Abstract 1217: The association between birth order and childhood brain tumors: A systematic review and meta-analysis

Abstract

Abstract Background: The incidence of childhood brain tumors (CBT) has increased worldwide, likely resulting from the improvements of early diagnostics. The only known risk factors for CBT are the Li-Fraumeni syndrome and iodization. While both genetic and environmental factors are suggested roles in CBT, birth characteristics, including birth order, maternal age, and mode of delivery, might present the interactions between genetic susceptibility and perinatal environmental causes. Birth order has been hypothesized to play an important role in CBT carcinogenesis due to its possible role as proxy for 1) early infection exposure and 2) hormone levels since first pregnancy differs endocrinologically from later pregnancies. We conducted a systematic review and meta-analysis to clarify the association between birth order and CBT. Methods: We followed established guidelines to systematically search OvidMedline, PubMed, and the Cochrane Library for English-language studies (both case-control and cohort designs) published prior to November 2017. Meta-analysis provided pooled risk estimates and their 95% confidence intervals (CI) for birth order and CBT. Funnel plots were used to identify sources of heterogeneity and publication bias. Results: We identified 16 case-control studies with a total sample of 32,439 cases and 166,144 controls. Compared to first birth order, the meta-odds ratio (mOR) for second birth order was 1.04 (95% CI 1.01-1.07), and that for third birth order was 0.98 (95% CI: 0.90-1.06). We also identified 3 cohorts comprising a total of 1,208 cases. The meta-hazard ratio (mHR) for second or higher birth order compared to first birth order was 1.00 (95% CI: 0.96-1.05). Conclusions: We found no overall association between birth order and CBT in both case-control and cohort study designs; the small association observed for second birth order in case-control studies deserves further consideration. Limited statistical power might have hampered the results of the other analyses. Citation Format: Mai V. Nguyen, Mo Thi Tran, Chi TDu Tran, Quang H. Tran, Thuy Thi-Van Tuong, Linh C. Le, Paolo Boffetta, Hung N. Luu. The association between birth order and childhood brain tumors: A systematic review and meta-analysis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1217.