Perinatal and reproductive factors: a report on haematological malignancies from the UKCCS

Effects of hypertension and use of antihypertensive drugs in pregnancy on the risks of childhood cancers in Taiwan

BACKGROUND

Childhood cancers are associated with high mortality and morbidity, and some maternal prescription drug use during pregnancy has been implicated in cancer risk. There are few studies on the effects of hypertension, preeclampsia, and the use of antihypertensives in pregnancy on children's cancer risks.

OBJECTIVE

This population-based cohort study analyzed the relationship between hypertension, preeclampsia, and antihypertensives taken during pregnancy and the risks of childhood cancers in the offspring.

METHODS

Data on all children born in Taiwan between 2004 and 2015 (N = 2,294,292) were obtained from the Maternal and Child Health Database. This registry was linked with the National Health Insurance Database and Cancer Registry to get the records of maternal use of diuretics or other antihypertensives in pregnancy and records of children with cancer diagnosed before 13 years. We used Cox proportional hazard modeling to estimate the influence of maternal health conditions and antihypertensive drug exposure on the risks of developing childhood cancers.

RESULTS

Offspring of mothers with hypertension (chronic or gestational) had a higher risk of acute lymphocytic lymphoma [hazard ratio (HR) = 1.87, 95% Confidence Interval (CI) 1.32 - 2.65] and non-Hodgkin's lymphoma (HR = 1.96, 95% CI 1.34 - 2.86). We estimated only a weak increased cancer risk in children whose mothers used diuretics (HR = 1.16, 95% CI 0.77 - 1.74) or used antihypertensives other than diuretics (HR = 1.15, 95% CI 0.86 - 1.54) before birth.

CONCLUSIONS

In this cohort study, children whose mothers had chronic and gestational hypertension had an increased risk of developing childhood cancer.

Preeclampsia, antihypertensive medication use in pregnancy and risk of childhood cancer in offspring

PURPOSE

Preeclampsia is a serious pregnancy complication that presents a significant risk to both the mother and the fetus. Preeclampsia and medications associated with its treatment are potentially linked to increased childhood cancer risk. Therefore, we examined the association between preeclampsia, antihypertensive medications, and childhood cancer in offspring.

METHODS

Cases (n = 6,420) and controls (n = 160,484) were obtained from Danish national registries. We performed conditional logistic regression analyses to estimate the association between preeclampsia and childhood cancer risk, and examined the effects of antihypertensive medication use in pregnancy in relation to childhood cancer risk in the offspring with adjustment for relevant covariates.

RESULTS

We observed an increased risk of acute lymphoblastic leukemia (ALL) among those whose mothers had preeclampsia (OR = 1.36, 95% CI 1.03, 1.79), especially for severe preeclampsia (OR = 2.36, 95% CI 1.37, 4.08). We also estimated an increased cancer risk in children born to mothers who were prescribed diuretics during pregnancy [OR = 2.09, 95% confidence interval (CI) 1.39, 3.14]. Intake of other antihypertensive medications was not associated with childhood cancer (OR = 0.78, 95% CI 0.50, 1.23). Among women who did not take diuretics in pregnancy, preeclampsia was associated with neuroblastoma (OR = 2.22, 95% CI 1.08, 4.55).

CONCLUSION

Our findings suggested an increased risk for certain types of cancer in the offspring of mothers with preeclampsia and an increased risk of cancer with diuretic intake during pregnancy.

Hyperemesis gravidarum and the risk of childhood cancer - A case-control study in Denmark

OBJECTIVE

Only a few studies have reported on the association between hyperemesis gravidarum and the risk of childhood cancer. We examined possible associations in this population-based study in Denmark.

METHODS

Pediatric cancer cases (n = 6420) were ascertained from the Denmark Cancer Registry among children born between 1977 and 2013. Twenty-five controls were matched to each case by sex and birth date from the Central Person Registry (n = 160500). Mothers with hyperemesis gravidarum were ascertained from the National Patient Register. The risk of childhood cancer was estimated using conditional logistic regression. In a separate analysis, we examined pregnancy prescription of antinauseant medications, ascertained from the National Pharmaceutical Register, to determine associations with childhood cancers.

RESULTS

In Denmark, hyperemesis gravidarum was associated with an increased risk of childhood cancer [all types combined; Odds Ratio (OR) = 1.43, 95% confidence interval (CI) 1.12, 1.81; n = 73 exposed cases). Hyperemesis gravidarum was also associated with an increased risk of neuroblastoma (OR = 2.52, 95% CI 1.00, 6.36; n = 5 exposed cases), acute lymphoblastic leukemia (OR = 1.63, 95% CI 0.98, 2.72; n = 16 exposed cases), and non-Hodgkin's lymphoma (OR = 2.41, 95% CI 0.95, 6.08; n = 5 exposed cases). We observed no childhood cancer risk increase from antinauseant prescriptions (OR = 1.05, 95% CI 0.84, 1.30; n = 91 exposed cases).

CONCLUSION

Our results are suggestive of an association between hyperemesis gravidarum and the overall cancer risk in offspring, particularly for neuroblastoma. Mothers with hyperemesis gravidarum should be closely monitored and receive appropriate treatment during pregnancy.

Cohort profile: the United Kingdom Childhood Cancer Study (UKCCS) - a UK-wide population-based study examining the health of cancer survivors

PURPOSE

The United Kingdom Childhood Cancer Study's (UKCCS's) matched cohort was established to examine the longer term morbidity and mortality of individuals previously diagnosed with cancer before 15 years of age, comparing future healthcare patterns in 5-year cancer survivors to baseline activity seen in age- and sex-matched individuals from the general population.

PARTICIPANTS

Predicated on a national childhood cancer case-control study conducted in the early 1990s (4430 cases, 9753 controls) in England, Scotland and Wales, the case population comprises 3125 cancer survivors (>5 years), and the control population 7156 age- and sex-matched individuals from the general population who did not have cancer as a child. Participants are now being followed up via linkage to national administrative healthcare databases (deaths, cancers and secondary care hospital activity).

FINDINGS TO DATE

Enabling the creation of cohorts with minimal selection bias and loss to follow-up, the original case-control study registered all newly diagnosed cases of childhood cancer and their corresponding controls, regardless of their family's participation. Early findings based on the registered case population found marked survival variations with age and sex across subtypes and differences with deprivation among acute lymphoblastic leukaemia (ALL) survivors. More recently, comparing the health-activity patterns of the case and control populations revealed that survivors of childhood ALL experienced excess outpatient and inpatient activity across their teenage/young adult years. Adding to increased risks of cancer and death and involving most clinical specialties, excesses were not related to routine follow-up monitoring and showed no signs of diminishing over time.

FUTURE PLANS

With annual linkage updates, the UKCCS's maturing population-based matched cohorts provide the foundation for tracking the health of individuals through their lifetime. Comparing the experience of childhood cancer survivors to that of unaffected general-population counterparts, this will include examining subsequent morbidity and mortality, secondary care hospital activity and the impact of deprivation on longer term outcomes.

Maternal and perinatal outcomes following a diagnosis of Hodgkin lymphoma during or prior to pregnancy: A systematic review

BACKGROUND

The initial peak incidence of Hodgkin lymphoma (HL) occurs during reproductive years.

OBJECTIVES

Synthesise published literature on the relationship between HL and maternal and perinatal outcomes.

SEARCH STRATEGY

Systematic search of PubMed/Medline, Cochrane Library, Scopus, Embase and Science Direct from inception to June 2022, supplemented by hand-searching reference lists.

SELECTION CRITERIA

Two reviewers independently reviewed titles, abstracts and full-text articles. Published studies containing original data were eligible.

DATA COLLECTION AND ANALYSIS

Two reviewers independently extracted data and appraised study quality. Outcomes for pregnant women with a previous/current diagnosis of HL were compared separately with women never diagnosed with HL. Where data permitted, meta-analyses of odds ratios and proportions were performed. Certainty of evidence was determined using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) framework.

MAIN RESULTS

Of the 5527 studies identified, 33 met the inclusion criteria. In the groups with HL before pregnancy and HL during pregnancy, adjusted odds ratios were not statistically significant for congenital malformation (aOR 1.7, 95% CI 0.9-3.1, and aOR 1.84, 95% CI 0.81-4.15, respectively), preterm birth (PTB) (aOR 0.99, 95% CI 0.65-1.51, and aOR 6.74, 95% CI 0.52-88.03, respectively) and miscarriage (aOR 0.78, 95% CI 0.55-1.10, and aOR 0.38, 95% CI 0.05-2.72, respectively). The aORs for all other outcomes were not statistically significant, except for blood transfusion (aOR 1.38, 95% CI 1.05-1.82) and venous thromboembolism (VTE) (aOR 7.93, 95% CI 2.97-21.22) in the group for HL during pregnancy. The proportion of anaemia was also increased in this group (69%, 95% CI 57%-80% vs 4%, 95% CI 4%-5%, respectively). The GRADE certainty of findings ranged from low to very low.

CONCLUSIONS

Rates of most adverse pregnancy outcomes among women with a previous/current HL diagnosis are not increased significantly compared with the general pregnant population. Women with HL diagnosed during pregnancy may have a higher PTB rate and increased likelihood of VTE, anaemia and blood transfusion; however, small study numbers and the low to very low GRADE certainty of findings preclude firm conclusions.

Maternal anemia and the risk of childhood cancer: A population-based cohort study in Taiwan

BACKGROUND

Childhood cancer may be related to maternal health in pregnancy. Maternal anemia is a common condition in pregnancy, especially in low-income countries, but the association between maternal anemia and childhood cancer has not been widely studied.

OBJECTIVE

To examine the potential relation between maternal anemia during pregnancy and childhood cancers in a population-based cohort study in Taiwan.

METHODS

We examined the relationship between maternal anemia and childhood cancer in Taiwan (N = 2160 cancer cases, 2,076,877 noncases). Cases were taken from the National Cancer Registry, and noncases were selected from birth records. Using national health registries, we obtained maternal anemia diagnoses. We estimated the risks for childhood cancers using Cox proportional hazard analysis.

RESULTS

There was an increased risk of cancers in children born to mothers with nutritional anemia (hazard ratio (HR): 1.32, 95% CI 0.99, 1.76). Iron deficiency anemia (HR: 1.30, 95% CI 0.97-1.75) carried an increased risk, while non-nutritional anemias were not associated with childhood cancer risk.

CONCLUSION

Our results provide additional support for screening for anemia during pregnancy. Adequate nutrition and vitamin supplementation may help to prevent some childhood cancer.

Maternal anemia and childhood cancer: a population-based case-control study in Denmark

BACKGROUND

Childhood cancer risk is associated with maternal health during pregnancy. Anemia in pregnancy is a common condition, especially in low-income countries, but a possible association between maternal anemia and childhood cancer has not been widely studied.

METHODS

We examined the relation in a population-based study in Denmark (N = 6420 cancer cases, 160,485 controls). Cases were taken from the Danish Cancer Registry, and controls were selected from national records. We obtained maternal anemia diagnoses from the National Patient and Medical Births registries. In a separate analysis within the years available (births 1995-2014), we examined cancer risks among mothers taking prescribed vitamin supplements, using data from the National Prescription Register. We estimated the risks of childhood cancer using conditional logistic regression.

RESULTS

The risks of neuroblastoma [odds ratio (OR= 1.83, 95% confidence interval (CI): 1.04, 3.22] and acute lymphoblastic leukemia (OR= 1.46, 95% CI 1.09, 1.97) were increased in children born to mothers with anemia in pregnancy. There was a two-fold increased risk for bone tumors (OR= 2.59, 95% CI: 1.42, 4.72), particularly osteosarcoma (OR= 3.54, 95% CI 1.60, 7.82). With regards to prescribed supplement use, mothers prescribed supplements for B12 and folate deficiency anemia (OR= 4.03, 95% CI 1.91, 8.50) had an increased risk for cancer in offspring.

CONCLUSION

Our results suggest that screening for anemia in pregnancy and vitamin supplementation may be an actionable strategy to prevent some cases of childhood cancer.

Evaluation of Maternal Infection During Pregnancy and Childhood Leukemia Among Offspring in Denmark

IMPORTANCE

Maternal infection is common during pregnancy and is an important potential cause of fetal genetic and immunological abnormalities. Maternal infection has been reported to be associated with childhood leukemia in previous case-control or small cohort studies.

OBJECTIVE

To evaluate the association of maternal infection during pregnancy with childhood leukemia among offspring in a large study.

DESIGN, SETTING, AND PARTICIPANTS

This population-based cohort study used data from 7 Danish national registries (including the Danish Medical Birth Register, the Danish National Patient Registry, the Danish National Cancer Registry, and others) for all live births in Denmark between 1978 and 2015. Swedish registry data for all live births between 1988 and 2014 were used to validate the findings for the Danish cohort. Data were analyzed from December 2019 to December 2021.

EXPOSURES

Maternal infection during pregnancy categorized by anatomic locations identified from the Danish National Patient Registry.

MAIN OUTCOMES AND MEASURES

The primary outcome was any leukemia; secondary outcomes were acute lymphoid leukemia (ALL) and acute myeloid leukemia (AML). Offspring childhood leukemia was identified in the Danish National Cancer Registry. Associations were first assessed in the whole cohort using Cox proportional hazards regression models, adjusted for potential confounders. A sibling analysis was performed to account for unmeasured familial confounding.

RESULTS

This study included 2 222 797 children, 51.3% of whom were boys. During the approximately 27 million person-years of follow-up (mean [SD], 12.0 [4.6] years per person), 1307 children were diagnosed with leukemia (ALL, 1050; AML, 165; or other, 92). Children born to mothers with infection during pregnancy had a 35% increased risk of leukemia (adjusted hazard ratio [HR], 1.35 [95% CI, 1.04-1.77]) compared with offspring of mothers without infection. Maternal genital and urinary tract infections were associated with a 142% and 65% increased risk of childhood leukemia, with HRs of 2.42 (95% CI, 1.50-3.92) and 1.65 (95% CI, 1.15-2.36), respectively. No association was observed for respiratory tract, digestive, or other infections. The sibling analysis showed comparable estimates to the whole-cohort analysis. The association patterns for ALL and AML were similar to that for any leukemia. No association was observed for maternal infection and brain tumors, lymphoma, or other childhood cancers.

CONCLUSIONS AND RELEVANCE

In this cohort study of approximately 2.2 million children, maternal genitourinary tract infection during pregnancy was associated with childhood leukemia among offspring. If confirmed in future studies, our findings may have implications for understanding the etiology and developing preventive measures for childhood leukemia.

A review of the types of childhood cancer associated with a medical X-ray examination of the pregnant mother

PURPOSE

For 65 years the interpretation of the statistical association between the risk of cancer in a child and a prior diagnostic X-ray examination of the abdomen of the pregnant mother has been debated. The objections to a direct cause-and-effect explanation of the association vary in their strength, but one of the most notable grounds for controversy is the finding from the first and largest case-control study reporting the association, the Oxford Survey of Childhood Cancers (OSCC), of an almost uniformly raised relative risk (RR) for nearly all of the types of cancer that are most frequent in children. Here we compare the antenatal X-ray associations found in the OSCC for different types of childhood cancer with the results of all other case-control and case-cohort studies appropriately combined in meta-analyses, and we also review the findings of the few cohort studies that have been conducted.

CONCLUSIONS

From the case-control/case-cohort studies other than the OSCC there are consistent and clear elevations of risk for all types of childhood cancer combined, all leukemia, and all cancers except leukemia combined. This compatibility of the findings of the OSCC with those of the combined other studies is less clear, or effectively absent, when some categories containing smaller numbers of incident cases/deaths are considered, but lack of precision of risk estimates due to sparse data presents inferential challenges, although there is a consistent absence of an association for bone tumors. Further, more recent studies almost certainly address lower intrauterine doses, with an anticipated decrease in estimated risks, which could be misleading when comparisons involve a limited number of studies that are mainly from later years, and a similar problem arises when having to employ all types of antenatal X-ray exposures for a study because data for abdominal exposures are absent. The problem of low statistical power is greater for cohort studies, and this, together with other shortcomings identified in the studies, limits the interpretational value of results. The findings of non-medical intrauterine exposure studies are constrained by sparse data and make a limited contribution to an understanding of the association. Certain aspects of the various studies require a need for caution in interpretation, but overall, the appropriate combination of all case-control/case-cohort studies other than the OSCC lends support to the inference that low-level exposure to radiation in utero proportionally increases the risk of the typical cancers of childhood to around the same level.

Early life ionizing radiation exposure and cancer risks: systematic review and meta-analysis

BACKGROUND

Ionizing radiation use for medical diagnostic purposes has substantially increased over the last three decades. Moderate to high doses of radiation are well established causes of cancer, especially for exposure at young ages. However, cancer risk from low-dose medical imaging is debated.

OBJECTIVE

To review the literature on cancer risks associated with prenatal and postnatal medical diagnostic ionizing radiation exposure among children and to assess this risk through a meta-analysis.

MATERIALS AND METHODS

A literature search of five electronic databases supplemented by a hand search was performed to retrieve relevant epidemiological studies published from 2000 to 2019, including patients younger than 22 years of age exposed to medical imaging ionizing radiation. Pooled odds ratio (OR_pooled) and pooled excess relative risk (ERR_pooled) representing the excess of risk per unit of organ dose were estimated with a random effect model.

RESULTS

Twenty-four studies were included. For prenatal exposure (radiographs or CT), no significant increased risk was reported for all cancers, leukemia and brain tumors. For postnatal exposure, increased risk was observed only for CT, mostly for leukemia (ERR_pooled=26.9 Gy^-1; 95% confidence interval [CI]: 2.7-57.1) and brain tumors (ERR_pooled=9.1 Gy^-1; 95% CI: 5.2-13.1).

CONCLUSION

CT exposure in childhood appears to be associated with increased risk of cancer while no significant association was observed with diagnostic radiographs.

Paediatric acute lymphoblastic leukaemia and caesarean section: A report from the United Kingdom Childhood Cancer Study (UKCCS)

BACKGROUND

Reports have suggested that children born by caesarean initiated before labour onset may be at increased risk of developing acute lymphoblastic leukaemia (ALL). However, with most data being derived from case-control study interviews, information on the underpinning reasons for caesarean section is sparse, and evidence is conflicting.

OBJECTIVES

Use clinical records compiled at the time of delivery to investigate the association between childhood ALL and caesarean delivery; examining timing in relation to labour onset, and reasons for the procedure.

METHODS

Data are from the UK Childhood Cancer Study, a population-based case-control study conducted in the 1990s, when caesarean section rates were relatively low, in England, Scotland, and Wales. Children with ALL were individually matched to two controls on sex, date of birth, and region of residence. Information on mode of delivery and complications was abstracted from obstetric records. Odds ratios (OR) and 95% confidence intervals (CI) were calculated using logistic regression models adjusted for matching variables and relevant covariates.

RESULTS

Around 75% of the 1034 cases and 1914 controls were born through unassisted vaginal delivery. Caesarean delivery was as frequent in cases and controls (OR 1.07, 95% CI 0.84, 1.36). No association was observed between ALL and caesarean delivery either during or before labour, with adjusted ORs of 1.08 (95% CI 0.78, 1.48) and 1.09 (95% CI 0.78, 1.53), respectively. For B-cell ALL, the ORs were 1.14 (95% CI 0.81, 1.59) for caesarean during labour and 1.21 (95% CI 0.85, 1.72) for prelabour. The underpinning reasons for caesarean delivery differed between cases and controls; with preeclampsia, although very rare, being more common amongst cases born by caesarean (OR 8.91, 95% CI 1.48, 53.42).

CONCLUSIONS

Our obstetric record-based study found no significant evidence that caesarean delivery increased the risk of childhood ALL, either overall or when carried out before labour.

Nausea and vomiting of pregnancy and hyperemesis gravidarum

Nausea and vomiting of pregnancy (NVP) is a common condition that affects as many as 70% of pregnant women. Although no consensus definition is available for hyperemesis gravidarum (HG), it is typically viewed as the severe form of NVP and has been reported to occur in 0.3-10.8% of pregnant women. HG can be associated with poor maternal, fetal and child outcomes. The majority of women with NVP can be managed with dietary and lifestyle changes, but more than one-third of patients experience clinically relevant symptoms that may require fluid and vitamin supplementation and/or antiemetic therapy such as, for example, combined doxylamine/pyridoxine, which is not teratogenic and may be effective in treating NVP. Ondansetron is commonly used to treat HG, but studies are urgently needed to determine whether it is safer and more effective than using first-line antiemetics. Thiamine (vitamin B1) should be introduced following protocols to prevent refeeding syndrome and Wernicke encephalopathy. Recent advances in the genetic study of NVP and HG suggest a placental component to the aetiology by implicating common variants in genes encoding placental proteins (namely GDF15 and IGFBP7) and hormone receptors (namely GFRAL and PGR). New studies on aetiology, diagnosis, management and treatment are under way. In the next decade, progress in these areas may improve maternal quality of life and limit the adverse outcomes associated with HG.

Birth Weight and Risk of Childhood Acute Lymphoblastic Leukemia in Arizona, Illinois, and Kentucky

OBJECTIVE

To confirm the previously reported increased risk of leukemia among macrosomic children (those with birth weight >4 kg).

METHODS

Birth certificates of Arizona, Illinois, and Kentucky children diagnosed as having acute lymphoblastic leukemia (ALL) before age 5 years were matched with birth certificates from leukemia-free children of the same sex, race, and ethnicity who were born in the same county on or about the same day. Odds ratios (ORs) for ALL among children of low (<2.5 kg) or high (>4 kg) birth weight were calculated by conditional logistic regression.

RESULTS

Children with high birth weight had an elevated risk of ALL in the first 5 years of life (OR 1.28, 95% confidence interval [CI] 1.01-1.61). The excess risk was confined to non-Hispanic whites (OR 1.77, 95% CI 1.27-2.48), both boys (OR 1.57, 95% CI 1.01-2.45) and girls (OR 2.10, 95% CI 1.26-3.52).

CONCLUSIONS

This study confirms the association between high birth weight and ALL previously reported by other studies in children of European ancestry. The literature on maternal risk factors for both macrosomia and ALL is reviewed, with maternal overnutrition emerging as a plausible risk factor for both outcomes.

Advancing Parental Age and Risk of Solid Tumors in Children: A Case-Control Study in Peru

Background

The causes of childhood cancer are not well known, but the advanced age of the parents has been suggested as a risk factor for childhood cancer in several observational studies. In this study, we examine a possible link between parental age and childhood solid tumors.

Methods

We conducted a hospital-based case-control study (310 cases and 620 controls, matched by age and gender) at Rebagliati Hospital, Lima, Peru. Odd ratio was used to compare categories of advancing maternal and paternal age with and without adjusting for possible confounding factors were calculated.

Results

The risk of childhood retinoblastoma was significantly higher among children of mothers aged> 35 years (adjusted OR 1.21; 95% CI, 1.09-6.08) and fathers aged> 35 years (OR 1.17; 1.01-16.33). A significant trend with increasing mother's age (p = 0.037) and father's age (p = 0.005) was found. There were more risks to development of non-Hodgkin's lymphoma (p = 0.047) and gonadal germ cell tumors (p = 0.04) for advanced paternal age. There was a strong protective effect of increasing parity on risk of solid tumors in children (p=0.0015).

Conclusion

Our results suggest that advanced parental age is associated with the risk for the development of retinoblastoma. Advanced paternal age increases the risk of non-Hodgkin lymphoma and gonadal germ cell tumor. The higher the order of birth of the children, the less the chance of developing any neoplasm.

Maternal anemia during pregnancy and slightly higher risk of asthma in male offspring

AIM

We aimed to determine whether maternal hemoglobin levels or anemia during pregnancy are associated with the development of asthma among offspring.

METHODS

Data were retrieved from the birth register database of Kuopio University Hospital between 1989 and 2007 (n = 38 381). Hemoglobin levels were measured during three trimesters of pregnancy and anemia was defined according to the World Health Organization criteria. The prevalence of asthma was determined from the register of reimbursement for medication for asthma at the Finnish Social Security Institution. Cox proportional hazard regression analysis was performed to evaluate the possible associations between prenatal factors and development of asthma ever.

RESULTS

A total of 8198 (21.4%) women had anemia at some stage of pregnancy. Mild maternal anemia during the first trimester was associated with an increased risk of asthma among male offspring (adjusted hazard ratio, 1.46; 95% confidence interval, 1.11-1.94) compared with those with normal maternal hemoglobin levels. This finding remained significant also after applying the Bonferroni correction.

CONCLUSION

Male offspring with maternal anemia during the first trimester of pregnancy had significantly more asthma ever than the offspring of women with normal hemoglobin levels during pregnancy. These findings were not strong but suggest possible sex-specific effects of maternal health on prenatal programming and future risk of asthma.

Parental Age and Risk of Lymphoid Neoplasms

High parental age at childbirth has repeatedly been linked to childhood malignancies, while few studies have focused on the offspring's risk of adult cancer. In this population-based case-control study, we identified 32,000 patients with lymphoid neoplasms, diagnosed at ages 0-79 years during the period 1987-2011, and 160,000 matched controls in Sweden. Using prospectively registered data on their first-degree relatives, we evaluated the impact of parental age on the risk of lymphoid neoplasms by subtype. Overall, each 5-year increment in maternal age was associated with a 3% increase in incidence of offspring lymphoid neoplasms (hazard ratio = 1.03, 95% confidence interval: 1.02, 1.04). The association was similar for paternal age and present even among individuals older than 70 years of age at diagnosis. Stratified analyses further revealed that the association was limited to certain subtypes, mostly of indolent nature. Risks of chronic lymphocytic leukemia, follicular lymphoma, and mantle cell lymphoma were 5%-10% higher per 5-year increment in maternal age, but no associations were observed for acute lymphoblastic leukemia, plasma cell neoplasms, or diffuse large B-cell lymphoma. These findings indicated that prenatal genetic or epigenetic changes influence risk of adult lymphoid neoplasms and suggest a difference in this association between aggressive and indolent lymphoma subtypes.

Maternal fetal loss history and increased acute leukemia subtype risk in subsequent offspring: a systematic review and meta-analysis

PURPOSE

History of fetal loss including miscarriage and stillbirth has been inconsistently associated with childhood (0-14 years) leukemia in subsequent offspring. A quantitative synthesis of the inconclusive literature by leukemia subtype was therefore conducted.

METHODS

Eligible studies (N = 32) were identified through the screening of over 3500 publications. Random-effects meta-analyses were conducted on the association of miscarriage/stillbirth history with overall (AL; 18,868 cases/35,685 controls), acute lymphoblastic (ALL; 16,150 cases/38,655 controls), and myeloid (AML; 3042 cases/32,997 controls) leukemia. Sensitivity and subgroup analyses by age and ALL subtype, as well as meta-regression were undertaken.

RESULTS

Fetal loss history was associated with increased AL risk [Odds Ratio (OR) 1.10, 95% Confidence Intervals (CI) 1.04-1.18]. The positive association was seen for ALL (OR 1.12, 95%CI 1.05-1.19) and for AML (OR 1.13, 95%CI 0.91-1.41); for the latter the OR increased in sensitivity analyses. Notably, stillbirth history was significantly linked to ALL risk (OR 1.33, 95%CI 1.02-1.74), but not AML. By contrast, the association of ALL and AML with previous miscarriage reached marginal significance. The association of miscarriage history was strongest in infant ALL (OR 2.34, 95%CI 1.19-4.60).

CONCLUSIONS

In this meta-analysis involving >50,000 children, we found noteworthy associations by indices of fetal loss, age at diagnosis, and leukemia type; namely, of stillbirth with ALL and miscarriage history with infant ALL. Elucidation of plausible underlying mechanisms may provide insight into leukemia pathogenesis and indicate monitoring interventions prior to and during pregnancy.

Maternal Preeclampsia and Odds of Childhood Cancers in Offspring: A California Statewide Case-Control Study

BACKGROUND

Preeclampsia is a major cause of adverse effects on fetal health. We examined associations between fetal exposure to preeclampsia and subsequent odds of childhood cancers.

METHODS

We obtained childhood cancer cases (n = 13 669) diagnosed at 5 years old or younger between 1988 and 2012 from the California Cancer Registry and linked them to birth certificates. Controls (n = 271 383) were randomly selected from all California births and frequency matched to cases by birth year. We obtained data regarding preeclampsia during pregnancy, labour, and delivery from the medical worksheet of the electronic birth record. We used unconditional logistic regression models with stabilised inverse probability weights to estimate the effect of preeclampsia on each subtype of childhood cancer, taking into account potential confounding by pregnancy characteristics. Marginal structural models were fitted to assess the controlled direct effects of preeclampsia, independent of preterm delivery and NICU admission.

RESULTS

Although a null association was observed for all cancer subtypes combined (odds ratio (OR) 1.0, 95% confidence interval (CI) 0.9, 1.2), preeclampsia was found to be associated with increased odds of two histological subtypes of germ cell tumours: seminomas (OR 8.6, 95% CI 1.9, 38.4) and teratoma (OR 3.0, 95% CI 1.7, 5.4), but not yolk sac tumours in children. Odds remained elevated after adjusting for preterm delivery and NICU admission. Increases in odds were also observed for hepatoblastoma, however this association was attenuated in marginal structural models after accounting for NICU admission.

CONCLUSIONS

These findings suggest that maternal preeclampsia is associated with higher odds of some rare childhood cancers and may shed light on new aetiological factors for these cancers.

Birth weight and risk of paediatric Hodgkin lymphoma: Findings from a population-based record linkage study in California

OBJECTIVE

To evaluate the relationship between birth weight (along with a variety of pre and perinatal characteristics) and the risk of paediatric Hodgkin lymphoma (HL) diagnosed at age <20 years.

METHOD

We linked California statewide birth records from 1978-2009 and cancer diagnosis data from 1988-2011 to conduct a population-based case-control study with 1216 cases and 4485 controls (matched on birth month and year, sex, and race/ethnicity). Conditional logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (95% CI) of paediatric HL overall and by age of diagnosis, controlling for other perinatal factors.

RESULTS

Compared to children with a normal birth weight (2500-3999 g), those who had a high birth weight (≥4000 g) had an increased risk of paediatric HL overall (OR = 1.23, 95% CI: 1.02-1.48) after adjusting for birth order, maternal age at the time of delivery, and paternal age at the time of delivery. The magnitude of association appeared larger for subgroups of children whose age of diagnosis was 0-10 years (OR = 1.56, 95% CI: 1.04-2.24) or 15-19 years (OR = 1.43, 95% CI: 1.11-1.83), while no association was observed in 11-14 year olds. Compared with firstborn children, those who were third or higher in birth order had a reduced risk of paediatric HL overall (OR = 0.80, 95% CI: 0.67-0.95), and this association also varied by age of diagnosis.

CONCLUSIONS

In this study with the largest number of paediatric HL cases, high birth weight was associated with an increased disease risk for most but not all ages of diagnosis. The different findings by age of diagnosis regarding both birth weight and birth order underscore the importance to stratify paediatric HL by age at diagnosis in future etiological investigations.

Environmental, maternal, and reproductive risk factors for childhood acute lymphoblastic leukemia in Egypt: a case-control study

BACKGROUND

Acute lymphocytic leukemia (ALL) is the most common pediatric cancer. The exact cause is not known in most cases, but past epidemiological research has suggested a number of potential risk factors. This study evaluated associations between environmental and parental factors and the risk for ALL in Egyptian children to gain insight into risk factors in this developing country.

METHODS

We conducted a case-control design from May 2009 to February 2012. Cases were recruited from Children's Cancer Hospital, Egypt (CCHE). Healthy controls were randomly selected from the general population to frequency-match the cumulative group of cases by sex, age groups (<1; 1 - 5; >5 - 10; >10 years) and region of residence (Cairo metropolitan region, Nile Delta region (North), and Upper Egypt (South)). Mothers provided answers to an administered questionnaire about their environmental exposures and health history including those of the father. Odds ratios (ORs) and 95 % confidence intervals (CI) were calculated using logistic regression with adjustment for covariates.

RESULTS

Two hundred ninety nine ALL cases and 351 population-based controls frequency-matched for age group, gender and location were recruited. The risk of ALL was increased with the mother's use of medications for ovulation induction (ORadj = 2.5, 95 % CI =1.2 -5.1) and to a lesser extend with her age (ORadj = 1.8, 95 % CI = 1.1 - 2.8, for mothers ≥ 30 years old). Delivering the child by Cesarean section, was also associated with increased risk (ORadj = 2.01, 95 % CI =1.24-2.81).

CONCLUSIONS

In Egypt, the risk for childhood ALL appears to be associated with older maternal age, and certain maternal reproductive factors.

Hyperemesis gravidarum and risk of cancer in offspring, a Scandinavian registry-based nested case-control study

BACKGROUND

Hyperemesis gravidarum is a serious condition affecting 0.8-2.3% of pregnant women and can be regarded as a restricted period of famine. Research concerning potential long-term consequences of the condition for the offspring, is limited, but lack of nutrition in-utero has been associated with chronic disease in adulthood, including some cancers. There is growing evidence that several forms of cancer may originate during fetal life. We conducted a large study linking the high-quality population-based medical birth- and cancer registries in Norway, Sweden and Denmark, to explore whether hyperemesis is associated with increased cancer risk in offspring.

METHODS

A registry-based nested case-control study. Twelve types of childhood cancer were selected; leukemia, lymphoma, cancer of the central nervous system, testis, bone, ovary, breast, adrenal and thyroid gland, nephroblastoma, hepatoblastoma and retinoblastoma. Conditional logistic regression models were applied to study associations between hyperemesis and risk of childhood cancer, both all types combined and separately. Cancer types with five or more exposed cases were stratified by age at diagnosis. All analysis were adjusted for maternal age, ethnicity and smoking, in addition to the offspring's Apgar score, placental weight and birth weight. Relative risks with 95% confidence intervals were calculated.

RESULTS

In total 14,805 cases and approximately ten controls matched on time, country of birth, sex and year of birth per case (147,709) were identified. None of the cancer types, analyzed combined or separately, revealed significant association with hyperemesis. When stratified according to age at diagnosis, we observed a RR 2.13 for lymphoma among adolescents aged 11-20 years ((95% CI 1.14-3.99), after adjustment for maternal ethnicity and maternal age, RR 2.08 (95% CI 1.11-3.90)). The finding was not apparent when a stricter level of statistical significance was applied.

CONCLUSIONS

The main finding of this paper is that hyperemesis does not seem to increase cancer risk in offspring. The positive association to lymphoma may be by chance and needs confirmation.

Genetic and nongenetic risk factors for childhood cancer

The causes of childhood cancer have been systematically studied for decades, but apart from high-dose radiation and prior chemotherapy there are few strong external risk factors. However, inherent risk factors including birth weight, parental age, and congenital anomalies are consistently associated with most types of pediatric cancer. Recently the contribution of common genetic variation to etiology has come into focus through genome-wide association studies. These have highlighted genes not previously implicated in childhood cancers and have suggested that common variation explains a larger proportion of childhood cancers than adult. Rare variation and nonmendelian inheritance may also contribute to childhood cancer risk but have not been widely examined.

Maternal and perinatal risk factors for childhood cancer: record linkage study

OBJECTIVE

To investigate maternal and perinatal risk factors for childhood cancer.

STUDY DESIGN

Case-control analysis of linked records from the Aberdeen Maternity and Neonatal Databank with the Scottish Cancer Registry and the General Registry of Births and Deaths in Scotland was carried out.

SETTING

Aberdeen, Scotland.

PARTICIPANTS

Cases (n=176) comprised children diagnosed with cancer under 15 years or recorded as having died of cancer. Four controls per case were matched by age and gender.

RISK FACTORS TESTED

Maternal age, body mass index, social class, marital status and smoking as well as pre-eclampsia, antepartum haemorrhage and previous miscarriage, gestational age, birth weight and Apgar scores were compared between groups to test for association with cancer. ORs with 95% CIs were calculated using conditional logistic regression in univariable and multivariable models.

RESULTS

Of the maternal characteristics tested, mother's age at delivery (cases mean 28.9 (SD 5.6) years vs controls mean 30.2 (SD 4.6), p=0.002) and smoking status (38.6% smokers among cases, 29.7% among controls, p=0.034) were found to be different between groups. Of the perinatal factors tested, low Apgar score at 5 min (adjusted OR (AOR) 4.59, 95% CI 1.52 to 13.87) and delivery by caesarean section (AOR 1.95, 95% CI 1.30 to 2.92) showed statistically significant associations with childhood cancer in the multivariable model.

CONCLUSIONS

Younger maternal age, maternal smoking, delivery by caesarean section and low Apgar score at 5 min were independently associated with increased risk of childhood cancer. These general findings should be interpreted with caution as this study did not have the power to detect any association with individual diagnostic categories of childhood cancer.

Birth characteristics and risk of lymphoma in young children

BACKGROUND

Lymphoma is the third most common childhood malignancy and comprises two types, Hodgkin lymphoma (HL) and non-Hodgkin lymphoma (NHL). The etiology of pediatric lymphomas is largely unknown, but has been suggested to have prenatal origins.

METHODS

In this population-based study, California birth certificates were identified for 478 lymphoma cases diagnosed in children 0-5 years of age between 1988 and 2007; 208,015 controls frequency-matched by birth year were randomly selected from California birth records.

RESULTS

Compared to non-Hispanic whites, Hispanic children had an increased risk of HL (odds ratio (OR) and 95% confidence interval (CI) 2.43 [1.14, 5.17]), and in particular, were diagnosed more often with the mixed cellularity subtype. For all types of lymphoma, we observed an about twofold risk increase with indicators for high risk pregnancies including tocolysis, fetopelvic disproportion and previous preterm birth. NHL risk doubled with the complication premature rupture of membranes (OR and 95% CI 2.18 [1.12, 4.25]) and HL with meconium staining of amniotic fluids (OR and 95% CI 2.55 [1.01, 6.43]).

CONCLUSION

These data support previously reported associations between Hispanic ethnicity and HL and suggest that pregnancy related factors, such as intra-uterine infections and factors associated with preterm labor, may be involved in lymphoma pathogenesis.

Case-control study of paternal occupation and social class with risk of childhood central nervous system tumours in Great Britain, 1962-2006

BACKGROUND

Paternal occupational exposures have been proposed as a risk factor for childhood central nervous system (CNS) tumours. This study investigates possible associations between paternal occupational exposure and childhood CNS tumours in Great Britain.

METHODS

The National Registry of Childhood Tumours provided all cases of childhood CNS tumours born and diagnosed in Great Britain from 1962 to 2006. Controls without cancer were matched on sex, period of birth and birth registration sub-district. Fathers' occupations were assigned to one or more of 33 exposure groups. A measure of social class was also derived from father's occupation at the time of the child's birth.

RESULTS

Of 11 119 cases of CNS tumours, 5 722 (51%) were astrocytomas or other gliomas, 2 286 (21%) were embryonal and 985 (9%) were ependymomas. There was an increased risk for CNS tumours overall with exposure to animals, odds ratio (OR) 1.40 (95% confidence intervals (CIs) 1.01, 1.94) and, after adjustment for occupational social class (OSC), with exposure to lead, OR 1.18 (1.01, 1.39). Exposure to metal-working oil mists was associated with reduced risk of CNS tumours, both before and after adjustment for OSC, OR 0.87 (0.75, 0.99).Risk of ependymomas was raised for exposure to solvents, OR 1.73 (1.02,2.92). For astrocytomas and other gliomas, risk was raised with high social contact, although this was only statistically significant before adjustment for OSC, OR 1.15 (1.01,1.31). Exposure to paints and metals appeared to reduce the risk of astrocytomas and embryonal tumours, respectively. However, as these results were the result of a number of statistical tests, it is possible they were generated by chance.Higher social class was a risk factor for all CNS tumours, OR 0.97 (0.95, 0.99). This was driven by increased risk for higher social classes within the major subtype astrocytoma, OR 0.95 (0.91, 0.98).

CONCLUSION

Our results provide little evidence that paternal occupation is a significant risk factor for childhood CNS tumours, either overall or for specific subtypes. However, these analyses suggest that OSC of the father may be associated with risk of some childhood CNS cancers.

Epidemiology of childhood acute myeloid leukemia

Although leukemia is the most common childhood cancer diagnosis, the subtype, acute myeloid leukemia (AML), is less common and fewer etiologic studies exist. This review summarizes the major risk factors for AML. We searched the literature using PubMed for articles on childhood AML and reviewed 180 articles. While few risk factors are definitive, we identified several with consistent evidence of a possible effect. Thorough analysis of genetic and epigenetic factors is missing from this literature and methodological issues are unresolved. Future studies should more closely examine causal mechanisms, improve exposure measurement, and include analysis using genetic and epigenetic factors.

Hospitalisation for infection prior to diagnosis of acute lymphoblastic leukaemia in children

BACKGROUND

It has been proposed that infections in infancy and early childhood are associated with a reduced risk of childhood acute lymphoblastic leukaemia (ALL). We tested this hypothesis in a register-based study of hospitalisations for infectious diseases prior to diagnosis of childhood ALL.

PROCEDURE

A nation-wide cohort encompassing all Danish children aged 0-14 years and born between 1977 and 2008 (N = 1,778,129) was established and followed for hospitalisations for infectious diseases and risk of childhood ALL. The exposure was lagged 1 year to limit reverse causality. In the statistical analyses exposure was defined as (time dependent) number of early or late (before 2 or at/after 2 years of age) hospitalisations to further explore possible age-dependent associations.

RESULTS

A total of 815 children were diagnosed with ALL during follow-up. Risk of ALL was associated neither with hospitalisations for infectious diseases before (incidence rate ratio = 0.92, 95% confidence interval 0.78-1.07) nor at/after 2 years of age (incidence rate ratio = 1.04, 95% confidence interval 0.81-1.32). This also applied to subsets of ALL supposedly initiated prenatally.

CONCLUSION

The absence of association between hospitalisation for infections and risk of childhood ALL directs future investigations of the role of infections in development of childhood ALL towards exploration of less severe infections.

Hyperemesis gravidarum in the Medical Birth Registry of Norway - a validity study

Background

Valid registration of medical information is essential for the quality of registry-based research. Hyperemesis gravidarum (HG) is characterized by severe nausea and vomiting, weight loss and electrolyte imbalance starting before 22nd gestational week. Given the fact that HG is a generally understudied disease which might have short- and long- term health consequences for mother and child, it is of importance to know whether potential misclassification bias influences the results of future studies. We therefore assessed the validity of the HG-registration in the in Medical Birth Registry of Norway (MBRN) using hospital records.

Methods

The sample comprised all women registered in MBRN with HG and who delivered at Ullevål and Akershus hospitals in 1.1.-31.3.1970, 1.4.-30.6.1986, 1.7.-30.9.1997 and 1.10.-31.12.2001. A random sample of 10 women per HG case, without HG according to MBRN, but who delivered during the same time periods at the same hospitals was also collected. The final sample included 551 women. Sensitivity, specificity, positive and negative predictive values (PPV and NPV) were estimated using strict and less strict diagnostic criteria of HG, indicating severe and mild HG, respectively. Hospital journals were used as gold standard.

Results

Using less strict diagnostic criteria of HG, sensitivity, specificity, PPV and NPV were 83.9% (95% CI: 67.4-92.9), 96.0% (95% CI: 93.9-97.3), 55.3% (95% CI: 41.2-68.6) and 99.0% (95% CI: 97.7-99.6), respectively. For strict diagnostic criteria, being hospitalised due to HG the corresponding values were 64% (95% CI: 38.8-87.2), 92% (95% CI: 90.2-94.6), 18.6% (95% CI: 10.2-31.9) and 99.0% (95% CI: 97.7-99.6).

Conclusions

The results from our study are comparable to previous research on disease registration in MBRN, and show that MBRN can be considered valid for mild HG but not for severe HG.

Case-control study of paternal occupation and childhood leukaemia in Great Britain, 1962-2006

Background:

Paternal occupational exposures have been proposed as a risk factor for childhood leukaemia. This study investigates possible associations between paternal occupational exposure and childhood leukaemia in Great Britain.

Methods:

The National Registry of Childhood Tumours provided all cases of childhood leukaemia born and diagnosed in Great Britain between 1962 and 2006. Controls were matched on sex, period of birth and birth registration subdistrict. Fathers’ occupations were assigned to 1 or more of 33 exposure groups. Social class was derived from father’s occupation at the time of the child’s birth.

Results:

A total of 16 764 cases of childhood leukaemia were ascertained. One exposure group, paternal social contact, was associated with total childhood leukaemia (odds ratio 1.14, 1.05–1.23); this association remained significant when adjusted for social class. The subtypes lymphoid leukaemia (LL) and acute myeloid leukaemia showed increased risk with paternal exposure to social contact before adjustment for social class. Risk of other leukaemias was significantly increased by exposure to electromagnetic fields, persisting after adjustment for social class. For total leukaemia, the risks for exposure to lead and exhaust fumes were significantly <1. Occupationally derived social class was associated with risk of LL, with the risk being increased in the higher social classes.

Conclusion:

Our results showed some support for a positive association between childhood leukaemia risk and paternal occupation involving social contact. Additionally, LL risk increased with higher paternal occupational social class.

Infectious illness in children subsequently diagnosed with acute lymphoblastic leukemia: modeling the trends from birth to diagnosis

Although there is increasing evidence that immune dysregulation in children who develop acute lymphoblastic leukemia (ALL) is detectable from birth, debate about the role of infectious exposures in infancy continues. With the aim of quantifying children's infectious exposures, investigators have used a number of infection exposure proxies, but there is a lack of consistency in findings, with some markers indicating increased ALL risks and others decreased risks, the disparity being evident both within and between studies. Accordingly, the authors conducted an in-depth analysis of key infection exposure proxies used in the United Kingdom Childhood Cancer Study, a national population-based case-control study conducted over the period 1991-1996, which combined data from medical records, parental interview, and population census. This longitudinal approach revealed the marked deterioration in immune response that emerged around 5 months prior to ALL diagnosis and confirmed that infectious diagnoses in the first year of life were significantly increased (P < 0.05) in children who developed leukemia between 2 and 14 years of age, as well as in those who had birth orders >1, were not breastfed, lived in deprived areas, or were diagnosed with eczema. By contrast, no association between infectious illness and preschool activity was detected, the lower infection levels among controls whose mothers reported attendance contributing to a significantly reduced ALL odds ratio.

Birth weight and other perinatal characteristics and childhood leukemia in California

AIMS

We conducted a large registry-based study in California to investigate the association of perinatal factors and childhood leukemia with analysis of two major subtypes, acute lymphocytic leukemia (ALL) and acute myeloid leukemia (AML).

METHODS

We linked California cancer and birth registries to obtain information on 5788 cases and 5788 controls matched on age and sex (1:1). We examined the association of birth weight, gestational age, birth and pregnancy order, parental ages, and specific conditions during pregnancy and risk of total leukemia, ALL and AML using conditional logistic regression, with adjustment for potential confounders.

RESULTS

The odds ratio (OR) per 1000 g increase in birth weight was 1.11 for both total leukemia and ALL. The OR were highest for babies weighing ≥ 4500 g with reference < 2500 g: 1.59 (95% CI: 1.05-2.40) and 1.70 (95% CI: 1.08-2.68) for total leukemia and ALL, respectively. For AML, increase in risk was also observed but the estimate was imprecise due to small numbers. Compared to average-for-gestational age (AGA), large-for-gestational age (LGA) babies were at slightly increased risk of total childhood leukemia (OR = 1.10) and both ALL and AML (OR = 1.07 and OR = 1.13, respectively) but estimates were imprecise. Being small-for-gestational age (SGA) was associated with reduced risk of childhood leukemia (OR = 0.81, 95% CI: 0.67-0.97) and ALL (OR = 0.77, 95% CI: 0.63-0.94), but not AML. Being first-born was associated with decreased risk of AML only (OR = 0.70; 95% CI: 0.53-0.93). Compared to children with paternal age <25 years, children with paternal age between 35 and 45 years were at increased risk of total childhood leukemia (OR = 1.12; 95% CI: 1.04-1.40) and ALL (OR = 1.23; 95% CI: 1.04-1.47). None of conditions during pregnancy examined or maternal age were associated with increased risk of childhood leukemia or its subtypes.

CONCLUSIONS

Our results suggest that high birth weight and LGA were associated with increased risk and SGA with decreased risk of total childhood leukemia and ALL, being first-born was associated with decreased risk of AML, and advanced paternal age was associated with increased risk of ALL. These findings suggest that associations of childhood leukemia and perinatal factors depend highly on subtype of leukemia.

Parental age, family size, and offspring's risk of childhood and adult acute leukemia

BACKGROUND

An association between childhood acute leukemia and advanced parental age was observed more than 50 years ago, and the association has been repeated in several, but not all, subsequent studies. In contrast to the many studies addressing childhood leukemia, few have included adult patients.

METHODS

In this register-based case-control study, we examined the association between parental age and incidence of acute leukemia in 2,660 childhood cases and 4,412 adult cases of acute leukemia, compared with 28,288 age-matched controls selected from a population-based register. Relative risks were estimated with conditional logistic regression.

RESULTS

We found a small increased risk of childhood acute lymphoblastic leukemia with increasing paternal age (adjusted OR, 1.05 per 5-year increase in age). Risk estimates were similar for childhood acute myeloid leukemia (AML), whereas no association was found with adult leukemia. Meanwhile, we observed a decreased risk of adult AML with increasing number of siblings, both older and younger.

CONCLUSIONS

The results support the idea of a prenatal etiology of leukemia but indicate that parental age effects are limited to childhood cases.

IMPACT

This is the first large study on parental age and leukemia risk, which includes adult cases. The finding on family size and risk of adult AML needs to be validated in future studies.

Is birth weight associated with childhood lymphoma? A meta-analysis

Several risk factors have been identified for childhood lymphomas. The purpose of this meta-analysis was to synthesize current evidence regarding the association between birth weight with primarily the risk for non-Hodgkin lymphoma (NHL), given its similarity to acute lymphoblastic leukemia, Hodgkin lymphoma (HL) and any category of lymphoma. Two cohort (278,751 children) and seven case-control studies (2,660 cases and 69,274 controls) were included. Effects estimates regarding NHL, HL and any lymphoma were appropriately pooled using fixed or random effects model in two separate analyses: specifically, high was compared to normal or any birth weight. Similarly, low was compared to normal or any birth weight. No statistically significant association was found between high birth weight, as compared to normal birth weight, and risk for NHL plus Burkitt lymphoma (OR = 1.17, 95% CI = 0.76-1.80, random effects), HL (OR = 0.94, 95% CI = 0.64-1.38, fixed effects) or any plus Burkitt lymphoma (OR = 1.09, 95% CI = 0.76-1.56, fixed effects). A null association emerged when low was compared with normal birth weight for NHL plus Burkitt lymphoma (OR = 1.07, 95% CI = 0.71-1.62, random effects), HL (OR = 0.94, 95% CI = 0.54-1.65, fixed effects) or any plus Burkitt lymphoma (OR = 1.02, 95% CI = 0.79-1.33, fixed effects). Accordingly, no association was found when high or low birth weight was compared to any birth weight. Although current evidence suggests no association, birth weight might be a too crude indicator to reveal a genuine association of fetal growth with specific lymphoma categories; hence, there is an emerging need for use of more elaborate proxies, at least those accounting for gestational week.

Childhood Hodgkin's lymphoma, non-Hodgkin's lymphoma and factors related to the immune system: the Escale Study (SFCE)

The study investigated the role of factors considered related to the early stimulation of the immune system in the aetiology of childhood lymphoma. The national registry-based case-control study, Escale, was carried out in France over the period 2003-2004. Population controls were frequency matched with the cases on age and gender. Data were obtained from structured telephone questionnaires administered to mothers. Odds ratios (ORs) were estimated using unconditional regression models adjusted for potential confounders. Data from 128 cases of Hodgkin's lymphoma (HL) aged 5-14 years, 164 cases of non-Hodgkin's lymphoma (NHL) aged 2-14 years and 1,312 controls were analyzed. Negative associations were observed between HL and day care attendance [OR = 0.5 (0.2-1.2)] and between HL and repeated early common infections among non-breastfed children [OR = 0.3 (.2-0.7), p = 0.003] [OR for breastfed children: 1.0 (.5-2.1)], but not for the other factors investigated. Negative associations were observed between NHL and birth order 3 or more [OR = 0.7 (0.4-1.1)], prolonged breastfeeding [OR = 0.5 (0.3-1.0)], regular contact with farm animals [OR = 0.5 (0.3-1.0)], frequent farm visits in early life [OR = 0.6 (0.4-1.1)] and history of asthma [OR = 0.6 (0.3-1.1)]. In conclusion, the results partly support the hypothesis that an abnormal maturation of the immune system may play a role in childhood HL or NHL, and call for further investigations.

Early life exposure to diagnostic radiation and ultrasound scans and risk of childhood cancer: case-control study

OBJECTIVE

To examine childhood cancer risks associated with exposure to diagnostic radiation and ultrasound scans in utero and in early infancy (age 0-100 days).

DESIGN

Case-control study.

SETTING

England and Wales.

PARTICIPANTS

2690 childhood cancer cases and 4858 age, sex, and region matched controls from the United Kingdom Childhood Cancer Study (UKCCS), born 1976-96.

MAIN OUTCOME MEASURES

Risk of all childhood cancer, leukaemia, lymphoma, and central nervous system tumours, measured by odds ratios.

RESULTS

Logistic regression models conditioned on matching factors, with adjustment for maternal age and child's birth weight, showed no evidence of increased risk of childhood cancer with in utero exposure to ultrasound scans. Some indication existed of a slight increase in risk after in utero exposure to x rays for all cancers (odds ratio 1.l4, 95% confidence interval 0.90 to 1.45) and leukaemia (1.36, 0.91 to 2.02), but this was not statistically significant. Exposure to diagnostic x rays in early infancy (0-100 days) was associated with small, non-significant excess risks for all cancers and leukaemia, as well as increased risk of lymphoma (odds ratio 5.14, 1.27 to 20.78) on the basis of small numbers.

CONCLUSIONS

Although the results for lymphoma need to be replicated, all of the findings indicate possible risks of cancer from radiation at doses lower than those associated with commonly used procedures such as computed tomography scans, suggesting the need for cautious use of diagnostic radiation imaging procedures to the abdomen/pelvis of the mother during pregnancy and in children at very young ages.

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.

Birth order and risk of childhood cancer: a pooled analysis from five US States

The causes of childhood cancers are largely unknown. Birth order has been used as a proxy for prenatal and postnatal exposures, such as frequency of infections and in utero hormone exposures. We investigated the association between birth order and childhood cancers in a pooled case-control dataset. The subjects were drawn from population-based registries of cancers and births in California, Minnesota, New York, Texas and Washington. We included 17,672 cases <15 years of age who were diagnosed from 1980 to 2004 and 57,966 randomly selected controls born 1970-2004, excluding children with Down syndrome. We calculated odds ratios and 95% confidence intervals using logistic regression, adjusted for sex, birth year, maternal race, maternal age, multiple birth, gestational age and birth weight. Overall, we found an inverse relationship between childhood cancer risk and birth order. For children in the fourth or higher birth order category compared to first-born children, the adjusted OR was 0.87 (95% CI: 0.81, 0.93) for all cancers combined. When we examined risks by cancer type, a decreasing risk with increasing birth order was seen in the central nervous system tumors, neuroblastoma, bilateral retinoblastoma, Wilms tumor and rhabdomyosarcoma. We observed increased risks with increasing birth order for acute myeloid leukemia but a slight decrease in risk for acute lymphoid leukemia. These risk estimates were based on a very large sample size, which allowed us to examine rare cancer types with greater statistical power than in most previous studies, however the biologic mechanisms remain to be elucidated.

Cancer risk in children and young adults conceived by in vitro fertilization

OBJECTIVES

Studies conducted so far have found no statistically significant increased risk for cancer among children who are born after in vitro fertilization (IVF).

METHODS

We followed 26,692 children who were born after IVF during the years 1982-2005 by using the Swedish Cancer Register and compared the number of children who had cancer and were born after IVF with children who were not conceived by IVF. Adjustment was made for year of birth.

RESULTS

Maternal age, parity, smoking, subfertility, previous miscarriages, BMI, and multiple births did not significantly affect cancer risk in offspring. High birth weight, premature delivery, and the presence of respiratory diagnoses and low Apgar score were risk factors for cancer. We identified 53 cases of cancer in children who were born after IVF against 38 expected cases: 18 of them with hematologic cancer (15 of them acute lymphoblastic leukemia), 17 with eye or central nervous system tumors, and 12 with other solid cancers. There were 6 cases of Langerhans histiocytosis against 1.0 expected. The total cancer risk estimate was 1.42 (95% confidence interval: 1.09-1.87).

CONCLUSIONS

We found a moderately increased risk for cancer in children who were conceived by IVF. Putative intermediary factors could be preterm birth and neonatal asphyxia.

Aetiology of childhood leukaemia

The acute leukaemias account for about 30% of all malignancy seen in childhood across the Western world. A peak incidence of precursor B cell ALL has emerged as socio-economic conditions have improved in countries worldwide. From twin studies and the use of neonatal blood spots it has been possible to back track the first initiating genetic events within critical haemopoietic cells to foetal development in utero for most precursor B cell ALL and some cases of AML. These events may occur as part of normal foetal development. Whether other factors (environmental or constitutional) are involved to increase the chance of these first genetic changes happening is unclear. For some leukaemias (e.g. infant MLL positive ALL) the first event appears adequate to create a malignant clone but for the majority of ALL and AML further 'genetic' changes are required, probably postnatal. Many environmental factors have been proposed as causative for leukaemia but only ionising irradiation and certain chemicals, e.g. benzene and cytotoxics (alkylators and topoisomerase II inhibitors) have been confirmed and then principally for acute myeloid leukaemia. It appears increasingly likely that delayed, dysregulated responses to 'common' infectious agents play a major part in the conversion of pre-leukaemic clones into overt precursor B cell ALL, the most common form of childhood leukaemia. Constitutional polymorphic alleleic variants in immune response genes (especially the HLA Class II proteins) and cytokines may play a role in determining the type of immune response. High penetrance germ-line mutations are involved in only about 5% of childhood leukaemias (more in AML than ALL). There is little evidence to support any role of viral transformation in causation, unlike in animals. Other environmental factors for which some evidence exists include non-ionising electromagnetic radiation and electric fields, although their mode of action in leukaemogenesis remains unclear. There is no single cause for childhood leukaemia and for most individuals a combination of factors appears to be necessary; all involving gene-environment interactions. To date few clear preventative measures have emerged, except the complete avoidance of first trimester X-rays in pregnancy; a healthy diet with adequate oral folic acid intake both preconception and early in pregnancy; and the early exposure of children to other children outside the home to facilitate stimulation and maturation of the natural immune system. Here then are clear echoes of the "hygiene hypothesis" regarding the initiation of allergies, autoimmune disease and type I diabetes mellitus in children and young people.

Birth weight, sex and childhood cancer: A report from the United Kingdom Childhood Cancer Study

Birth weight has been linked to the risk of developing childhood cancer, in particular childhood leukaemia. However, despite many childhood cancers having a male predominance and boys generally weighing more than girls at birth few studies have reported sex-specific associations. The relationship between birth weight and childhood cancer risk was examined using information from a national case-control study. Children (0-14 years) newly diagnosed with cancer in GB were ascertained between 1991 and 1996 (n=3651) and for comparison, controls matched on sex, month and year of birth were identified from primary care population registers (n=6337). Birth weights were obtained from the Office of National Statistics for all targeted subjects born in England and Wales. Overall, cases were, on average, 30 g heavier at birth than controls (p=0.003) with differences seen by cancer type; those diagnosed with hepatic tumours weighing around 500 g less than controls at birth (p<0.0001) and those with leukaemia being, on average, 50 g heavier than those without (p=0.001). An interaction between birth weight and sex was found for acute leukaemia (chi(2)=11.2, p=0.04) and when data were stratified by sex, an association between high birth weight and risk of ALL was seen with girls (>4000 g, OR 1.86, 95% CI 1.38-2.50, chi(2) for trend 20.2, p<0.0001). Our results support the hypothesis that birth weight is an important determinant for childhood cancer. In addition, the data are consistent with the notion that childhood leukaemia has a prenatal origin.

Molar pregnancy, childhood cancer and genomic imprinting – is there a link?

The United Kingdom Childhood Cancer Study (UKCCS) is a national multi-centre case-control study that was designed to evaluate the potential aetiological role of prenatal events in childhood cancer. The obstetric records of 2692 mothers of children diagnosed with cancer and 4864 mothers of children without cancer were available for analysis. Overall, 1754 (65%) case mothers and 3220 (66%) control mothers had at least one prior pregnancy before the birth of the index child. Of these, 12 (0.68%) of the former and 9 (0.28%) of the latter had a prior molar pregnancy (odds ratio 2.5, 95% confidence interval 1.1 - 6.1). Both childhood cancer and molar pregnancy are rare neoplastic events, and the numbers are small. Nonetheless, whilst the associations were strongest for common precursor B-cell acute lymphoblastic leukaemia (OR 5.2, 95% CI 1.9 - 14.7) and sarcoma (OR 6.2, 95% CI 1.3 - 30.3), the spread across the remaining diagnostic groups suggests that the relationship, if confirmed, may be of a generalized, rather than specific, type. This is the first time that an association between childhood cancer and hydatidiform mole has been reported. The UKCCS's systematic use of clinical records permitted a more precise characterization of reproductive events than is possible in investigations that rely on individuals own accounts, and we are confident that our findings cannot be explained by recall bias or other methodological limitations. Accordingly, we suggest that there may be an aetiologic connection between molar pregnancy and childhood cancer, and speculate here on the various genetic/epigenetic mechanisms that could be involved.

Environmental factors and childhood acute leukemias and lymphomas

This review considers recent studies regarding the role of environmental factors in the etiology of childhood leukemia and lymphoma. Potential environmental risk factors identified for childhood leukemia include exposure to magnetic fields of more than 0.4 micro Tessla, exposure to pesticides, solvents, benzene and other hydrocarbons, maternal alcohol consumption (but only for certain genotypes), contaminated drinking water, infections, and high birth weight. The finding of space-time clustering and seasonal variation also supports a role for infections. There is little evidence linking childhood leukemia with lifetime exposure to ionizing radiation although fetal exposures to X-rays are associated with increased risk. Breast-feeding, consumption of fresh fruit and vegetables and having allergies all appear to be protective. Burkitt lymphoma (BL) is confined to areas of the world where malaria is endemic, with the additional involvement of the Epstein-Barr virus (EBV) as a co-factor. Environmental risk factors suggested for other types of non-Hodgkin lymphoma (NHL) include exposure to ionizing radiation (both lifetime and antenatal), pesticides, and, in utero exposure to cigarette smoke, benzene and nitrogen dioxide (via the mother). Hodgkin lymphoma (HL) is especially associated with higher levels of socioeconomic deprivation, but breast-feeding seems to confer lower risk. This is consistent with an infection or immune-response mediated etiology for HL.