Weight status during and after childhood acute lymphoblastic leukaemia

Background: This thesis sits within the arena of weight status during and after childhood acute lymphoblastic leukaemia (ALL), with a particular focus on the prevalence of unhealthy weight status amongst (ALL), Saudi and UK populations. Each chapter in the thesis explores different aspects of unhealthy weight status in ALL which had been highlighted as gaps in the literature at a conference in Puebla, Mexico, at the end of 2006. A summary of each study is given below. Study 1: Background: This study estimated prevalence of unhealthy weight status and metabolic syndrome (MS) amongst Saudi survivors of standard risk ALL. Methods: We recruited 56 survivors, mean age 13.4 years (SD 4.1), a mean of 9.1 years (SD 4.1) post-diagnosis. The BMI for age was used to define weight status relative to national (Saudi) and international (Cole et al., International Obesity Task Force (IOTF), World Health Organisation (WHO), and Centre for Disease Control and Prevention (CDC)) reference data. We measured body composition by dual energy X-ray absorptiometry (DXA), waist circumference, blood pressure, lipid profile (HDL-C, Triglycerides), fasting glucose and insulin. Results: According to international definitions based on BMI for age, around half of the sample had unhealthy weight status. All of the approaches based on BMI for age underestimated over-fatness, present in 27/51 (53%) of the sample according to DXA. Prevalence of MS was 7.1% (3/42 of those over 9-years old) and 5.4% (3/56) by applying the International Diabetes Federation (IDF) definition and National Cholesterol Education Program Third Adult Treatment panel Guidelines (NCEP III), respectively. However, MS by the NCEP III definition was present in 19% of the overweight and obese survivors and 7.1% of the sample had at least two of the components of MS. Conclusions: Unhealthy body weight and over-fatness may be common amongst adolescent Saudi survivors of standard risk ALL, though overweight and obesity may be no more common than in the general Saudi adolescent population. Defining weight status using BMI underestimates over-fatness in this population, as in other populations. Study 2: Background: Underweight, overweight, and obesity at diagnosis may all worsen prognosis in childhood ALL, but no studies have estimated prevalence of unhealthy weight status at diagnosis in large representative samples using contemporary definitions of weight status based on BMI for age. Methods: Retrospective study which aimed to estimate prevalence of underweight, overweight, and obesity at diagnosis for patients with childhood ALL on three successive UK treatment trials: UKALL X (1985-1990, n 1033), UKALL XI (1990- 1997, n 2031), UKALL 97/97-99 (1997-2002, n 898) .The BMI for age was used to define weight status with both UK 1990 BMI for age reference data and the IOTF definitions. Results: Prevalence of underweight was 6% in the most recent trial for which data were available. Prevalence of overweight and obesity was 35% in the most recent trial when expressed using IOTF definitions; 41% when expressed relative to UK 1990 reference data. Conclusions: Even with highly conservative estimates >40% of all UK patients with ALL were underweight, overweight, or obese at diagnosis in the most recent trial for which UK data are available (UKALL 97/99, 1997-2002). Study 3: Background: This study tested the hypothesis that overweight/obesity at diagnosis of childhood ALL was related to risk of relapse. Methods and results: In a national cohort of 1033 patients from the UK there was no evidence that weight status at diagnosis was related significantly to risk of relapse: log ranks test (p value= 0.90) with overweight and obesity as the exposure (n 917); individual (p value= 0.42) and stepwise (p value= 0.96) proportional hazards models, with BMI z score as the exposure (n 1033). Conclusion: The study does not support the hypothesis that overweight/obesity at diagnosis impairs prognosis in childhood ALL in the UK. Study 4: Background: In the sample of Saudi patients recruited to study 1 we compared DXA whole body and lumbar spine bone mineral density (BMD) using manufacturers software with a body size correction which derived bone mineral content (BMC) for bone area and Apparent bone mineral density of lumbar spine (BMADLS). Methods and results: The survivors of ALL were from Saudi Arabia (n 51, mean age 13.5 years). With no corrections, 29 patients (57%) had lumbar spine BMD z score < -1.0 and 21 (41%) had whole body BMD z score < -2. After correction, by using BMC for bone area method only 6 (12%) had lumbar spine BMC z score <-1.0 and 4 (8%) had whole body BMC z score <-2. By using BMADLS method, 18 (35%) had BMC <-1.0 and 6 (11%) had BMC Z score <-2. Conclusions: Correction for body size seems essential to accurate interpretation of DXA bone health data in adolescent survivors of ALL. The three correction methods provided different conclusions, but bone health remains a concern after treatment for ALL