Nichols HB, et al. – In this pooled analysis of data from 15 prospective cohort studies under the international Premenopausal Breast Cancer Collaborative Group on females aged < 55 years, researchers examined the association of breast cancer risk with recent childbirth. A total of 18,826 incident cases of breast cancer were diagnosed among study participants during a follow-up of 9.6 million person years. Using cox proportional hazards regression, the investigators calculated HRs and 95% CIs. HR for breast cancer came to a head at 5 years post-childbirth before decreasing to 0.77 following 34 years among parous vs nulliparous women. A shift from positive to negative was observed about 24 years after the birth. The overall model was induced by estrogen receptor (ER)–positive breast cancer; no crossover was observed for ER-negative cancer. They noted a more pronounced increase in breast cancer risk after childbirth among those with a family history of breast cancer; increased risk of breast cancer was also greater among those who were older at first birth or who had multiple births. The risk patterns were not altered by breastfeeding. Overall, researchers found that parous women were at increased risk for breast cancer for > 20 years after childbirth vs nulliparous women. They recommended physicians to consider recent childbirth as a risk factor for breast cancer in younger parous women.