Comparability and representativeness of control groups in a case-control study of infant leukemia: a report from the Children's Oncology Group

Prospective investigation of folic acid supplements before and during early pregnancy and paediatric and adult cancers in the Chinese children and families cohort: a pilot study in a sample of rural and urban families

OBJECTIVE

To determine the feasibility of long-term prospective follow-up and ascertainment of cancer in offspring and mothers from the 1993-1995 Chinese Community Intervention Program that provided folic acid supplements before and during early pregnancy to reduce neural tube defects.

DESIGN

Feasibility pilot study for a prospective cohort study.

SETTING

Families residing during 2012-2013 in one rural and one urban county from 21 counties in 3 provinces in China included in the Community Intervention Program campaign.

PARTICIPANTS

The feasibility study targeted 560 families, including 280 from the rural and 280 from the urban county included in the large original study; about half of mothers in each group had taken and half had not taken folic acid supplements.

INTERVENTION

The planned new study is observational.

PRIMARY AND SECONDARY OUTCOME MEASURES

Primary: incidence of paediatric cancers in offspring; secondary: other chronic diseases in offspring and chronic diseases in mothers RESULTS: Only 3.4% of pilot study families could not be found, 3.9% had moved out of the study area and 8.8% refused to participate. Interviews were completed by 82% of mothers, 79% of fathers and 83% of offspring in the 560 families. Almost all mothers and offspring who were interviewed also participated in anthropometric measurements. We found notable urban-rural differences in sociodemographic and lifestyle characteristics of the parents, but fewer differences among the offspring. In eight catchment area hospitals, we identified a broad range of paediatric cancers diagnosed during 1994-2013, although paediatric brain tumours, lymphomas and rarer cancers were likely under-represented.

CONCLUSIONS

Overall, 20 years after the original Community Intervention Program, the pilot study achieved high levels of follow-up and family member interview participation, and identified substantial numbers of paediatric malignancies during 1994-2013 in catchment area hospitals. Next steps and strategies for overcoming limitations are described.

Socioeconomic Status and Childhood Cancer Incidence: A Population-Based Multilevel Analysis

The etiology of childhood cancers remains largely unknown, especially regarding environmental and behavioral risk factors. Unpacking the association between socioeconomic status (SES) and incidence may offer insight into such etiology. We tested associations between SES and childhood cancer incidence in a population-based case-cohort study (source cohort: Minnesota birth registry, 1989-2014). Cases, ages 0-14 years, were linked from the Minnesota Cancer Surveillance System to birth records through probabilistic record linkage. Controls were 4:1 frequency matched on birth year (2,947 cases and 11,907 controls). We tested associations of individual-level (maternal education) and neighborhood-level (census tract composite index) SES using logistic mixed models. In crude models, maternal education was positively associated with incidence of acute lymphoblastic leukemia (odds ratio (OR) = 1.10, 95% confidence interval (CI): 1.02, 1.19), central nervous system tumors (OR = 1.12, 95% CI: 1.04, 1.21), and neuroblastoma (OR = 1.15, 95% CI: 1.02, 1.30). Adjustment for established risk factors-including race/ethnicity, maternal age, and birth weight-substantially attenuated these positive associations. Similar patterns were observed for neighborhood-level SES. Conversely, higher maternal education was inversely associated with hepatoblastoma incidence (adjusted OR = 0.70, 95% CI: 0.51, 0.98). Overall, beyond the social patterning of established demographic and pregnancy-related exposures, SES is not strongly associated with childhood cancer incidence.

Cesarean Delivery and Risk of Infant Leukemia: A Report from the Children's Oncology Group

Background: Studies have reported increased risks of pediatric acute lymphoblastic leukemia (ALL) among children born by cesarean delivery (CD). However, no previous study has examined the impact of CD on risk of infant leukemia specifically.Methods: In this study, 443 infants diagnosed with acute leukemia, including both ALL and acute myelogenous leukemia (AML), were identified at Children's Oncology Group institutions between January 1996 and December 2006; 324 controls frequency matched by year of birth were identified though random digit dialing and random selection from U.S. birth registries. Using interview data and, for a subset of participants, medical record data, we analyzed CD overall and by indications that likely resulted in pre-labor CD (PLCD) or emergency CD (ECD). Odds ratios (ORs) and 95% confidence intervals (CIs) for risk of ALL and AML were estimated using multivariable unconditional logistic regression models, adjusted for year of birth, birth weight, and maternal race.Results: We observed an increased point estimate for the association between CD and ALL (OR, 1.52 and 95% CI, 1.02-2.25). We did not observe an association between CD and AML (OR, 1.02 and 95% CI, 0.64-1.62). In analyses of indication for CD, we observed elevated effect estimates for the associations of both PLCD and ECD and infant ALL.Conclusions: Our analysis suggests an increased risk of infant ALL following CD, including both PLCD and ECD. Altered microbiota colonization may be involved in development of leukemia in infants, but clear biological mechanisms have yet to be determined.Impact: This study provides the first in-depth examination of CD and infant leukemia. Cancer Epidemiol Biomarkers Prev; 27(4); 473-8. ©2018 AACR.

Evaluating the use of friend or family controls in epidemiologic case-control studies

BACKGROUND

Traditional methodologies for identifying and recruiting controls in epidemiologic case-control studies, such as random digit dialing or neighborhood walk, suffer from declining response rates. Here, we revisit the feasibility and comparability of using alternative sources of controls, specifically friend and family controls.

METHODS

We recruited from a recently completed case-control study of non-Hodgkin lymphoma (NHL) among women in Los Angeles County where controls from the parent study were ascertained by neighborhood walk. We calculated participation rates and compared questionnaire responses between the friend/family controls and the original matched controls from the parent study.

RESULTS

Of the 182 NHL case patients contacted, 111 (61%) agreed to participate in our feasibility study. 70 (63%) provided contact information for potential friend and/or family member controls. We were able to successfully contact and recruit a friend/family member for 92% of the case patients. This represented 46 friend controls and 54 family controls. Family controls significantly differed from original matched controls by sex and household income. Other characteristics were similar between friend controls and the original study's neighborhood controls.

CONCLUSION

The apparent comparability of neighborhood controls to friend and family controls among respondents in this study suggests that these alternative methods of control identification can serve as a complementary source of eligible controls in epidemiologic case-control studies.

Birthweight and Childhood Cancer: Preliminary Findings from the International Childhood Cancer Cohort Consortium (I4C)

BACKGROUND

Evidence relating childhood cancer to high birthweight is derived primarily from registry and case-control studies. We aimed to investigate this association, exploring the potential modifying roles of age at diagnosis and maternal anthropometrics, using prospectively collected data from the International Childhood Cancer Cohort Consortium.

METHODS

We pooled data on infant and parental characteristics and cancer incidence from six geographically and temporally diverse member cohorts [the Avon Longitudinal Study of Parents and Children (UK), the Collaborative Perinatal Project (USA), the Danish National Birth Cohort (Denmark), the Jerusalem Perinatal Study (Israel), the Norwegian Mother and Child Cohort Study (Norway), and the Tasmanian Infant Health Survey (Australia)]. Birthweight metrics included a continuous measure, deciles, and categories (≥ 4.0 vs. < 4.0 kilogram). Childhood cancer (377 cases diagnosed prior to age 15 years) risk was analysed by type (all sites, leukaemia, acute lymphoblastic leukaemia, and non-leukaemia) and age at diagnosis. We estimated hazard ratios (HR) and 95% confidence intervals (CI) from Cox proportional hazards models stratified by cohort.

RESULTS

A linear relationship was noted for each kilogram increment in birthweight adjusted for gender and gestational age for all cancers [HR = 1.26; 95% CI 1.02, 1.54]. Similar trends were observed for leukaemia. There were no significant interactions with maternal pre-pregnancy overweight or pregnancy weight gain. Birthweight ≥ 4.0 kg was associated with non-leukaemia cancer among children diagnosed at age ≥ 3 years [HR = 1.62; 95% CI 1.06, 2.46], but not at younger ages [HR = 0.7; 95% CI 0.45, 1.24, P for difference = 0.02].

CONCLUSION

Childhood cancer incidence rises with increasing birthweight. In older children, cancers other than leukaemia are particularly related to high birthweight. Maternal adiposity, currently widespread, was not demonstrated to substantially modify these associations. Common factors underlying foetal growth and carcinogenesis need to be further explored.

Accuracy of prenatal smoking data from Washington State birth certificates in a population-based sample with cotinine measurements

PURPOSE

To assess the accuracy of smoking data in contemporary U.S. birth certificates.

METHODS

We compared data on prenatal smoking as reported on Washington State birth certificates to cotinine measured in archived newborn screening dried blood spots for 200 infants born in 2007 (100 randomly selected from births to self-reported nonsmokers and 100 born to self-reported smokers). We estimated the sensitivity of the birth certificate data to identify prenatal smokers and the precision with which self-identified third trimester smokers report smoking levels.

RESULTS

Infants born to two (2%) mothers who reported they did not smoke during the pregnancy had whole blood cotinine concentrations consistent with active smoking by the mother (sensitivity 85%). Sensitivity of the birth certificate to identify reported smokers who continued to smoke throughout pregnancy was similar (89%). Among self-identified third trimester smokers whose infants' specimens were collected shortly after delivery, Spearman rho between infant cotinine and maternal-reported cigarettes/day in the third trimester was 0.54.

CONCLUSIONS

Birth certificates may represent a viable option for assessing prenatal smoking status, and possibly smoking cessation and level among smokers, in epidemiologic studies sufficiently powered to overcome a moderate amount of exposure measurement error.

Comparison of address-based sampling and random-digit dialing methods for recruiting young men as controls in a case-control study of testicular cancer susceptibility

Random-digit dialing (RDD) using landline telephone numbers is the historical gold standard for control recruitment in population-based epidemiologic research. However, increasing cell-phone usage and diminishing response rates suggest that the effectiveness of RDD in recruiting a random sample of the general population, particularly for younger target populations, is decreasing. In this study, we compared landline RDD with alternative methods of control recruitment, including RDD using cell-phone numbers and address-based sampling (ABS), to recruit primarily white men aged 18-55 years into a study of testicular cancer susceptibility conducted in the Philadelphia, Pennsylvania, metropolitan area between 2009 and 2012. With few exceptions, eligible and enrolled controls recruited by means of RDD and ABS were similar with regard to characteristics for which data were collected on the screening survey. While we find ABS to be a comparably effective method of recruiting young males compared with landline RDD, we acknowledge the potential impact that selection bias may have had on our results because of poor overall response rates, which ranged from 11.4% for landline RDD to 1.7% for ABS.

Predictors of mother and child DNA yields in buccal cell samples collected in pediatric cancer epidemiologic studies: a report from the Children's Oncology group

Background

Collection of high-quality DNA is essential for molecular epidemiology studies. Methods have been evaluated for optimal DNA collection in studies of adults; however, DNA collection in young children poses additional challenges. Here, we have evaluated predictors of DNA quantity in buccal cells collected for population-based studies of infant leukemia (N = 489 mothers and 392 children) and hepatoblastoma (HB; N = 446 mothers and 412 children) conducted through the Children’s Oncology Group. DNA samples were collected by mail using mouthwash (for mothers and some children) and buccal brush (for children) collection kits and quantified using quantitative real-time PCR. Multivariable linear regression models were used to identify predictors of DNA yield.

Results

Median DNA yield was higher for mothers in both studies compared with their children (14 μg vs. <1 μg). Significant predictors of DNA yield in children included case–control status (β = −0.69, 50% reduction, P = 0.01 for case vs. control children), brush collection type, and season of sample collection. Demographic factors were not strong predictors of DNA yield in mothers or children in this analysis.

Conclusions

The association with seasonality suggests that conditions during transport may influence DNA yield. The low yields observed in most children in these studies highlight the importance of developing alternative methods for DNA collection in younger age groups.

Children's Oncology Group's 2013 blueprint for research: epidemiology

Investigators worldwide have for over 40 years conducted case-control studies aimed at determining the causes of childhood cancer. The central challenge to conducting such research is the rarity of childhood cancer, thus many studies aggregate cases through clinical trials organizations such as COG. Rarity also precludes the use of prospective study designs, which are less prone to recall and selection biases. Despite these challenges a substantial literature on childhood cancer etiology has emerged but few strong environmental risk factors have been identified. Genetic studies are thus now coming to the fore with some success. The ultimate aim of epidemiologic studies is to reduce the population burden of childhood cancer by suggesting preventive measures or possibly by enabling early detection. Pediatr Blood Cancer 2013; 60: 1059-1062. © 2012 Wiley Periodicals, Inc.

Maternal prenatal cigarette, alcohol and illicit drug use and risk of infant leukaemia: a report from the Children's Oncology Group

Several case-control studies have evaluated associations between maternal smoking, alcohol consumption and illicit drug use during pregnancy and risk of childhood leukaemia. Few studies have specifically focused on infants (<1 year) with leukaemia, a group that is biologically and clinically distinct from older children. We present data from a Children's Oncology Group case-control study of 443 infants diagnosed with acute leukaemia [including acute lymphoblastic leukaemia (ALL) and acute myeloid leukaemia (AML)] between 1996 and 2006 and 324 population controls. Mothers were queried about their cigarette, alcohol and illicit drug use 1 year before and throughout pregnancy. Odds ratios (ORs) and 95% confidence intervals [CI] were calculated using adjusted unconditional logistic regression models. Maternal smoking (>1 cigarette/day) and illicit drug use (any amount) before and/or during pregnancy were not significantly associated with infant leukaemia. Alcohol use (>1 drink/week) during pregnancy was inversely associated with infant leukaemia overall [OR = 0.64; 95% CI 0.43, 0.94], AML [OR = 0.49; 95% CI 0.28, 0.87], and leukaemia with mixed lineage leukaemia gene rearrangements ('MLL+') [OR = 0.59; 95% CI 0.36, 0.97]. While our results agree with the fairly consistent evidence that maternal cigarette smoking is not associated with childhood leukaemia, the data regarding alcohol and illicit drug use are not consistent with prior reports and are difficult to interpret. It is possible that unhealthy maternal behaviours during pregnancy, some of which carry potential legal consequences, may not be adequately measured using only self-report. Future case-control studies of childhood leukaemia that pursue these exposures may benefit from incorporation of validated instruments and/or biomarkers when feasible.

Practical and analytical aspects of using friend controls in case-control studies: experience from a case-control study of childhood cancer

We report empirical data on the use of friend controls, specifically response rates, case-control concordance and analytical approaches. The data derive from a North American multi-institutional study of childhood cancer that was conducted in 2002-07 and that focused on paternal exposures. Case parents nominated friends as potential controls; up to three controls participated per case. For 137 (69%) of the 199 case families, at least one control parent participated. Of 374 potential controls contacted, 247 (66%) participated. Case fathers with controls were markedly more likely to be non-Hispanic White, college graduates and non-smokers compared with case fathers without controls. Odds ratios adjusted for demographic characteristics were generally similar but occasionally differed between analyses that included only members of matched sets and those that included all participants, i.e., controls and cases with and without controls. For demographic characteristics, simulations demonstrated that the observed concordance of cases and controls within matched sets exceeded that expected under random ascertainment, indicating probable overmatching. However, the observed concordance of smoking and other exposures was similar to the expectation under random ascertainment, suggesting little overmatching on exposures. Although not ideal, friend controls were convenient, had a reasonably high response rate and provided controls closely matched on race/ethnicity, education and age.

Maternal exposure to household chemicals and risk of infant leukemia: a report from the Children's Oncology Group

OBJECTIVE

Utilizing data from the largest study to date, we examined associations between maternal preconception/prenatal exposure to household chemicals and infant acute leukemia.

METHODS

We present data from a Children's Oncology Group case-control study of 443 infants (<1 year of age) diagnosed with acute leukemia [including acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML)] between 1996 and 2006 and 324 population controls. Mothers recalled household chemical use 1 month before and throughout pregnancy. We used unconditional logistic regression adjusted for birth year, maternal age, and race/ethnicity to calculate odds ratios (ORs) and 95% confidence intervals (CIs).

RESULTS

We did not find evidence for an association between infant leukemia and eight of nine chemical categories. However, exposure to petroleum products during pregnancy was associated with AML (OR = 2.54; 95% CI:1.40-4.62) and leukemia without mixed lineage leukemia (MLL) gene rearrangements ("MLL-") (OR = 2.69; 95% CI: 1.47-4.93). No associations were observed for exposure in the month before pregnancy.

CONCLUSIONS

Gestational exposure to petroleum products was associated with infant leukemia, particularly AML, and MLL- cases. Benzene is implicated as a potential carcinogen within this exposure category, but a clear biological mechanism has yet to be elucidated.

Analgesic use during pregnancy and risk of infant leukaemia: a Children's Oncology Group study

Background:

Infant leukaemia is likely initiated in utero.

Methods:

We examined whether analgesic use during pregnancy was associated with risk by completing telephone interviews of the mothers of 441 infant leukaemia cases and 323 frequency-matched controls, using unconditional logistic regression.

Results:

With the exception of a reduced risk for infant acute myeloid leukaemias with non-aspirin non-steroidal anti-inflammatory drugs (NSAID) use early in pregnancy (odds ratios=0.60; confidence intervals: 0.37–0.97), no statistically significant associations were observed for aspirin, non-aspirin NSAIDs, or acetaminophen use in early pregnancy or after knowledge of pregnancy.

Conclusion:

Overall, analgesic use during pregnancy was not significantly associated with the risk of infant leukaemia.

Childhood acute leukemia, early common infections, and allergy: The ESCALE Study

This study investigated the role of factors considered related to early stimulation of the immune system in the etiology of childhood acute leukemia. The national registry-based case-control study ESCALE was carried out in France in 2003-2004. Population controls were frequency matched to cases on age and gender. Data were obtained from structured telephone questionnaires administered to mothers. Odds ratios were estimated using unconditional regression models adjusted for potential confounders. Included were 634 acute lymphoblastic leukemia cases, 86 acute myeloblastic leukemia cases, and 1,494 controls aged ≥1 year. Negative associations were observed between acute lymphoblastic leukemia and birth order (P for trend < 0.0001), attendance at a day-care center before age 1 year (odds ratio (OR) = 0.8, 95% confidence interval (CI): 0.6, 1.1), prolonged breastfeeding (OR = 0.7, 95% CI: 0.5, 1.0), repeated early common infections (OR = 0.7, 95% CI: 0.6, 0.9), regular contact with farm animals (OR = 0.6, 95% CI: 0.5, 0.8), frequent farm visits in early life (OR = 0.4, 95% CI: 0.3, 0.6), and history of asthma (OR = 0.7, 95% CI: 0.4, 1.0) or eczema (OR = 0.7, 95% CI: 0.6, 0.9). Results support the hypothesis that repeated early infections and asthma may play a role against childhood acute leukemia.

Maternal vitamin and iron supplementation and risk of infant leukaemia: a report from the Children's Oncology Group

Background:

Prenatal supplementation has been inversely associated with childhood, but not with infant, leukaemia.

Methods:

Mothers of 443 cases of infant leukaemia diagnosed during 1996–2006 and 324 frequency-matched controls completed interviews. Associations were evaluated by unconditional logistic regression.

Results:

We observed no associations between prenatal vitamin (odds ratio (OR)=0.79, 95% confidence interval (CI): 0.44–1.42) or iron supplementation (OR=1.07, 95% CI: 0.75–1.52) and infant leukaemia after adjustment for race/ethnicity and income. Similar results were observed for leukaemia subtypes analysed separately.

Conclusion

The observed null associations may be attributable to high supplementation rates and/or national fortification programmes.

Infant leukemia and congenital abnormalities: a Children's Oncology Group study

BACKGROUND

Leukemia in infants is rare and has not been well studied apart from leukemia in older children. Differences in survival and the molecular characteristics of leukemia in infants versus older children suggest a distinct etiology, likely involving prenatal factors.

PROCEDURE

We examined the association between eight categories of maternally reported congenital abnormalities (CAs) (cleft lip or palate, spina bifida or other spinal defect, large or multiple birthmarks, other chromosomal abnormalities, small head or microcephaly, rib abnormalities, urogenital abnormalities, and other) and infant leukemia in a case-control study. The study included 443 cases diagnosed at <1 year of age at a Children's Oncology Group Institution in the United States or Canada from 1996 to 2006 and 324 controls. Controls were recruited from the cases' geographic area either by random digit dialing (1999-2002) or through birth certificates (2003-2008) and were frequency-matched to cases on birth year. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated by unconditional logistic regression after adjustment for birth year and a measure of follow-up time to account for differences in the CA observation period.

RESULTS

No statistically significant associations were observed between infant leukemia and any CA (OR = 1.2; 95% CI: 0.8-1.9), birthmarks (OR = 1.4; 95% CI: 0.7-2.5), urogenital abnormalities (OR = 0.7; 95% CI: 0.2-2.0), or other CA (OR = 1.4; 95% CI: 0.7-2.8). Results were similar for acute lymphoblastic and myeloid leukemia cases. Fewer than five subjects were in the remaining CA categories precluding analysis.

CONCLUSIONS

Overall, we did not find evidence to support an association between CAs and infant leukemia.

Infant leukemia and parental infertility or its treatment: a Children's Oncology Group report

BACKGROUND

Little is known about the potential risk factors for infant leukemia. With its very young age at diagnosis, exposures occurring in the perinatal period are suspected. Parental infertility and infertility treatment have been studied with regard to childhood cancer in general, but rarely in individual cancer subtypes.

METHODS

A case-control study of infant leukemia was conducted through the Children's Oncology Group, including cases diagnosed from January 1996 to December 2006 and controls selected through random digit dialing and birth certificate tracing. Maternal phone interviews were conducted to obtain information about infertility, infertility treatment and demographic factors. All cases as well as subgroups defined by mixed lineage leukemia (MLL) translocation status and leukemia subtype were examined. Statistical analysis was performed using multivariate logistic regression models.

RESULTS

No significant associations between infertility or its treatment and combined infant leukemia were found. In subgroup analyses, there was a significant increase in the risk of MLL--leukemia for children born to women not trying to conceive compared with those trying for <1 year for all types combined [odds ratio (OR) = 1.62, 95% confidence interval (CI) = 1.01-2.59] and for acute lymphoblastic leukemia (OR = 2.50, 95% CI = 1.36-4.61).

CONCLUSIONS

There were no positive associations between parental infertility or infertility treatment and infant leukemia. While this is the largest study to date, both selection and recall bias may have impacted the results. However, for infant leukemia, we can potentially rule out large increases in risk associated with parental infertility or its treatment.