1. Unopposed estrogen therapy may reduce breast cancer risk in women under 55.
2. Estrogen plus progestin therapy is linked to an increased risk of breast cancer.
3. Study involved 459,476 women and 8455 cases of young-onset breast cancer.
4. Median follow-up of 7.8 years.
5. Risk reduction strongest in long-term and early initiators of unopposed estrogen. 

Source: The Lancet Oncology