The publication of a major analysis in the Lancet, involving combined data from 58 studies and more than 100,000 patients, suggesting the risk of breast cancer from taking HRT is twice that originally thought, will concern many women.

The Collaborative Group on Hormonal Factors in Breast Cancer study focused on the long-term effects of HRT and examined particularly age at first use, duration of use, and time elapsed since last use. It is an intricately designed study.