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© 2003 American Society for Clinical Oncology Obesity in Adult Survivors of Childhood Acute Lymphoblastic Leukemia: A Report from the Childhood Cancer Survivor Study
From the Department of Family Practice and Community Medicine, University of Texas Southwestern Medical Center at Dallas, Dallas, TX; Department of Pediatrics, University of Minnesota, Minneapolis, MN; Department of Pediatrics, Memorial Sloan-Kettering Cancer Center, New York, NY; Cancer Prevention Research Program, Fred Hutchinson Cancer Research Center, Seattle, WA; Division of Cancer Epidemiology and Genetics, National Cancer Institute, Washington, DC; Department of Radiation Physics, University of Texas, M.D. Anderson Cancer Center, Houston, TX; and Riley Childrens Hospital, Indianapolis, IN. Address reprint requests to Kevin C. Oeffinger, MD, The University of Texas Southwestern Medical Center at Dallas, Department of Family Practice and Community Medicine, 6263 Harry Hines Blvd., Dallas, TX 75390-9067; email: kevin.oeffinger{at}utsouthwestern.edu.
Purpose: To determine whether adult survivors ( 18 years of age) of childhood acute lymphoblastic leukemia (ALL) are at increased risk for obesity and to assess patient and treatment variables that influence risk.
Patients and Methods: A retrospective cohort of participants of the Childhood Cancer Survivor Study was used to compare 1,765 adult survivors of childhood ALL to 2,565 adult siblings of childhood cancer survivors. Body-mass index (BMI; kilograms per square meter), calculated from self-reported heights and weights, was used to determine the prevalence of being overweight (BMI, 2529.9) or obese (BMI
Results: The age- and race-adjusted OR for being obese in survivors treated with cranial radiation doses
Conclusion: Cranial radiotherapy
WITH THE growing recognition of potential long-term health problems related to cancer therapy for childhood cancer, it is essential that risk factors for modifiable disease be identified and addressed. Obesity has been identified as a potential late effect of therapy in survivors of acute lymphoblastic leukemia (ALL).113 Obesity in childhood, adolescence, and young adulthood is an important predictor of eventual development of adult-onset diabetes mellitus, hypertension, dyslipidemia, and ultimately, cardiovascular disease.14 Even modest weight gain from age 20 years is strongly associated with an increased risk of coronary heart disease.15 Population-based studies indicate that more than 75% of hypertension and more than half of the variance in insulin sensitivity in the general population is accounted for by obesity.16 The risk of death from all causes, cardiovascular disease, cancer, and other diseases increases throughout the ranges of being overweight or obese in both males and females.17,18 Primary and secondary prevention of obesity have been shown to reduce morbidity and mortality related to cardiovascular disease. Thus, efforts should be directed at the identification and aggressive management of populations at risk for developing obesity. In 1986, Zee et al1 retrospectively examined medical records of 414 pediatric ALL patients treated at St. Jude Childrens Research Hospital and reported an increase in excessive weight gain. Since that time, several studies have replicated the finding that ALL survivors appear to be at risk for becoming overweight or obese by completion of therapy, attainment of final height, and early young adulthood.213 The relationship of different doses of cranial radiotherapy (CRT) or of treatment with prednisone or dexamethasone with excessive weight gain among ALL survivors is unclear; results of prior studies have been inconsistent. Studies to date have generally been limited by small sample sizes, lack of comparison groups, and short duration of follow-up. The purpose of this study was to use a large, retrospective cohort of young adult survivors of childhood ALL and siblings of childhood cancer survivors to determine whether ALL survivors are at increased risk for obesity, whether this risk is associated with CRT or a chemotherapeutic agent used in the treatment of leukemia, and whether sex and age at diagnosis modify the risk.
Subject Selection and Contact The Childhood Cancer Survivor Study (CCSS) is a multi-institutional study (see Appendix) of individuals who survived for 5 or more years after treatment for cancer, leukemia, tumor, or similar illness diagnosed during childhood or adolescence. Eligibility criteria for the CCSS cohort included diagnosis of leukemia, CNS tumors, Hodgkins disease, non-Hodgkins lymphoma, kidney tumor, neuroblastoma, soft tissue sarcoma, or bone tumor; diagnosis and initial treatment at one of the 25 collaborating CCSS institutions; diagnosis date between January 1, 1970, and December 31, 1986; age less than 21 years at diagnosis; and survival 5 years from diagnosis. The CCSS protocol and contact documents were reviewed and approved by the Human Subjects Committee at each participating institution. Baseline data were collected from members of the study cohort using a 24-page questionnaire. The baseline questionnaire was designed to capture a wide range of information including demographic characteristics, education, income, employment, insurance coverage, marital status, health habits, family history, access and utilization of medical care, medication use, frequency of diagnosed medical conditions among the group, surgical procedures, recurrent cancer, subsequent new neoplasms, and offspring or pregnancy history. Respondents were asked to record their current height and weight without shoes. Additional details regarding the methodology and cohort characteristics were published previously.19
Cancer Treatment Information
ALL Survivors and Sibling Comparison Group
The demographics and cancer treatment of the 1,765 adult survivors of childhood ALL are provided in Table 1
A cohort of sibling controls was assembled by mailing questionnaires to the nearest-age living sibling of a random sample of half of the total (all cancers) CCSS cohort. A total of 2,565 adult siblings were available for comparison with the ALL survivors. Their mean age (29.0 years) was older than that of the ALL survivors. There also were more females (52.9%) and white, non-Hispanics (92.5%).
Outcome Measures
Analysis The influence of each chemotherapeutic agent used for ALL was analyzed individually and in combination. Cumulative dosages of CRT were calculated and grouped by 5-Gy intervals from 0 to 50 Gy. A polytomous logistic regression, with the three-level polytomous outcome variable, was used to estimate odds ratios (OR) with 95% confidence intervals (95% CIs) for being overweight or obese rather than being at normal weight in ALL survivors compared with the sibling comparison group.21 Age at interview (continuous) and race (categorical) were entered as adjustment variables in assessing the effect of treatment factors. The regression model was fit for each sex separately. To account for potential within-family correlation between the survivor and his or her sibling from the same family, a bootstrap method was used by resampling the family units.22 The statistical inference was based on 1,000 bootstrap iterations in each analysis. Age at cancer diagnosis was used as an effect-modifier of treatment factors. Because some survivors may have relapsed and received their first radiation treatment several years after diagnosis, age at treatment was also assessed in those who received CRT.
Descriptive statistics of BMI and unadjusted prevalence rates for overweight or obese participants for different demographic and treatment-related variables are presented in Table 2
Higher-dose CRT (20 to 24 Gy) was associated with an increased prevalence of overweight and obese survivors in comparison with siblings. A dose response was not observed with greater increments of CRT, so all categories 20 Gy were collapsed into a single group for analysis. The addition of spinal irradiation to CRT (n = 167) was not associated with a further increase in risk for participants being overweight or obese. The age- and race-adjusted OR for obesity in survivors treated with CRT 20 Gy in comparison with siblings was 2.59 for females (95% CI, 1.88 to 3.55; P < .001) and 1.86 for males (95% CI, 1.33 to 2.57; P < .001). Female survivors were also more likely to be overweight in comparison with siblings (OR, 1.97; 95% CI, 1.44 to 2.65; P < .001).
In females, the prevalence of obesity and mean BMI were influenced by age at diagnosis. For females treated with CRT
The association of age at diagnosis (or treatment) and obesity was not apparent in males. For those treated with CRT 20 Gy, the age- and race-adjusted BMI was 26.6, 26.9, 26.5, and 24.4 for 0 to 4, 5 to 9, 10 to 14, and 15 to 21 years of age at diagnosis, respectively (P = .17). The odds of being obese were significantly increased for males diagnosed in the three younger categories; however, there was not a trend for more significant changes for those age 0 to 4 at diagnosis. Similar to females, males diagnosed at 15 to 21 years of age were not more likely to be obese or overweight in comparison with the siblings. The interval from cancer diagnosis to age at interview did not modify the outcomes when adjusted for age and race.
Although there have been several studies to date about the possible relationship between ALL treatment and subsequent obesity, assessment of risk based on radiation dose, sex, and age at diagnosis has been limited by small sample sizes and lack of optimal comparison groups. This analysis of a large, retrospective cohort of 1,765 adult survivors of childhood ALL with a sibling comparison group firmly establishes that previous treatment with CRT 20 Gy is associated with an increased risk for obesity, particularly for females treated at a younger age. Obesity that develops or extends into the adolescent and young adult years is strongly associated with several common adult health problems, including adult-onset diabetes mellitus, hypertension, dyslipidemia, cardiovascular disease, endometrial cancer, and osteoarthritis and may be associated with breast and colon cancer. Recognizing the association between higher-dose CRT ( 20 Gy) and obesity is a necessary step to developing targeted surveillance and intervention studies intended to modify risk.
Previous studies113 have identified an increase in weight gain by the end of therapy and during early follow-up periods in childhood ALL survivors, both in those treated with chemotherapy only and in those also treated with CRT. Four studies of ALL survivors in the early follow-up period or by time of final height attainment did not find a difference in measures of obesity between those who had been treated with CRT
This CCSS analysis of 1,765 ALL survivors who were 18 years of age or older at time of study included 421 survivors who had received chemotherapy only, 503 survivors who had received CRT 10 to 19 Gy, and 841 survivors who had received CRT It is of interest that females exposed to cranial irradiation at a young age tend to be more vulnerable than males and are at increased risk of developing a variety of adverse outcomes in addition to obesity. Neurocognitive impairment,23,24 earlier onset of puberty,25,26 and reduced final height27 have all been found to occur at higher rates in young females treated with cranial irradiation. Although the pathogenesis of these associations remains unclear, some authors have postulated that this increased vulnerability of the female brain may be related to more rapid brain growth during early childhood in females compared with that in males.23 Recognizing this strong association of higher-dose CRT and obesity, modified by early age at treatment, it is likely that these findings are secondary to an age-sensitive radiation-induced insult of the pituitary-hypothalamic axis. Two possible mechanisms have been suggested: leptin insensitivity and/or growth hormone deficiency. Radiation at a young age may affect the developing hypothalamus and result in leptin-receptor insensitivity. Leptin is a peptide hormone that is secreted by adipocytes (predominantly white adipose tissue).28,29 Circulating leptin levels are proportional to the total fat mass index; thus, the more obese an individual, the higher the leptin level. Leptin stimulates leptin receptors in the ventromedial hypothalamus, resulting in a decrease in food intake and an increase in energy expenditure. It has been hypothesized that this feedback between leptin, produced by the adipocytes, and the hypothalamus provides a mechanism for the body to sense and respond to alterations in energy balance and act as a satiety signal. Assessing the possible role of leptin-receptor insensitivity in radiation-associated obesity, Brennan et al30 evaluated 32 ALL survivors who had been treated with 18 to 25 Gy CRT (median age 17.8 years) and 35 age- and BMI-matched controls and reported that leptin levels were significantly higher in the leukemia survivors, with an increase in leptin per unit of fat mass. The differences were most marked for those with growth hormone deficiency (GHD; n = 9) and, to a lesser degree, those with insufficient growth hormone peaks (n = 12). Survivors with normal growth hormone stimulation did not have different leptin levels or a difference in leptin to fat mass in comparison with the controls. Alternatively, the radiation-associated changes may be mediated through alterations in growth hormone secretion. GHD in adulthood is associated with obesity.31 Adult survivors of childhood ALL who were treated with CRT are at increased risk for GHD.32 Whether GHD contributes to obesity in survivors is controversial. In an analysis of 50 childhood cancer survivors, including 28 ALL survivors, reduced spontaneous growth hormone secretion was associated with obesity.33 In contrast, Adan et al34 did not find a significant association between obesity and GHD in an analysis of 90 young adult cancer survivors (28 ALL survivors). It is also plausible that radiation damage to the more radiosensitive hypothalamus35,36 may result in both leptin-receptor insensitivity and, in some cases, varying degrees of GH insufficiency. Importantly, in contrast with a few smaller studies,5,7,8 this study did not find a significant association between treatment with chemotherapy only or lower-dose CRT (10 to 19 Gy) and overweight or obese survivors. It is important to note, however, that these previous studies evaluated survivors who were generally in their late childhood or adolescent years and used normative reference values for comparison. In this CCSS study, all participants were at least 18 years of age, with many survivors in their late 20s and early 30s, and they were compared with siblings of childhood cancer survivors. Little data are available that follow changes in BMI from diagnosis of ALL into adulthood. Thus, whether our findings reflect a normalization of previous weight gain with aging in survivors treated with chemotherapy only cannot be determined from this study. When interpreting the findings of this study, it is important to recognize several limitations. First, BMI was calculated from self-reported heights and weights, which are subject to a degree of imprecision. However, measurements of weight and height, even those reported by subjects themselves, are generally accurate and do not contribute significantly to errors in assessing BMI.37,38 In addition, bias in self-report should be similar for both the leukemia survivors and the sibling comparison groups. Second, a limitation of using BMI as a measure of body fat is that it does not distinguish fat mass from lean mass. More refined methods for estimation of fat mass, including bioimpedance and dual x-ray absorptiometry, may reveal additional risk in ALL survivors treated with chemotherapy only or lower-dose CRT. Nevertheless, BMI is the standard measure of obesity used in population-based studies, and increased BMI is strongly associated with cardiovascular disease, cancer, and all-cause mortality. Third, minority survivors were underrepresented in the sample with complete treatment and anthropometric data, limiting assessment of race and ethnicity as a modifier of outcomes. Finally, this study did not assess risk associated with more recent treatment protocols that include intensified regimens of intravenous methotrexate.
In summary, CRT
Childhood Cancer Survivor Study Institutions and Investigators
We thank John Whitton and Pauline Mitby for their assistance with the CCSS database.
Supported by grant 5U01-CA-55727-05 from the Department of Health and Human Services and funding to the University of Minnesota from the Childrens Cancer Research Fund. K.C. Oeffinger received partial support for this work through the American Academy of Family Physicians Advanced Research Training Grant.
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38. Stevens J, Keil JE, Waid LR, et al: Accuracy of current, 4-year, and 28-year self-reported body weight in an elderly population. Am J Epidemiol 132:11561163, 1990 Submitted June 21, 2002; accepted December 12, 2002. This article has been cited by other articles:
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