paywalled: Conjugated equine oestrogen and breast cancer incidence and mortality in postmenopausal women with hysterectomy: extended follow-up of the Women's Health Initiative randomised placebo-controlled trial : The Lancet Oncology

Conjugated equine oestrogen and breast cancer incidence and mortality in postmenopausal women with hysterectomy: extended follow-up of the Women's Health Initiative randomised placebo-controlled trial : The Lancet Oncology

 Interpretation

Our findings provide reassurance for women with hysterectomy seeking relief of climacteric symptoms in terms of the effects of oestrogen use for about 5 years on breast cancer incidence and mortality. However, our data do not support use of oestrogen for breast cancer risk reduction because any noted benefit probably does not apply to populations at increased risk of such cancer.

Commentary: Oestrogen and breast cancer: results from the WHI trial : The Lancet Oncology

Oestrogen and breast cancer: results from the WHI trial : The Lancet Oncology

"In The Lancet Oncology, the Women's Health Initiative (WHI) investigators report1 that receipt of conjugated equine oestrogen for a median of 5·9 years reduced the risk of invasive breast cancer by 23% compared with placebo (151 cases in 5310 women who received oestrogen vs 199 cases in 5429 controls; p=0·02). Women who did develop breast cancer after receipt of oestrogen had significantly reduced breast cancer-specific mortality (six deaths in the oestrogen group vs 16 deaths in controls; p=0·03) and all-cause mortality (30 deaths vs 50 deaths; p=0·04). This preventive effect occurred at all ages and continued beyond the period of oestrogen use, a carryover effect also noted in prevention trials of tamoxifen.2 ....Although modest, the WHI results are significant and raise important questions about their disparity with many observational studies and the mechanism of reported benefit with oestrogen therapy......