Overview

• Oestrogen-only therapy was linked to a 14% reduction in young-onset breast cancer risk, with stronger protection when started at younger ages or used longer.
• Combined oestrogen-progestin therapy was associated with a 10% increased breast cancer risk, rising to 18% after more than two years of use.
• Women with an intact uterus or ovaries experienced higher risk from combined therapy compared to those who had undergone hysterectomy or oophorectomy.
• The Lancet Oncology meta-analysis pooled data from 459,476 women aged 16 to 54 across North America, Europe, Asia and Australia.
• Health bodies and clinicians are integrating these findings into personalized guidelines, affirming unopposed oestrogen only for post-hysterectomy patients.