Nichols HB, et al. - Researchers examined the association of breast cancer risk with recent childbirth and characterized this relation in this pooled analysis of data from 15 prospective cohort studies under the international Premenopausal Breast Cancer Collaborative Group. Study participants included females aged < 55 years. A full 18,826 incident cases of breast cancer were diagnosed during 9.6 million person-years of follow-up. Parous women had an HR for breast cancer that peaked about 5 years after birth before decreasing to 0.77 after 34 years vs nulliparous women. A shift from positive to negative was observed about 24 years after the birth. The investigators 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, parous women were found to have an increased risk of breast cancer for > 20 years after childbirth vs nulliparous women. The researchers advised practitioners to consider recent childbirth as a risk factor for breast cancer in younger parous women.