Epidemiology

Breast Cancer Research and Treatment

, Volume 142, Issue 1, pp 165-175

Reproductive factors and risk of premenopausal breast cancer by age at diagnosis: Are there differences before and after age 40?

  • Erica T. WarnerAffiliated withDepartment of Epidemiology, Harvard School of Public HealthChanning Division of Network Medicine, Department of Medicine, Brigham and Women’s Hospital and Harvard Medical School Email author 
  • , Graham A. ColditzAffiliated withDepartment of Epidemiology, Harvard School of Public HealthDepartment of Surgery, Washington University School of Medicine
  • , Julie R. PalmerAffiliated withSlone Epidemiology Center at Boston University
  • , Ann H. PartridgeAffiliated withBreast Oncology Center, Dana-Farber Cancer Institute
  • , Bernard A. RosnerAffiliated withChanning Division of Network Medicine, Department of Medicine, Brigham and Women’s Hospital and Harvard Medical SchoolDepartment of Biostatistics, Harvard School of Public Health
  • , Rulla M. TamimiAffiliated withDepartment of Epidemiology, Harvard School of Public HealthChanning Division of Network Medicine, Department of Medicine, Brigham and Women’s Hospital and Harvard Medical School

Rent the article at a discount

Rent now

* Final gross prices may vary according to local VAT.

Get Access

Abstract

We examined the relationship between reproductive factors and risk of premenopausal breast cancer among women less than age 40 compared with older premenopausal women. We documented 374 incident cases of breast cancer diagnosed before age 40, and 2,533 cases diagnosed at age 40 and older among premenopausal women in the Nurses’ Health Study cohorts. Biennial questionnaires were used to determine age at menarche, age at first birth, parity, breastfeeding, and other reproductive factors. Multivariate relative risks (RR) and 95 % confidence intervals (CI) were calculated using Cox proportional hazards models within age at diagnosis groups. Tumors in younger women were significantly more likely to be higher grade, larger size, and hormone receptor negative than were tumors in older premenopausal women (p < 0.0001). There was no significant heterogeneity according to age in associations between reproductive factors and risk of premenopausal breast cancer. First birth at age 30 or older increased breast cancer risk in both age groups (age <40: RR 1.10, 95 % CI 0.80–1.50; age ≥40: RR 1.16, 95 % CI 1.02–1.32; p-heterogeneity = 0.44). Risk of premenopausal breast cancer decreased with each additional year of age at menarche in both age groups (age <40: RR 0.93, 95 % CI 0.87–0.99; p trend = 0.02; age ≥40: RR 0.94, 95 % CI 0.91–0.97; p trend = <0.0001). Among premenopausal parous women, breastfeeding was protective regardless of age at diagnosis (age <40: RR 0.84, 95 % CI 0.57–1.22; age ≥40: RR 0.85, 95 % CI 0.72–0.99; p-heterogeneity = 0.79). In the largest prospective examination of reproductive risk factors and risk of breast cancer before and after age 40, we found that younger women were more likely to develop tumors with less favorable prognostic characteristics. However, associations between reproductive factors and risk of breast cancer were similar regardless of age at diagnosis of premenopausal breast cancer.

Keywords

Breast cancer Age at diagnosis Young women Reproductive factors