(p15q34), leads to transcriptional activation of HOXA10 and HOXA11 in a subset of T-cell acute lymphoblastic leukemias.

Chromosomal translocations with breakpoints in T-cell receptor (TCR) genes are recurrent in T-cell malignancies. These translocations involve the TCRalphadelta gene (14q11), the TCRbeta gene (7q34) and to a lesser extent the TCRgamma gene at chromosomal band 7p14 and juxtapose T-cell oncogenes next to TCR regulatory sequences leading to deregulated expression of those oncogenes. Here, we describe a new recurrent chromosomal inversion of chromosome 7, inv(7)(p15q34), in a subset of patients with T-cell acute lymphoblastic leukemia characterized by CD2 negative and CD4 positive, CD8 negative blasts. This rearrangement juxtaposes the distal part of the HOXA gene cluster on 7p15 to the TCRbeta locus on 7q34. Real time quantitative PCR analysis for all HOXA genes revealed high levels of HOXA10 and HOXA11 expression in all inv(7) positive cases. This is the first report of a recurrent chromosome rearrangement targeting the HOXA gene cluster in T-cell malignancies resulting in deregulated HOXA gene expression (particularly HOXA10 and HOXA11) and is in keeping with a previous report suggesting HOXA deregulation in MLL-rearranged T- and B cell lymphoblastic leukemia as the key factor in leukaemic transformation. Finally, our observation also supports the previous suggested role of HOXA10 and HOXA11 in normal thymocyte development.

Fusion of NUP214 to ABL1 on amplified episomes in T-cell acute lymphoblastic leukemia.

In T-cell acute lymphoblastic leukemia (T-ALL), transcription factors are known to be deregulated by chromosomal translocations, but mutations in protein tyrosine kinases have only rarely been identified. Here we describe the extrachromosomal (episomal) amplification of ABL1 in 5 of 90 (5.6%) individuals with T-ALL, an aberration that is not detectable by conventional cytogenetics. Molecular analyses delineated the amplicon as a 500-kb region from chromosome band 9q34, containing the oncogenes ABL1 and NUP214 (refs. 5,6). We identified a previously undescribed mechanism for activation of tyrosine kinases in cancer: the formation of episomes resulting in a fusion between NUP214 and ABL1. We detected the NUP214-ABL1 transcript in five individuals with the ABL1 amplification, in 5 of 85 (5.8%) additional individuals with T-ALL and in 3 of 22 T-ALL cell lines. The constitutively phosphorylated tyrosine kinase NUP214-ABL1 is sensitive to the tyrosine kinase inhibitor imatinib. The recurrent cryptic NUP214-ABL1 rearrangement is associated with increased HOX expression and deletion of CDKN2A, consistent with a multistep pathogenesis of T-ALL. NUP214-ABL1 expression defines a new subgroup of individuals with T-ALL who could benefit from treatment with imatinib.