Learning from temporal relationships: Childbirth and breast cancer risk
A partir de données de 15 études prospectives, cette étude évalue l'association entre un accouchement récent et le risque de cancer du sein (période de suivi : 9,6 millions personnes-années ; âge : inférieur à 55 ans ; 18 826 cas)
The relationship between childbirth and breast cancer risk is complex. Childbirth is an intrinsically multidimensional “exposure,” and understanding its effects requires disentangling age, parity, use of contraceptive and reproductive technology, and breastfeeding, among other factors. Given this complexity, the results of the large and sophisticated analysis by Nichols and colleagues (1) provide an important advance in this field. In this examination of nearly 900 000 women aged younger than 55 years who were enrolled in studies of premenopausal breast cancer, risk for breast cancer peaked 5 years after childbirth and then gradually decreased for at least 2 decades. Because of the large study population, the investigators could also examine important subgroups: The effect was not seen for women who had only 1 child or had their first child before age 25 years, and it was greatest for estrogen receptor–negative cancer and among women with a family history of breast cancer