Sex of First Child and Breast Cancer Survival in Young Women

Abstract

Two studies have reported that young women with breast cancer face increased risk of early mortality if their first child was male rather than female. An immunological mechanism has been suggested. We sought to confirm these results in a larger, historical cohort study of 223 parous women who were aged <45 years at breast cancer diagnosis during 1983–1987. Subjects were identified through the Maine Cancer Registry. Follow-up data were obtained from hospitals, physicians, and death certificates. Reproductive history data were obtained from the next of kin of the deceased women, birth certificates, physicians, hospitals, and lastly, subjects. With a 7-year follow-up, multivariate modeling found a lower mortality risk in women with a male first child (hazard ratio [HR] 0.51, 95% confidence interval [CI] 0.32–0.81, log-rank comparison). The survival advantage remained for at least 13 years in women with a male firstborn. Thus, previous studies were not confirmed. Mortality risk in young women with breast cancer is not increased by having borne a male first child rather than a female first child.