Changing pattern of age-specific breast cancer incidence in the Swiss canton of Geneva.

Hormone replacement therapy (HRT) use declined sharply after mid-2002, when the Women's Health Initiative trial reported an association between breast cancer occurrence and HRT. Hypothesized mechanism behind this association is that HRT promotes growth of pre-existing small tumors, leading to earlier tumor detection. We evaluated the impact of the sudden decline in HRT use on age distribution of breast cancer in Geneva.

Remarkable change in age-specific breast cancer incidence in the Swiss canton of Geneva and its possible relation with the use of hormone replacement therapy.

Background: This article aims to explain the reasons for the remarkable change in age of breast cancer occurrence in the Swiss canton of Geneva.

Methods: We used population-based data from the Geneva cancer registry, which collects information on method of detection, stage and tumour characteristics since 1975. For patients diagnosed between 1997-2003, we obtained additional information on use of hormone replacement therapy from a large prospective study on breast cancer.