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Inherited differences in thiopurine methyltransferase (TPMT) activity are an important factor in the wide interindividual variations observed in the clinical response to thiopurine chemotherapy. The aim of this study was to establish a population range for red blood cell (RBC) TPMT activity in children with acute lymphoblastic leukaemia (ALL) at disease diagnosis. An additional aim was to investigate factors that can influence TPMT activity within the RBC.Blood samples were collected from children with ALL at disease diagnosis, prior to any blood transfusions, as part of the nationwide UK MRC ALL97 therapeutic trial. RBC TPMT activity was measured by h.p.l.c. RBCs were age-fractionated on Percoll density gradients.Pretreatment blood samples were received from 570 children within 3 days of venepuncture. TPMT activities at disease diagnosis ranged from 1.6 to 23.6 units/ml RBCs (median 7.9) compared with 0.654-18.8 units (median 12.9), in 111 healthy control children (median difference 4.5 units, 95% CI 3.9, 5.1 units, P0.001). A TPMT quality control sample, aliquots of which were assayed in 60 analytical runs over a 12 month period, contained a median of 11.98 units with a CV of 11.6%. Seven children had their RBCs age-fractionated on density gradients. TPMT activities in the top gradient (young cells) ranged from 4.2 to 14.1 units (median 7.5) and in the bottom gradient (old cells) 1.5-12.6 units (median 4.7 units), median difference 2.3 units, 95% CI 0.7, 4.1, P = 0.035.Circulating RBCs do not constitute a homogeneous population. They have a life span of around 120 days and during that time undergo a progressive ageing process. The anaemia of ALL is due to deficient RBC production. The results of this study indicate that RBC TPMT activities are significantly lower in children with ALL at disease diagnosis. This may be due, at least in part, to a relative excess of older RBCs.

Results of three consecutive completed UK trials (1980-1997) for childhood lymphoblastic leukaemia are presented. National accrual has progressively increased so that over 90% of all the country's ALL cases were treated on the latest trial reported, UKALLXI. From 1980 to 1990, event-free and overall survival progressively improved, following adoption of an American therapy template and use of two post-remission intensification modules. Since 1990 despite demonstration of the benefit of a third intensification module overall event-free survival (EFS) has not improved further. Survival remains high due to a good retrieval rate especially for those relapsing off treatment after receipt of two intensification pulses. Possible reasons for the plateau in event-free survival (including type and dose of induction steroid, dropping of induction anthracycline, type and dose of asparaginase, gaps early in therapy following intensification, and overall lack of compliance in maintenance) are being explored in the latest protocol ALL '97. Cranial irradiation had been successfully replaced by a long course of intrathecal methotrexate injections for the majority of patients. Age (10 years) sex (male) and white count >50 x 10(9)/l plus slow initial bone marrow clearance were consistently the most important independent prognostic indicators during this time period. Rome/NCI criteria accurately predict standard and high-risk groups for B cell lineage, but not consistently for T cell disease. This international collaborative venture might help us to define those truly at highest risk, and how we can optimise therapy for specific subgroups including T-ALL and those with unfavourable cytogenetics.

Acute lymphoblastic leukaemia (ALL) is rare under 1 year and has a poor prognosis. Only 14 of 48 infants treated on two consecutive MRC UKALL trials remain alive in first remission. Forty infants have subsequently been treated on a protocol incorporating further intensification with an option for high-dose chemotherapy and autologous or allogeneic bone marrow transplantation. The results show no improvement over previous trials largely due to the number of remission deaths; four of nine being associated with toxicity of 5 days of etoposide and cytarabine. Only three of 11 children treated by high-dose chemotherapy and transplantation remain alive in remission. Multivariate analysis of the factors influencing prognosis in all 88 infants showed that only age was significant. Event-free survival was 40% at 5 years for children over 26 weeks but under 10% for younger children. These results show the susceptibility of infants to the toxicity of intensive chemotherapy and do not support the use of short term high-dose chemotherapy alone in the management of infant leukaemia. Despite the unique biological features of infant ALL it appears that these patients also may benefit from longer courses of treatment with a maintenance (continuing) phase.

Blast cell morphology of children with lymphoblastic leukaemia (ALL) entering two national multicentre trials was prospectively reviewed by three haematologists to define the clinical importance of (a) French-American-British (FAB) classification, (b) the presence of cytoplasmic vacuoles, and (c) the presence of 'hand-mirror' cells. Of 2135 evaluable children, 1907 (89%) had FAB L1 morphology and 228 (11%) L2. (L3 patients were not eligible for the trials in question). L2 patients more frequently had residual disease 14 d after starting treatment and had a significantly inferior disease-free survival, but not if the analysis was stratified for age, sex and diagnostic white cell count (WBC). 627 (29%) had blast cells with cytoplasmic vacuoles, and showed a significant survival advantage over the remainder. Vacuoles were positively associated with a low WBC, age range 1-6 years and blast cell positivity for CD10, but their benign influence was apparent even when these variables were taken into account. 'Hand-mirror' (HM) cells were only studied in UKALL X, and were noted in 316/1402 (23%) children. There appeared to be an inverse correlation between HM cells and cytoplasmic vacuoles and a weak association with T-cell immunophenotype, but no prognostic significance was evident. FAB classification appears to be of less prognostic importance than has previously been supposed, though L2 disease is more resistant to current remission induction regimens. Hand-mirror cells may be more common in T-ALL, but are seen in all types and are not related to prognosis. Cytoplasmic vacuoles are predictive of a good response to current therapeutic schedules even allowing for other prognostic variables, and are the single most important morphological feature relating to prognosis in childhood ALL.

The effect of randomly allocated testicular irradiation on the subsequent incidence of testicular infiltration and disease-free survival was assessed in two Medical Research Council Childhood Leukemia Trials. UKALL VI and UKALL VII. None of the 83 boys who actually received testicular radiotherapy subsequently developed gonadal disease. whereas 18 of the 163 who were not irradiated did. Despite this there is no apparent difference in disease-free survival for those randomized to receive testicular irradiation compared to those who were not, after a minimum of 8 years follow up. Although prophylactic testicular irradiation appears to prevent subsequent gonadal relapse there is no evidence that it improves overall prognosis when adequate systemic chemotherapy is used. As it has considerable long-term side effects it cannot be recommended as routine therapy.