BACKGROUND AND PURPOSE:

• Increased BMI in postmenopausal women is associated with increased risk for breast cancer
• Limitations in previous studies that assessed risk of adiposity in premenopause (case reports/small sample size)
• The Premenopausal Breast Cancer Collaborative Group (JAMA Oncology, 2018) examined how BMI at different ages is associated with premenopausal breast cancer risk

METHODS:

• Multicenter Prospective Cohort Study
  • Pooled individual-level data from 19 prospective cohorts
• BMI was recorded from ages 18-54 years
• Median follow-up was 9.3 years per participant and incidence of breast cancer was recorded
• Primary outcome: Invasive or in situ premenopausal breast cancer

RESULTS:

• 758,592 premenopausal women were included
  • 13,082 incident cases of breast cancer
• BMI at ages 18 to 24 years compared to ages 45 to 54 years demonstrated a stronger inverse linear association with breast cancer risk
  • Age 18 to 24: Hazard risk (HR) per 5 kg/m2 (5.0-U) difference 0.77 (95% CI, 0.73-0.80)
  • Age 45 to 54: HR per 5.0-U difference, 0.88 (95% CI, 0.86-0.91)
• Risk gradient between the highest and lowest BMI categories (BMI≥35.0 vs <17.0)
  • There was a 4.2-fold risk between ages 18 to 24 years
  • HR, 0.24 (95% CI, 0.14-0.40)
• The inverse associations between BMI and breast cancer risk were consistent
  • Among nonoverweight BMI levels
  • Taking in to account other breast cancer risk factors
• BMI at every age group was most strongly associated with ER and/or PR positive breast cancer

CONCLUSION:

• Greater BMI is associated with a reduced risk of premenopausal breast cancer
• Associations were strongest for early adult BMI
• The authors have “estimated 12% to 23% reduction in premenopausal breast cancer risk per 5 kg/m2 difference in BMI”
• The authors do not recommend adiposity as a preventative measure.  It rather reflects underlying hormonal mechanisms that need to be further elucidated

Learn More – Primary Sources:

Association of Body Mass Index and Age With Subsequent Breast Cancer Risk in Premenopausal Women

Related ObG Topics:

ACOG Practice Advisory: Counseling Patients About Breast Cancer Risk and Hormonal Contraception

A Breast Cancer Diagnosis in the Interval Between Mammograms: Who is at Risk?

Breast Cancer Risk Assessment for Average Risk Women – The 5-Year Risk Score