Childhood leukemia is the most common malignant disease in children, followed by childhood CNS/brain tumors. [1, 2] Both diseases have been recognized for a long time but little is known about the etiology of childhood leukemia and primary CNS/brain tumors.
The aims of this project were to evaluate: 1) the association of several perinatal factors with childhood leukemia as well as with CNS/brain tumors; 2) the relationships between childhood leukemia and child's and parental race, Hispanic ethnicity and socio-economic status (SES) at individual and census levels; 3) factors associated with residential mobility in childhood leukemia cases.
We conducted a large registry-based study in California using California birth and cancer registries to obtain information on childhood leukemia and CNS/brain tumor cases and controls. Information on case's diagnosis, histological subtypes, age at diagnosis, sex, and diagnosis address was obtained from California cancer registry; information on perinatal factors (birth weight, gestational age, birth order, parental age at birth, maternal complications during pregnancy, abnormal condition of a newborn), socio-demographic factors (date of birth, sex, race and ethnicity of parents and child, parental education, sources of payment for delivery, birth address) were obtained from the birth registry.
We linked California cancer and birth registries to obtain information on 5788 cases of childhood leukemia and 3308 cases of CNS/brain tumors and their 5788 and 3308 controls matched on age and sex (1:1). To address at least partially the problem with misclassification we categorized birth weight, gestational age, parental age, child and parental race and Hispanic ethnicity, individual level proxies for and census-based SES in several ways. For all analyses we used conditional logistic regression, with adjustment for potential confounders.
Our results for childhood leukemia and perinatal factors indicate 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. Our results for CNS/brain tumors and perinatal factors suggest that maternal genital herpes, blood and immunological disorders during pregnancy and newborn CNS abnormalities were associated with increased risk of CNS tumors. Maternal infections during pregnancy were associated with decreased risk of CNS tumors. Factors associated with childhood leukemia and CNS tumors varied by subtype, an indicator of different etiology for different subtypes.
We noted that Black children had decreased risk (ref. - White) and Hispanic children (ref. non-Hispanic) had increased risk of total childhood leukemia and ALL. Asian race was associated with increased risk of AML. These differences in the incidence of childhood leukemia indicate that some genetic and/or environmental/cultural (e.g., diet or lifestyle) factors are involved in etiology of childhood leukemia.
We found no evidence to support the suggestion that SES, as measured by variety of proxies is a determinant of childhood leukemia and of its both subtypes. It is likely that results of many previous studies that found an association between childhood leukemia and SES were largely influenced by selection or ecological bias.
The results of this study indicate that childhood leukemia cases in California are residentially very mobile, with 58% of them moving between birth and diagnosis. The residential mobility of childhood leukemia cases notably varied by time interval between birth and diagnosis, child's race/ethnicity, maternal age at birth, census-based SES, and the source of payment for delivery; it varied less by the distance to the nearest power line. Our results suggest that even if information on the residential mobility of subjects is unavailable, it might be possible and important to look at the distribution of factors that could be associated with residential mobility.