Impact of Birth Cohorts in Breast Cancer Risk Among South Korean Women.

Abstract

The incidence of breast cancer among South Korean women, a historically low-risk population, has increased over the past 3 decades, with marked changes in socioeconomic environment by birth cohort. We investigated associations between breast cancer risk and reproductive factors as well as the impact of birth cohort in those associations. This was a cross-sectional study of data from the Korea National Health and Nutrition Examination Survey for 2013-2016. Data from 10 012 parous women 30 years or older were analyzed using descriptive statistics and Cox multivariate regression after adjusting for socioeconomic status, educational level, occupation, and birth cohort. Of the reproductive factors considered-age at menarche, number of pregnancies, age at first birth, age at last birth, breastfeeding duration, and use of oral contraceptives-only age at menarche was associated with breast cancer risk. Higher educational level, not having an occupation, and younger birth cohort were also associated with increased risk of breast cancer, with birth cohort the strongest of these impact factors. Whereas the relationship between reproductive factors and breast cancer risk was relatively weak, birth cohort was the most important risk factor for breast cancer. The results provide a basis and a rationale for developing birth cohort-based clinical guidelines for breast cancer prevention and early detection, treatment, and survivorship. These findings should also be useful to researchers in other countries experiencing rapid changes in breast cancer incidence.