Body Mass Index, Age, and Premenopausal Breast Cancer Risk


Key Points

  • An inverse relation between BMI and premenopausal cancer risk was found across all BMI categories.
  • The association was strongest in the younger age groups.

In a multicohort study reported by researchers from the Premenopausal Breast Cancer Collaborative Group in JAMA Oncology, Schoemaker et al found that increasing adiposity was associated with a significantly reduced risk of premenopausal breast cancer across the entire spectrum of body mass index (BMI).

The study used pooled individual-level data from 758,592 premenopausal women from 19 prospective cohorts to estimate risk of premenopausal invasive or in situ breast cancer according to BMI from ages 18 to 54 years using Cox proportional hazards regression analysis. Analysis was adjusted for attained age, cohort, year of birth, age at menarche, age at first birth, time since last birth, parity, and family history of breast cancer.

Participants were recruited from January 1963 through December 2013, and data were analyzed from September 2013 through December 2017. Risk was assessed by BMI at ages 18­ to 24, 25 to 34, 35 to 44, and 45 to 54 years. Participants had a median age of 40.6 years.

Inverse Association of Risk

Median follow-up was 9.3 years (interquartile range = 4.9–13.5 years) per participant, with 13,082 incident cases of breast cancer being identified. Inverse linear associations of BMI with breast cancer risk were identified across all BMI categories, with the association being strongest at younger ages.

For example, the hazard ratio [HR] per 5 kg/m2 increase in BMI at ages 18 to 24 years was 0.77 (95% confidence interval [CI] = 0.73–0.80) compared with 0.88 (95% CI = 0.86–0.91) at ages 45 to 54 years. Significant differences in risk were present even within the normal range of BMI (HR = 0.80, 95% CI =0.75–0.86, for 23.0–24.9 vs 18.5–22.9 kg/m2). In the 18– to 24-year-old age group, there was a 4.2-fold risk gradient from highest to lowest BMI category; eg, risk was reduced by 76% for BMI ≥ 35.0 vs < 17.0 kg/m2 (HR = 0.24, 95% CI = 0.14–0.40).

The inverse associations were stronger for estrogen receptor–positive and/or progesterone receptor–positive vs hormone receptor–negative breast cancer for BMI at every age group; thus, for example, for BMI at age 18 to 24 years, the hazard ratio per 5 kg/m2 difference was 0.76 (95% CI = 0.70–0.81) for estrogen receptor–positive and progesterone receptor–positive tumors vs 0.85 (95% CI = 0.76–0.95) for hormone receptor–negative tumors. No consistent association of BMI at ages 25 to 54 years was observed for triple-negative or hormone receptor–negative breast cancer overall.

The investigators concluded, “The results of this study suggest that increased adiposity is associated with a reduced risk of premenopausal breast cancer at a greater magnitude than previously shown and across the entire distribution of BMI. The strongest associations of risk were observed for BMI in early adulthood. Understanding the biological mechanisms underlying these associations could have important preventive potential.”

This study was supported by Breast Cancer Now and the United Kingdom National Health Service funding to the Royal Marsden/Institute of Cancer Research National Institute for Health Research Biomedical Research Centre, The Institute of Cancer Research, and others.

Minouk J. Schoemaker, PhD, of the Division of Genetics and Epidemiology, The Institute of Cancer Research, London, is the corresponding author for the JAMA Oncology article.

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.