Type 2 diabetes, obesity, and breast cancer risk among Japanese women of the atomic bomb survivor cohort. (June 2019)

• Record Type: Journal Article
• Authors: Maskarinec, Gertraud; Sadakane, Atsuko; Sugiyama, Hiromi; Brenner, Alina; Tatsukawa, Yoshimi; Grant, Eric
• Is Part Of: Cancer epidemiology. Volume 60(2019:Jun.)
• Page Start: 179
• Page End: 184
• Publication Date: 2019-06
• Subjects: Breast cancer -- Obesity -- Type 2 diabetes -- Japan -- Cohort study -- Longitudinal analysis; Cancer -- Epidemiology -- Periodicals; Cancer -- Prevention -- Periodicals; Cancer -- Diagnosis -- Periodicals; Carcinogenesis -- Periodicals; 616.994005
• DOI: 10.1016/j.canep.2019.04.009
• Languages: English
• ISSNs: 1877-7821

Abstract

Highlights: The role of obesity and diabetes in breast cancer etiology varies across geographic areas and populations of different ethnic background. The long-term cohort of Japanese atomic bomb survivors has relatively low obesity and diabetes prevalence. Among this cohort of Japanese women, excess body weight predicted higher breast cancer incidence while a history of diabetes did not. Despite a lower BMI in this Japanese population than in Western countries, women with excess weight had a higher risk of developing breast cancer. Abstract: Background: Much less is known about diabetes than obesity as a predictor of breast cancer incidence and most previous studies have been conducted in white populations. Therefore, this project within the Radiation Effects Research Foundation's cohort of Japanese atomic bomb survivors aimed to determine the independent contributions of obesity and diabetes to develop breast cancer. Methods: After excluding women with unknown A-bomb radiation dose, a radiation dose of ≥100 mGy, a pre-existing history of breast cancer, and missing body mass index (BMI), the analysis included 29, 818 women. Breast cancer status and deaths until 2009 were identified from cancer registries and vital records. Cox regression with age as the time metric was applied to estimate hazard ratios (HR) and 95% confidence intervals (CI) for BMI and diabetes status as time-varying exposures alone and in combination while adjusting for known confounders. Results: Diabetes prevalence increased from 2.6% to 5.3% and 7.5% from the first to the second and third data collection. During 27.6 ± 12.2 years of follow-up, 703 women had developed breast cancer (mean age of 66.0 ± 12.9 years) and 31 (4.4%) had been diagnosed with diabetes. A diagnosis of diabetes was not significantly associated with breast cancer incidence without (HR 1.12, 95% CI 0.77–1.64) and with BMI (HR 1.01, 95% CI 0.69–1.49) as a covariate. The respective HRs for overweight and obesity were 1.61 (95% CI 1.34–1.93) and 2.04 (95% CI 1.40–2.97). Conclusions: Among a long-time Japanese cohort, excess body weight but not a diabetes diagnosis was significantly associated with breast cancer risk.