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

Abstract

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. We included all incident breast cancer cases recorded from 1975 to 2006 at the Geneva cancer registry. We calculated mean annual incidence rates per 100,000 for 2 year periods for three age groups and assessed temporal changes by joinpoint regression. We compared age-specific incidence curves for different periods, reflecting different prevalence rates of HRT use. After increasing constantly between 1986 and 2002 among women aged 50-69 years [annual percent change (APC): +4.4, P < 0.0001], rates declined sharply after 2003 (APC: -6.0; P = 0.0264). Age-specific breast cancer rates changed dramatically with changes in prevalence of HRT use. During low HRT prevalence, breast cancer incidence increased progressively with age, when HRT prevalence was reaching its maximum (1995-2002), higher rates were seen in 60- to 64-year-old women, with a concomitant decrease in risk among elderly. After the sudden decline in HRT use, the incidence peak diminished significantly and incidence increased again with age. Following the abrupt decline in HRT use in Geneva, breast cancer incidence rates among post-menopausal women decreased considerably with striking changes in age-specific incidence rates before, during and after the peak in HRT prevalence.

Reductions in use of hormone replacement therapy: effects on Swedish breast cancer incidence trends only seen after several years

“…In an analysis based on data from nine US cancer registries, Ravdin et al reported a 7% overall decrease in incidence between 2002 and 2003 in women older than 50 years of age and particularly for estrogen receptor positive tumors [1]. Subsequent studies from the US, Canada, Australia, France, Switzerland, Germany, Great Britain, Belgium, and the Nordic countries have also reported reductions in breast cancer incidence [2][3][4][5][6][7][8][9][10][11][12][13][14]. These changes have been hypothesized to be a result of a dramatic decline in the use of hormone replacement therapy (HRT) following the 2002 release of the report from the Women's Health Initiative (WHI) hormone trial [15].…”

Does hormone replacement therapy (HRT) cause breast cancer? An application of causal principles to three studies

“…From 2000 to 2006, among women aged 50–69 years the rates hardly changed; in the ≥70-year age group the rates were unstable, presumably because of limited numbers. Other findings reported from Switzerland46 47 were based on small numbers, and the rates were unstable.…”

Is The Age-Period-Cohort Model Well Suited to an Epidemic Context? The Case of the French BSE Epidemic

“…It is likely that for chronic diseases, unexpected period effects -when statistically significant -have little impact on the estimation of age and cohort effects and is often ignored as it is the source of relatively small variations (Remontet et al, 2003). However, as shown in recent studies on breast cancer incidence (Ravdin et al, 2007;Bouchardy et al, 2010), sudden changes in chronic disease incidence can be observed over a short period of time. In the situation where a period effect is expected due to simultaneous changes in the exposure of all cohorts or variations in disease surveillance, it is possible that the period effect is overestimated if such changes lead to sudden variations in disease incidence within a short period of time, potentially resulting in a poor estimate of the trend and/or incidence of the disease and in inadequate public health decisions.…”