Randomised Introduction of 2-CDA as Intensification during Consolidation for Children with High-risk AML--results from Study AML-BFM 2004.

BACKGROUND: The outcome in children and adolescents with high-risk (HR) acute myeloid leukemia (AML) is still unsatisfactory. Therefore, in study AML-BFM 2004 we aimed to improve outcome of HR-patients by adding moderately dosed 2-Chloro-2-Deoxyadenosine (2-CDA) to the respective consolidation treatment backbone without increasing toxicity. The aim was to improve prognosis especially in FAB M4/M5/MLL patients, who represent the largest subgroup of HR patients. PATIENTS AND METHODS: In total, 343 children and adolescents with HR-AML were randomized to receive or not 2-CDA (6 mg/m²/d, days 1, 3) in combination with cytarabine/idarubicine (AI=500 mg/m² cytarabine 5 days continuous infusion plus 7 mg/m²/d idarubicin, days 3 and 5). RESULTS: RESULTS for patients of the AI/2-CDA arm (n=168) vs. the AI-arm (n=175) were similar: 5-year overall survival 68±4 vs. 72±4%, plogrank=0.38, event-free survival 53±4 vs. 49±4%, plogrank=0.77; cumulative incidence of relapse at 5 years: 35±4 vs. 37±4%, p(Gray)=0.89. RESULTS in patients with MLL rearrangement or FAB M4/M5 were also similar in the treatment groups. In addition, toxicities did not differ between the two arms. CONCLUSION: We conclude that additional, moderate dose 2-CDA does not improve prognosis in HR-patients when given during consolidation treatment. Its effect might be too low in this multidrug regimen, where the strongest effects are achieved during induction, or the chosen dose of 2-CDA might have been too low.

Re-induction with L-DNR/FLAG improves response after AML relapse, but not long-term survival.

BACKGROUND: According to the results of the international study Relapsed AML 2001/01 response was better after re-induction with L-DNR/FLAG (liposomal daunorubicin, fludarabine, cytarabine, G-CSF) compared to FLAG only but survival rate was not improved. However, the findings might be group-specific. METHOD: Patient characteristics, actual therapy given and long-term course of the disease in 155 pediatric patients (including non-randomized) with first relapse and 10 primary nonresponders treated in Germany were analyzed. RESULTS: Overall 4-year survival rates after relapse were similar in the 2 treatment groups L-DNR/FLAG and FLAG (0.43 ± 0.05 vs. 0.47 ± 0.06, p(log-rank)=0.47). The rate of randomization was low (65%) and 5% of the 101 randomized patients changed the treatment arm. Therefore, induction was based in 40% patients on an individual decision with preference for L-DNR/FLAG. There were less patients with favorable cytogenetics and morphology in the L-DNR/FLAG-group (p<0.04). Response to the first re-induction course at day 28 tended to be more unfavorable with FLAG only. In this patient group protocol intensifications were more frequent as compared to the L-DNR/FLAG-group (p=0.07), and late CR could be achieved after intensification in 9/18 poor responding patients. CONCLUSION: The initial selection bias of relapse patients with unfavorable risk factors to the disadvantage of the L-DNR/FLAG-group and the more drug- and time-intensive treatment after 1(st) re-induction given in the FLAG-group may have nullified the initial beneficial effect of L-DNR containing re-induction therapy and led to similar and relatively favorable survival rates in both treatment groups in Germany.

Musculoskeletal pain: a new algorithm for differential diagnosis of a cardinal symptom in pediatrics.

Musculoskeletal pain (MSP) is a common childhood complaint associated with multiple differential diagnoses, including cancer. Considering the expanding spectrum of diagnostics, evaluat-ing a young patient with MSP is a challenge today, particularly for non-specialists in a primary care setting. Since childhood cancer is rare and most cardinal symptoms mimic rather non-serious diseases, misdiagnosis is not uncommon, but of significant prognostic relevance. To build the appropriate bridge between primary and secon-dary care for a child presenting with MSP, thereby preventing treatment delay and longterm sequelae, initial evaluation should follow a comprehensive, multidisciplinary, systematic and stepwise approach, which unites the patient's individual anamnestic, psychosocial, and clinical charac-teristics. After a systematic review of the literature, we generated multidisciplinarily quality-assured recommendations for efficient, rational and cost-effective primary care assessment of pediatric MSP. The algorithm promotes the identification and structured interpretation of the patient's individual clinical clues. It should serve the primary care physician to recognize when further intervention, rather than reassurance and follow-up, is needed using the minimum amount of testing to make an appropriate, prompt diagnosis in the clinical situation "child presenting with MSP". A German version of this algorithm has been published in the Guideline-Portal of The Association of the Scientific Medical Societies ("Arbeitsgemeinschaft der Wissenschaftlichen Medizinischen Fachgesellschaften", AWMF) in November 2013.

Effective childhood cancer treatment: the impact of large scale clinical trials in Germany and Austria.

In Germany and Austria, more than 90% of pediatric cancer patients are enrolled into nationwide disease-specific first-line clinical trials or interim registries. Essential components are a pediatric cancer registry and centralized reference laboratories, imaging review, and tumor board assistance. The five-year overall survival rate in countries where such infrastructures are established has improved from <20% before 1950 to >80% since 1995. Today, treatment intensity is tailored to the individual patient's risk to provide the highest chances of survival while minimizing deleterious late effects. Multicenter clinical trials are internationalized and serve as platforms for further improvements by novel drugs and biologicals.

Development of a curative treatment within the AML-BFM studies.

The first multicenter treatment study for AML in childhood in Germany was performed from 1978 onwards. The therapy plan was designed similar to that for the acute lymphoblastic leukaemia (ALL). The drugs with the highest efficacy in AML, cytarabine cutting catara-bine and anthracyclines, were combined during induction and consolidation, followed by preventive cranial irradiation and maintenance therapy similar to that in ALL. The remission rate of the initial study was 80%, and the 5-year survival rate increased from less than 10% before 1970 to 40%. 5 subsequent trials have further increased the 5-year survival to now 70% and even 90% in the subgroup of core-binding factor leukaemias by using an intensified and optimised treatment schedule.The AML-BFM studies were the only prospective study sequence testing the benefit of cranial irradiation. Results from study -87 including the non-randomized patients showed an increased risk of CNS and/or bone marrow relapses in non-irradiated patients. Later on there was evidence that 12 Gy resulted in the same relapse rate as 18 Gy. The AML-BFM studies always used the experience from the previous study to optimize the next study. This approach was essential together with improved supportive treatment and experience of the medical staff for the step-wise and considerable increase of longterm survival within the 6 subsequent AML-BFM studies.

[Genetic prognostic factors in childhood acute myeloid leukemia]. / Prognostische Relevanz genetischer Aberrationen der akuten myeloischen Leukämie bei Kindern und Jugendlichen.

The survival rate of children and adolescents suffering acute myeloid leukemia (AML) has been significantly improved within the last decades. This has been achieved by a continuously intensified therapy and progress in supportive care to prevent and treat complications. In Germany, the AML-BFM trials 98 (n=413) and 2004 (n=499) enrolled 912 children and adolescents as protocol patients (1998-2010). The 5-year-overall survival was 71±2%. In the previous studies prognosis and subsequent treatment stratification based on morphology, cytochemistry and white blood cell count. Today, the identification of new genetic aberrations in AML enables a genetically determined estimation of prognosis, although treatment response must be considered for treatment stratification. The group with a favorable prognosis summarized AML with t(8;21), inv(16), t(15;17), t(1;11), and AML with normal karyotype and NPM1-mutation (n=253; EFS 74±3%, OS 88±2%). A poor prognosis (HR-group) must be expected in AML with t(4;11), t(5;11), t(6;11), t(6;9), t(7;12), t(9;22), Monosomy 7, combined FLT3/WT1-mutation, and AML with der(12p)-aberration (n=101; EFS 30±5%; OS 56±5%). The intermediate group summarizes all other subgroups especially AML with normal karyotyp, AML with FLT3-ITD or t(9;11) (n=558; EFS 43±2%; OS 64±2%). The validation of the internationally identified, genetically determined prognostic factors within the AML-BFM (Germany) study population will support treatment recommendations.

[GATA1-mutation associated leukemia in children with trisomy 21 mosaic]. / GATA1-Mutations-assoziierte Leukämien bei Kindern mit Trisomie 21-Mosaik.

Mutations of the hematopoietic transcription factor GATA1 (GATA1s) are pathognomonic in newborn with transient leukemia and children with Down syndrome and myeloid leukemia (ML-DS). Both TL and ML-DS can also occur in children with trisomy 21 mosaic.Between 2002 and 2011, 15 newborns and infants were diagnosed with DS mosaic. 9 of them presented with TL and 8 children suffered from ML-DS; 2 of them with a history of TL. In children without stigmata the special morphology and immunophenotype of blasts triggered the screening for GATA1 mutation and trisomy 21 mosaic.All newborns with TL achieved complete remission (CR). Due to clinical symptoms caused by the leukemic blasts, in 3 children low-dose cytarabine was applied. 1 patient died due to cardiac defect. In all patients GATA 1 s was confirmed. 6 children with ML-DS were initially treated according the AML-BFM protocol. After ML-DS was confirmed, therapy was continued with the intensity reduced schedule according to the ML-DS 2006 protocol. All children are still in CR (follow-up 1.8-7 years, median 2.7 yrs). 2 children with unknown trisomy 21 mosaic were diagnosed as acute megakaryoblastic leukemia (AMKL) and treated according the high risk arm of the AML-BFM 2004 including allogeneic stem cell transplantation in one child). GATA1 mutation was identified retrospectively. Both children are alive in CR.GATA1s associated leukemia has to be excluded in all young children with AMKL (<5 years old) to prevent overtreatment. Treatment with reduced intensity seems sufficient in children trisomy 21 mosaic and ML-DS.

Stability and prognostic influence of FLT3 mutations in paired initial and relapsed AML samples.

In acute myeloid leukemia (AML), activating mutations in the fms-like tyrosine kinase 3 (FLT3) gene predict poor prognosis. We determined FLT3 internal tandem duplications (FLT3/ITD) and D835 point mutations in paired initial and relapse samples from 80 pediatric and adult AML patients. One D835 point mutation was found in an initial pediatric AML sample. Fms-like tyrosine kinase 3/ITDs were present in 21 initial and 22 relapse samples (26.3 and 27.5%, respectively). Interestingly, FLT3/ITD positivity was related to a significantly shorter time to relapse, most pronounced when the ITD-positive status was found at relapse (P<0.001). However, FLT3/ITD status changed between diagnosis and relapse in 14 cases. In four patients, the FLT3/ITD became undetectable at relapse in five patients FLT3/ITDs were only detected at relapse, and in five patients the length or number of FLT3/ITDs changed. Gain of FLT3/ITDs may suggest oligoclonality with selective outgrowth of the FLT3/ITD-positive clone, whereas losses may reflect ITDs in the more mature leukemic cells rather than in the leukemic stem cell, or, alternatively, that other genetic aberrations provided a greater selective advantage. Studying FLT3/ITD kinetics in minimal residual disease setting may provide some answers for the changes we observed. Fms-like tyrosine kinase 3/ITD is a relevant marker for prognosis, and remains an important target for therapeutic inhibition.

Genotype-outcome correlations in pediatric AML: the impact of a monosomal karyotype in trial AML-BFM 2004.

We conducted a cytogenetic analysis of 642 children with de novo acute myeloid leukemia (AML) treated on the AML-Berlin-Frankfurt-Münster (BFM) 04 protocol to determine the prognostic value of specific chromosomal aberrations including monosomal (MK+), complex (CK+) and hypodiploid (HK+) karyotypes, individually and in combination. Multivariate regression analysis identified in particular MK+ (n=22) as a new independent risk factor for poor event-free survival (EFS 23±9% vs 53±2% for all other patients, P=0.0003), even after exclusion of four patients with monosomy 7 (EFS 28±11%, P=0.0081). CK+ patients without MK had a better prognosis (n=47, EFS 47±8%, P=0.46) than those with MK+ (n=12, EFS 25±13%, P=0.024). HK+ (n=37, EFS 44±8% for total cohort, P=0.3) influenced outcome only when t(8;21) patients were excluded (remaining n=16, EFS 9±8%, P<0.0001). An extremely poor outcome was observed for MK+/HK+ patients (n=10, EFS 10±10%, P<0.0001). Finally, isolated trisomy 8 was also associated with low EFS (n=16, EFS 25±11%, P=0.0091). In conclusion, monosomal karyotype is a strong and independent predictor for high-risk pediatric AML. In addition, isolated trisomy 8 and hypodiploidy without t(8;21) coincide with dismal outcome. These results have important implications for risk stratification and should be further validated in independent pediatric cohorts.

AML patients with Down syndrome have a high cure rate with AML-BFM therapy with reduced dose intensity.

Despite improved prognosis in acute myelogenous leukaemia (AML) children with Down syndrome (DS), therapy-related toxicity remained a problem. We compared 67 DS patients from study AML-BFM 98 with 51 DS patients of the previous study AML-BFM 93, and the non-DS groups of both studies. Compared to non-DS patients, DS patients were treated with reduced anthracycline doses, without high-dose cytarabine/mitoxantrone and without cranial irradiation. AML-DS patients were in median 1.8 years old, and 102/118 (86%) showed the typical morphology of acute megakaryoblastic leukaemia. In study 93, seven DS patients did not receive AML-specific chemotherapy, and treatment modifications were more common. Results improved significantly for patients treated in study 98 with a 3-year survival of 91+/-4 vs 70+/-7% in study 93 (P=0.001). There were no differences in outcome concerning the age groups 0-

Treatment strategies and long-term results in paediatric patients treated in four consecutive AML-BFM trials.

A total of 1111 children with acute myeloblastic leukaemia (AML) were treated in four consecutive Berlin-Frankfurt-Münster (BFM) studies from 1978 to 1998. The first cooperative trial AML-BFM 78 established intensive chemotherapy with seven drugs, CNS irradiation and 2-year maintenance, achieving a long-term survival (overall survival (OS)) of 40%. Induction intensification in AML-BFM 83 resulted in significant improvement of disease-free survival (DFS). The risk of haemorrhage, especially in children with hyperleukocytosis, proved the high relevance of supportive care. In AML-BFM 87, the benefit of CNS irradiation in preventing CNS/systemic relapses was demonstrated. In AML-BFM 93, the introduction of idarubicin during first induction followed by intensification with HAM increased the 5-year EFS, DFS and OS to 50+/-2, 61+/-3 and 57+/-2%, respectively. Stem cell transplantation (SCT), as applied in high-risk patients with a matched related donor, did not significantly improve the outcome compared to chemotherapy alone. In spite of treatment intensification, the therapy-related death rate decreased from trial to trial, mainly during induction. The future aim is to reduce long-term sequelae, especially cardiotoxicity, by administration of less cardiotoxic drugs, and toxicity of SCT by risk-adapted indications. The AML-BFM studies performed in three European countries with >70 cooperating centres have significantly improved the outcome in AML children; nevertheless, increasing experience with these intensive treatment regimens is of fundamental importance to reduce fatal complications.

Common genetic variants in the interleukin-6 and chitotriosidase genes are associated with the risk for serious infection in children undergoing therapy for acute myeloid leukemia.

Infectious complications represent a substantial cause of morbidity and mortality in children undergoing therapy for acute myeloid leukemia (AML). Since it has been shown that alterations in innate immune pathways contribute to the risk for serious infections, we analyzed well-characterized variants in innate immune genes (TNF, IL6, IL8, MPO, CHIT, FCGR2A, TLR2, and TLR4) to determine their possible contribution to infectious complications during therapy for pediatric AML. The study population consisted of 168 North European Caucasian children enrolled on the clinical trial AML-BFM 93. We found an association between Gram-negative bacterial infection and common, functional variants in two genes, IL6 and CHIT. The risk for infection was significantly higher in children with the G allele in the IL6 promoter at -174 bp (P=0.026) and in patients with the H allele of CHIT (P=0.033). The promoter variant in IL6 has been shown to increase expression while the H allele disrupts both function and circulating levels. Our data suggest that variant alleles of both IL6 and CHIT could influence susceptibility to infection with Gram-negative bacteria in children undergoing therapy for AML. Follow-up studies, namely replication association studies and in vitro investigation of these common polymorphisms, are warranted to confirm these observations.

Mutations in KIT and RAS are frequent events in pediatric core-binding factor acute myeloid leukemia.

Activating mutations in RAS and receptor tyrosine kinases such as KIT and FLT3 are hypothesized to cooperate with chimeric transcription factors in the pathogenesis of acute myeloid leukemia (AML). To test this hypothesis, we genotyped 150 pediatric AML samples for mutations in KIT (exons 8, 17), NRAS and KRAS (exons 1, 2) and FLT3/ITD. This is the largest cohort of pediatric AML patients reported thus far screened for all four mutations. Of the children with AML, 40% had a mutation in KIT (11.3%), RAS (18%) or FLT3/ITD (11.1%), and 70% of cases of core-binding factor (CBF) leukemia were associated with a mutation of KIT or RAS. Mutations in RAS or FLT3/ITD were frequently found in association with a normal karyotype. Patients with a FLT3/ITD mutation had a significantly worse clinical outcome. However, the presence of a KIT or RAS mutation did not significantly influence clinical outcome. We demonstrate that KIT exon 8 mutations result in constitutive ligand-independent kinase activation that can be inhibited by clinically relevant concentrations of imatinib. Our results demonstrate that abnormalities of signal transduction pathways are frequent in pediatric AML. Future clinical studies are needed to determine whether selective targeting of these abnormalities will improve treatment results.

Infectious complications in children with acute myeloid leukemia: decreased mortality in multicenter trial AML-BFM 2004.

Infections are an important cause for morbidity and mortality in pediatric acute myeloid leukemia (AML). We therefore characterized infectious complications in children treated according to the trial AML-BFM 2004. Patients with Down syndrome were excluded from the analysis. Data were gathered from the medical records in the hospital where the patients were treated. A total of 405 patients (203 girls; median age 8.4 years) experienced 1326 infections. Fever without identifiable source occurred in 56.1% of the patients and clinically and microbiologically documented infections in 17.5% and 32.4% of the patients, respectively. In all, 240 Gram-positive (112 viridans group streptococci) and 90 Gram-negative isolates were recovered from the bloodstream. Invasive fungal infection was diagnosed in 3% of the patients. Three children each died of Gram-negative bacteremia and invasive aspergillosis, respectively. As compared with the results of AML-BFM 93 with lower dose intensity, infection-related morbidity was slightly higher in AML-BFM 2004 (3.3. versus 2.8 infections per patient), whereas infection-related mortality significantly decreased (1.5% versus 5.4%; P=0.003). Specific anti-infective recommendations included in the treatment protocol, regular training courses for pediatric hematologists and increasing experience may be the reason for reduced infection-related mortality in children with AML. Further studies are needed to decrease infection-related morbidity.

Does cranial irradiation reduce the risk for bone marrow relapse in acute myelogenous leukemia? Unexpected results of the Childhood Acute Myelogenous Leukemia Study BFM-87.

PURPOSE: One of the goals of study AMA-BFM-87 was to test prospectively in acute myelogenous leukemia (AML) patients if cranial irradiation could be replaced by late intensification therapy with high-dose cytarabine (Ara-C) and etoposide (VP-16). PATIENTS AND METHODS: Patients with a low risk of CNS relapses (ie, no initial CNS disease, WBC count at diagnosis < or = 70.000/microL) were randomized for irradiation (group A, 31 patients). In 25 patients (group B), randomization was refused. As interim results showed no increase of CNS relapses in nonirradiated patients, prophylactic irradiation was discontinued after 2 1/2 years to prevent unnecessary CNS toxicity. Forty-four patients (group C) entered the study after randomization had been stopped. RESULTS: In all patients with a low risk of CNS recurrences (n = 100), a significantly higher probability of relapse-free interval (pRFI) of 5 years was found in irradiated patients (pRFI = .78) compared with nonirradiated patients (pRFI = .41) (P = .007). Moreover, a slightly higher incidence of CNS relapses was observed in nonirradiated patients. Due to the small number of patients, this was not observed when randomized patients only were analyzed. In accordance with these findings, the favorable outcome of low-risk patients in the preceding study, AML-BFM-83 (pRFI > .80), could only be reproduced in study AML-BFM-87 in patients who had received cranial irradiation. CONCLUSION: These results indicate that cranial irradiation should be an integral part of the treatment of all AML patients not undergoing bone marrow transplantation. Residual blasts in the CNS may escape systemic chemotherapy and lead to recurrence of the initial disease not only in the CNS, but also in the bone marrow.

Low risk of secondary leukemias after chemotherapy without mechlorethamine in childhood Hodgkin's disease. German-Austrian Pediatric Hodgkin's Disease Group.

BACKGROUND: In the last two decades, it has become evident that secondary leukemias after Hodgkin's disease (HD) are mainly caused by the treatment with alkylating agents, especially mechlorethamine. Since 1978, the German-Austrian trials for childhood HD have used combined chemoradiotherapy without mechlorethamine. PATIENTS AND METHODS: The risk of secondary hematologic malignancies (SHM) was assessed in the total cohort of 667 children treated in four consecutive German-Austrian trials between 1978 and 1990. Primary chemotherapy for stages IA/B and IIA consisted of two cycles of vincristine, procarbazine, prednisone, and doxorubicin (OPPA) or OPA (without procarbazine) and, for more advanced stages, of two cycles of OPPA or OPA plus two, four, or six cycles of COPP or COMP (C, cyclophosphamide; M, methotrexate). Radiotherapy was given in the first study to extended fields, and in later trials to involved fields only. In 591 patients, only primary therapy was given; 76 patients (11%) needed additional salvage therapy. The actuarial survival rate at 15 years is 94%. RESULTS: SHM developed in 5 of 667 patients: four acute myeloid leukemias (AMLs) and one myelodysplastic syndrome (MDS). The estimated cumulative risk for SHM at 15 years is 1.1% (95% CI, 0.0% to 2.2%). Salvage therapy was a significant risk factor for SHM (relative risk, 7.25; P = .03), whereas age, sex, stage of HD, splenectomy, and amount of alkylating agents were not. CONCLUSION: The observed risk of SHM is smaller than in other studies (adults and children) in which chemotherapy with mechlorethamine, vincristine, procarbazine, and prednisone (MOPP) was given. This difference can be attributed to the lower cumulative doses of alkylating agents, the absence of mechlorethamine in the chemotherapy, and the small number of patients who needed salvage therapy in the presented cohort. In general, differences in the incidence of SHM after HD reflect complex differences between treatment strategies.

Improved treatment results in high-risk pediatric acute myeloid leukemia patients after intensification with high-dose cytarabine and mitoxantrone: results of Study Acute Myeloid Leukemia-Berlin-Frankfurt-Münster 93.

PURPOSE: To improve outcome in high-risk patients, high-dose cytarabine and mitoxantrone (HAM) was introduced into the treatment of children with acute myelogenous leukemia (AML) in study AML-BFM 93. Patients were randomized to HAM as either the second or third therapy block, for the purpose of evaluation of efficacy and toxicity. PATIENTS AND METHODS: A total of 471 children with de novo AML were entered onto the trial; 161 were at standard risk and 310 were at high risk. After the randomized induction (daunorubicin v idarubicin), further therapy, with the exception of HAM, was identical in the two risk groups and also comparable to that in study Acute Myeloid Leukemia-Berlin-Frankfurt-Münster (AML-BFM) 87. RESULTS: Overall, 387 (82%) of 471 patients achieved complete remission, and 5-year survival, event-free survival (EFS), and disease-free survival rates were 60%, 51%, and 62%, respectively. Idarubicin induction resulted in a significantly better blast cell reduction in the bone marrow on day 15. Estimated survival and probability of EFS were superior in study AML-BFM 93 compared with study AML-BFM 87 (P =.01, log-rank test). This improvement, however, was restricted to the 310 high-risk patients (remission rate and probability of 5-year EFS in study AML-BFM 93 v study AML-BFM 87: 78% v 68%, P =.007; and 44% v 31%, P =.01, log-rank test). Probability of 5-year EFS among standard-risk patients in study AML-BFM 93 was similar to that in study AML-BFM 87 (65% v 63%, P = not significant). Whether HAM was placed as the second or third therapy block was of minor importance. However, patients who received the less intensive daunorubicin treatment during induction benefited from early HAM. CONCLUSION: Improved treatment results in children with high-risk AML in study AML-BFM 93 must be attributed mainly to the introduction of HAM.

Immunocytochemical detection of deoxycytidine kinase in haematological malignancies and solid tumours.

BACKGROUND: Deoxycytidine kinase (dCK) is responsible for the activation of several clinically important deoxynucleoside analogues used for the treatment of haematological and solid malignancies. AIM: To measure dCK expression in tumour cells from different origins. METHOD: A rabbit antihuman dCK antibody was used for the immunocytochemical detection of dCK expression in three leukaemic cell lines (HL60, U937, and CCRF-CEM) and 97 patient samples (paediatric acute myeloid leukaemia (AML) and lymphoid leukaemia (ALL), retinoblastoma, paediatric brain tumours, and adult non-small cell lung cancer (NSCLC)). RESULTS: CCRF-CEM, U937, and HL60 cells stained positively for dCK and the degree of expression correlated with dCK activity. dCK expression varied between tumour types and between individual patients within one tumour type. dCK was located predominantly in the cytoplasm. The staining intensity was scored as negative (0), low (1+), intermediate (2+), or high (3+). Expression of dCK was high in AML blasts. In contrast, brain tumour samples expressed low amounts of dCK. dCK staining ranged from low (1+) to high (3+) in ALL blasts, retinoblastoma, and NSCLC tissue samples. Staining was consistent (interobserver variability, 88%; kappa = 0.83) and specific. Western blotting detected the dCK protein appropriately at 30 kDa, without additional bands. CONCLUSIONS: Immunocytochemistry is an effective and reliable method for determining the expression of dCK in patient samples and requires little tumour material. This method enables large scale screening of dCK expression in tumour samples.