Effects of interval between age at first pregnancy and age at diagnosis on breast cancer survival according to menopausal status: a register-based study in Korea

BACKGROUND The influence of parity and time interval between age at first pregnancy (AFP) and age at diagnosis on breast cancer survival is not established in the same way as their influence on breast cancer risk. We aimed to investigate the association of time interval or parity with prognosis in pre- and postmenopausal women in Korea. METHODS We conducted a retrospective study of 29,167 women with breast cancer through the Korean Breast Cancer Registry from 1993-2009. Information on reproductive factors, including breastfeeding, AFP, and parity were collected from a routine questionnaire. Conditional logistic regression was used to estimate the associations between menopausal status and overall mortality (OM) and breast-cancer-specific mortality (BCSM), adjusting for treatment and stage. RESULTS High parity (≥5) increased the hazard ratios (HR) of BCSM (HR = 1.33, 95% confidence interval (CI): 0.83-2.11, p < 0.001) and OM (HR = 1.20, 95% CI: 0.85-1.68.73, p < 0.001) in premenopausal and postmenopausal women (BCSM, HR: 1.62, 95% CI: 0.93-2.82, p < 0.001; OM, HR = 1.58, 95% CI: 1.14-2.21, p <0.001). A longer time interval between age at breast cancer diagnosis and AFP reduced the HRs of BCSM (HR = 0.97, 95% CI: 0.96-0.98, p = 0.001) and OM (HR = 0.98, 95% CI: 0.97-0.98, p < 0.001) in premenopausal women, but had an adverse effect on the HR of OM (HR = 1.03, 95% CI: 1.02-1.03, p < 0.001) in postmenopausal women. CONCLUSIONS High parity (≥5) was associated with poor breast cancer prognosis in both pre- and postmenopausal women. The time intervals between reproductive events had different effects on breast cancer outcomes depending on menopausal status.