Breast cancer incidence and hormone replacement therapy: Results from the MISSION study, prospective phase

Background. The MISSION Study (Menopause: Risk of Breast Cancer, Morbidity and Prevalence) is a historical-prospective study with random patient selection to determine breast cancer incidence in postmenopausal women with or without hormone replacement therapy (HRT). The first prospective follow-up phase started on 5 January 2004 and the cut-off date for data collection was 30 June 2006.Participants. Patients were divided into two groups: an ‘exposed group’ of women on HRT regimens commonly prescribed in France or who had stopped ≤5 years previously; and an ‘unexposed group’ of women who had never received HRT or stopped >5 years previously. In total 6755 patients were included; and prospective data were available for 4949 patients: 2693 in the exposed group and 2256 in the unexposed group. Women in the exposed group were younger, less overweight, and had fewer first-degree family histories of breast cancer than women of the unexposed group. Mean duration of HRT exposure was 8.3 years, with 31% being expos...