Purpose: The time interval between last childbirth and subsequent breast cancer diagnosis is emerging as an important prognostic factor for premenopausal women.
Patients and methods: We studied, prospectively, 750 women diagnosed with primary invasive breast cancer before age 45 years who participated in the population-based Australian Breast Cancer Family Study (ABCFS).
Results: Median follow-up time was 4.9 years (range, 0.8 to 10.8 years). Compared with nulliparous women, women who gave birth within 2 years prior to diagnosis were more likely to have axillary node-positive (58% v 41%; P =.01), and estrogen receptor-negative (58% v 39%; P =.005) tumors. The unadjusted hazard ratios for death were 2.3 (95% CI, 1.3 to 3.8; P =.002), 1.7 (95% CI, 1.1 to 2.6; P =.03), and 0.9 (95% CI, 0.6 to 1.5; P =.8) for patients who gave birth less than 2 years, 2 to 5 years, and 5 or more years before diagnosis, respectively. After adjusting for tumor characteristics, these hazard ratios were reduced to 1.9 (95%CI, 1.1 to 3.2; P =.02), 1.3 (95% CI, 0.8 to 2.1; P =.3), and 0.9 (95%CI, 0.5 to 1.4; P =.5). Modeling showed that, compared with nulliparous women, the mortality hazard ratio in parous women was 1.9, decreasing by 8% (95%CI, 4% to 13%; P <.001) for each year between last birth and breast cancer diagnosis.
Conclusion: Proximity of last childbirth to subsequent breast cancer diagnosis is a predictor of mortality independent of histopathological tumor characteristics. Clinicians should be aware that women diagnosed with breast cancer within a few years following childbirth may have a worse outcome than that suggested solely by the standard histopathological prognostic factors of their cancer.