Leukemia is the most frequent malignant disease affecting children. To date, the etiology of childhood leukemia remains largely unknown. Few risk factors (genetic susceptibility, infections, ionizing radiation, etc.) have been clearly identified, but they appear to explain only a small proportion of cases. Considerably more uncertain is the role of other environmental risk factors, such as indoor and outdoor air pollution. We sought to summarize and quantify the association between traffic-related air pollution and risk of childhood leukemia, and further examined results according to method of exposure assessment, study quality, leukemia subtype, time period, and continent where studies took place. After a literature search yielded 6 ecologic and 20 case-control studies, we scored the studies based on the Newcastle-Ottawa Scale. The studies assessed residential exposure to pollutants from motorized traffic by computing traffic density in the neighboring roads or vicinity to petrol stations, or by using measured or modeled nitrogen dioxide and benzene outdoor air levels. Because heterogeneity across studies was observed, random-effects summary odds ratios (OR) and 95% confidence intervals (CI) were reported. Whenever possible we additionally conducted stratified analyses comparing acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML). Limiting the analysis to high-quality studies (Newcastle-Ottawa Scale ≥ 7), those using traffic density as the exposure assessment metric showed an increase in childhood leukemia risk in the highest exposure category (OR = 1.07, 95% CI 0.93-1.24). However, we observed evidence of publication bias. Results for NO2 exposure and benzene showed an OR of 1.21 (95% CI 0.97-1.52) and 1.64 (95% CI 0.91-2.95) respectively. When stratifying by leukemia type, the results based upon NO2 were 1.21 (95% CI 1.04-1.41) for ALL and 1.06 (95% CI 0.51-2.21) for AML; based upon benzene were 1.09 (95% CI 0.67-1.77) for ALL and 2.28 (95% CI 1.09-4.75) for AML. Estimates were generally higher for exposures in the postnatal period compared to the prenatal period, and for European studies compared to North American studies. Overall, our results support a link between ambient exposure to traffic pollution and childhood leukemia risk, particularly due to benzene.

Scientific opinion on the relationship between selenium and the risk of cancer has undergone radical change over the years, with selenium first viewed as a possible carcinogen in the 1940s then as a possible cancer preventive agent in the 1960s-2000s. More recently, randomized controlled trials have found no effect on cancer risk but suggest possible low-dose dermatologic and endocrine toxicity, and animal studies indicate both carcinogenic and cancer-preventive effects. A growing body of evidence from human and laboratory studies indicates dramatically different biological effects of the various inorganic and organic chemical forms of selenium, which may explain apparent inconsistencies across studies. These chemical form-specific effects also have important implications for exposure and health risk assessment. Overall, available epidemiologic evidence suggests no cancer preventive effect of increased selenium intake in healthy individuals and possible increased risk of other diseases and disorders.

Background

Exposure to pesticides has been suggested as a risk factor for childhood leukemia, but definitive evidence on this relation and the specific pesticides involved is still not clear.

Objective

We carried out a population-based case-control study in a Northern Italy community to assess the possible relation between passive exposure to agricultural pesticides and risk of acute childhood leukemia.

Methods

We assessed passive pesticide exposure of 111 childhood leukemia cases and 444 matched controls by determining density and type of agricultural land use within a 100-m radius buffer around children's homes. We focused on four common crop types, arable, orchard, vineyard and vegetable, characterized by the use of specific pesticides that are potentially involved in childhood induced leukemia. The use of these pesticides was validated within the present study. We computed the odds ratios (OR) of the disease and their 95% confidence intervals (CI) according to type and density of crops around the children's homes, also taking into account traffic pollution and high-voltage power line magnetic field exposure.

Results

Childhood leukemia risk did not increase in relation with any of the crop types with the exception of arable crops, characterized by the use of 2.4-D, MCPA, glyphosate, dicamba, triazine and cypermethrin. The very few children (n=11) residing close to arable crops had an OR for childhood leukemia of 2.04 (95% CI 0.50-8.35), and such excess risk was further enhanced among children aged <5 years.

Conclusions

Despite the null association with most crop types and the statistical imprecision of the estimates, the increased leukemia risk among children residing close to arable crops indicates the need to further investigate the involvement in disease etiology of passive exposure to herbicides and pyrethroids, though such exposure is unlikely to play a role in the vast majority of cases.

Background. Some observational studies have suggested that excess dietary intake of polyunsaturated fatty acids such as linoleic acid increases cutaneous melanoma risk. We aimed at examining the association between serum fatty acids and melanoma risk by conducting a population-based case-control study in a northern Italy community. Methods. The percentage composition of 12 fatty acids was determined in 51 newly diagnosed melanoma patients and 51 age- and sex-matched population controls by extracting total lipids from serum samples using thin layer and gas chromatography. Conditional logistic regression was used to estimate the relative risk of melanoma associated with tertiles of percentage composition of each fatty acid as well as groupings including saturated, monounsaturated, and polyunsaturated fatty acids. Results. We found a slightly increased melanoma risk for stearic and arachidic acids proportion, with and without adjustment for potential confounders. For an n-3 polyunsaturated fatty acid, docosapentaenoic acid, we found a male-specific direct association with melanoma risk. No other associations emerged for the other saturated, monounsaturated, and polyunsaturated fatty acids, individually or grouped by type. Conclusions. These findings do not suggest a major role of fatty acids, including linoleic acid, on risk of cutaneous melanoma, though their evaluation is limited by the small sample size.

A few studies have suggested an association between maternal exposure to ambient air pollution from vehicular traffic and risk of congenital anomalies in the offspring, but epidemiologic evidence is neither strong nor entirely consistent. In a population-based case-control study in a Northern Italy community encompassing 228 cases of birth defects and 228 referent newborns, we investigated if maternal exposure to PM10 and benzene from vehicular traffic during early pregnancy, as estimated through a dispersion model, was associated with excess teratogenic risk. In conditional logistic regression analysis, and with adjustment for the other pollutant, we found that higher exposure to PM10 but not benzene was associated with increased risk of birth defects overall. Anomaly categories showing the strongest dose-response relation with PM10 exposure were musculoskeletal and chromosomal abnormalities but not cardiovascular defects, with Down syndrome being among the specific abnormalities showing the strongest association, though risk estimates particularly for the less frequent defects were statistically very unstable. Further adjustment in the regression model for potential confounders did not considerably alter the results. All the associations were stronger for average levels of PM10 than for their maximal level. Findings of this study give some support for an excess teratogenic risk following maternal exposure during pregnancy to PM10, but not benzene. Such association appears to be limited to some birth defect categories.

Benzene, a recognized occupational leukemogen in adults, has been hypothesized to also increase the risk of childhood leukemia. We carried out a population-based case-control study in a northern Italy community involving 83 cases with acute childhood leukemia diagnosed in the years 1998-2009 and 332 matched controls. We assessed residential exposure to benzene and to particulate matter ≤10 μm (PM10) from motorized traffic using geocoded residences and detailed emission and dispersion modeling. Exposure to benzene, and to a lesser extent to PM10, appeared to be independently associated with an excess leukemia risk. When we stratified the study population by age and by leukemia subtype, the relative risk associated with benzene exposure was higher among children aged less than 5 years, and despite small numbers this relation appeared to be considerably stronger for acute myeloid leukemia than for acute lymphoblastic leukemia. Overall, these findings suggest that exposure to low levels of benzene released from motorized traffic may increase the risk of childhood leukemia, and suggest a possible independent effect of PM10, although unmeasured confounding due to other pollutants cannot be ruled out.

Background

Some results from laboratory and epidemiologic studies suggest that diet may influence the risk of melanoma, but convincing evidence for a role of single nutrients or food items is lacking. Diet quality, which considers the combined effect of multiple food items, may be superior for examining this relation.

Objective

We sought to assess whether diet quality, evaluated with the use of 4 different dietary indexes, is associated with melanoma risk.

Methods

In this population-based case-control study, we analyzed the relation between 4 diet quality indexes, the Healthy Eating Index 2010 (HEI-2010), Dietary Approaches to Stop Hypertension (DASH) index, Greek Mediterranean Index (GMI), and Italian Mediterranean Index (IMI), and melanoma risk in a northern Italian community, with the use of data from 380 cases and 719 matched controls who completed a semiquantitative food frequency questionnaire.

Results

In the overall sample, we found an inverse association between disease risk and the HEI-2010 and DASH index, but not the Mediterranean indexes, adjusting for potential confounders (skin phototype, body mass index, energy intake, sunburn history, skin sun reaction, and education). However, in sex stratified analyses, the association appeared only in women (P-trend: 0.10 and 0.04 for the HEI-2010 and DASH index, respectively). The inverse relations were stronger in women younger than age 50 y than in older women, for whom the GMI and IMI scores also showed an inverse association with disease risk (P-trend: 0.05 and 0.02, respectively).

Conclusions

These results suggest that diet quality may play a role in cutaneous melanoma etiology among women.

Background

Although studies have consistently found an association between childhood leukaemia risk and magnetic fields, the associations between childhood leukaemia and distance to overhead power lines have been inconsistent. We pooled data from multiple studies to assess the association with distance and evaluate whether it is due to magnetic fields or other factors associated with distance from lines.

Methods

We present a pooled analysis combining individual-level data (29,049 cases and 68,231 controls) from 11 record-based studies.

Results

There was no material association between childhood leukaemia and distance to nearest overhead power line of any voltage. Among children living < 50 m from 200 + kV power lines, the adjusted odds ratio for childhood leukaemia was 1.33 (95% CI: 0.92-1.93). The odds ratio was higher among children diagnosed before age 5 years. There was no association with calculated magnetic fields. Odds ratios remained unchanged with adjustment for potential confounders.

Conclusions

In this first comprehensive pooled analysis of childhood leukaemia and distance to power lines, we found a small and imprecise risk for residences < 50 m of 200 + kV lines that was not explained by high magnetic fields. Reasons for the increased risk, found in this and many other studies, remains to be elucidated.

Although recent studies have demonstrated associations between nonchromosomal birth defects and several pediatric cancers, less is known about their role on childhood leukemia susceptibility. Using data from the Childhood Cancer and Leukemia International Consortium, we evaluated associations between nonchromosomal birth defects and childhood leukemia. Pooling consortium data from 18 questionnaire-based and three registry-based case-control studies across 13 countries, we used multivariable logistic regression models to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for the association between a spectrum of birth defects and leukemia. Our analyses included acute lymphoblastic leukemia (ALL, n = 13 115) and acute myeloid leukemia (AML, n = 2120) cases, along with 46 172 controls. We used the false discovery rate to account for multiple comparisons. In the questionnaire-based studies, the prevalence of birth defects was 5% among cases vs 4% in controls, whereas, in the registry-based studies, the prevalence was 11% among cases vs 7% in controls. In pooled adjusted analyses, there were several notable associations, including (1) digestive system defects and ALL (OR = 2.70, 95% CI: 1.46-4.98); (2) congenital anomalies of the heart and circulatory system and AML (OR = 2.86, 95% CI: 1.81-4.52) and (3) nervous system defects and AML (OR = 4.23, 95% CI: 1.50-11.89). Effect sizes were generally larger in registry-based studies. Overall, our results could point to novel genetic and environmental factors associated with birth defects that could also increase leukemia susceptibility. Additionally, differences between questionnaire- and registry-based studies point to the importance of complementary sources of birth defect phenotype data when exploring these associations.