Overview

• The Lancet Oncology meta-analysis combined data on 459,476 women aged 16 to 54 to evaluate young-onset breast cancer risk and hormone therapy use.
• Unopposed estrogen therapy was associated with a 14% reduction in breast cancer incidence compared with non-use.
• Estrogen plus progestin therapy corresponded to a 10% increased risk, with the rate rising to 18% after more than two years of use.
• Women who had not undergone hysterectomy or oophorectomy experienced the highest elevated risk with combined therapy.
• Leading health organizations are updating clinical recommendations to help patients and providers tailor hormone replacement decisions based on therapy type and individual history.