Parental occupational exposures and risk of childhood cancer

Author(s): Omidakhsh, Negar | Advisor(s): Ritz, Beate | Abstract: Childhood cancer remains the second most common cause of death in children living in the United States and Europe. Research to date has revealed little about the etiology of these diseases, and established risk factors are limited to certain rare genetic syndromes and polymorphisms, ionizing radiation, and congenital abnormalities. Parental occupational exposures have been associated with increased risk of some childhood cancers, including leukemia and brain tumors. However, studies on maternal exposures, and those that examine the rarer cancers, are largely lacking. For the present analyses, we utilized two datasets and examined associations between (1) parental occupational social contact and risk of hematopoietic, central nervous system (CNS) and bone cancers, (2) industry types and retinoblastoma and (3) exposure to harmful environmental agents and retinoblastoma. Our first population-based case-control study utilized a linkage of four Danish data-registries, and included 4,112 cases and 411,200 age-matched controls. High occupational social contact, jobs that have regular contact with young children or the sick, was examined from (1) conception to birth and (2) birth to diagnosis. Acute lymphoblastic leukemia (ALL) and bone cancer were inversely associated with high maternal occupational social contact from conception to birth (OR: 0.82, 95% CI: 0.64-1.04) and birth to diagnosis (OR: 0.59, 95% CI: 0.39-0.91). Children of fathers with high occupational social contact from birth to diagnosis had an increased risk of bone cancers, particularly in rural areas (OR: 1.68, 95% CI: 1.07-2.64). Parental high social contact was associated with increased risk of astrocytoma, with strongest associations found in first born children (maternal contact: OR: 1.54, 95% CI: 1.02-2.32; paternal contact: OR: 1.82, 95% CI: 1.05-3.17). Our second study utilized the same Danish dataset and examined the role of occupational industry type during two biologically relevant time periods (1) 90 days preconception to conception for fathers and (2) conception to birth for mothers and risk of retinoblastoma among offspring. Parents were grouped into major industry headings created from Danish industry codes, an extended version of the International Standard Industrial Classification of All Economic Activities. We observed increased risk of all retinoblastoma among fathers in the food and drink industry (OR: 2.27, 95% CI: 1.24-4.16) and those who sell groceries (OR: 3.56, 95% CI: 1.42-8.91). Bilateral disease was associated with paternal work in supermarkets (OR: 4.03, 95% CI: 1.52-10.71) and transportation on land (OR: 4.03, 95% CI: 1.52-10.71). For maternal occupation, we estimated an increased risk of all retinoblastoma for hospital workers or clinicians (OR: 2.05, 95% CI: 1.34-3.14). In our final multicenter study on non-familial retinoblastoma, parents of 187 unilateral and 95 bilateral cases and 155 friend controls were interviewed by telephone. Exposure information was collected retroactively through a detailed occupational questionnaire which asked fathers to report every job held in the 10 years before conception, and mothers one month prior to and during the index pregnancy. We estimated elevated odds ratios for unilateral and bilateral retinoblastoma among offspring of fathers who were exposed to polycyclic aromatic hydrocarbons (PAHs) or paints in the 10 years prior to conception. However, only for exposure to paints did confidence limits exclude the null for bilateral disease (OR: 8.76, 95% CI: 1.32-58.09). Maternal prenatal exposure to at least one of the 9 agents was related to increased risk of unilateral disease in their children (OR: 5.25, 95% CI: 1.14-24.16). Our results support the notion of a role of infections for some cancer types. Studies on the risk factors for retinoblastoma are rare and our results suggest that some parental occupational exposures may cause childhood retinoblastoma.