ESTROGENS AND BREAST CANCER RISK

Summary

Collaborative Group on Hormonal Factors in Breast Cancer. Menarche, menopause, and breast cancer risk: individual participant meta-analysis, including 118 964 women with breast cancer from 117 epidemiological studies. Lancet Oncol2012;13:141-151.

Both menarche and menopause affect breast cancer risk. The aim of this meta-analysis of epidemiological studies was to examine how that relates to the tumor type and the length of reproductive life in the women. Data from 117 studies, which included 118,964 women with invasive breast cancer and 306,091 without the disease, were included. The authors calculated adjusted relative risks (RRs) associated with menarche and menopause for breast cancer overall, and by tumor histology and by estrogen receptor (ER) expression. None of the women had used menopausal hormone therapy.

Breast cancer risk increased by a factor of 1.050 (95% CI, 1.044-1.057; P < 0.0001) for every year younger at menarche, and by a smaller amount (1.029, 1.025-1.032; P < 0.0001), for every year postmenopause. Premenopausal women had a greater risk of breast cancer than postmenopausal women of the same age (RR at ages 45-54 1.43, 1.33–1.52, P < 0.001). All three of these associations were weakened by increasing adiposity among postmenopausal women, but did not vary greatly by women’s year of birth, ethnic origin, childbearing history, smoking, alcohol consumption, or hormonal contraceptive use. All three associations were stronger for lobular than for ductal tumors (P < 0.006 for each comparison). The effect of menopause in women of an identical age and trends by age at menopause were stronger for ER−positive disease than for ER-negative disease (P < 0.01 for both comparisons).

The conclusions of this review were that the length of a woman's reproductive years was not the sole cause of breast cancer risk. The authors feel that endogenous ovarian hormones are more relevant for ER-positive disease than for ER-negative disease and for lobular than for ductal tumors.