Recent changes in breast cancer incidence in Spain, 1980-2004

Abstract

Background: Since the 1980s, Spain experienced two decades of sharply increasing breast cancer incidence. Declines in breast cancer incidence have recently been reported in many developed countries. We examined whether a similar downturn might have taken place in Spain in recent years.

Methods: Cases of invasive female breast cancer were drawn from all population-based Spanish cancer registries that had at least 10 years of uninterrupted registration over the period 1980-2004. Overall and age-specific changes in incidence rates were evaluated using change-point Poisson models, which allow for accurate detection and estimation of trend changes. All statistical tests were two-sided.

Results: A total of 80,453 incident cases of invasive breast cancer were identified. Overall age- and registry-adjusted incidence rates rose by 2.9% (95% confidence interval [CI] = 2.7% to 3.1%) annually during the 1980s and 1990s; there was a statistically significant change in this trend in 2001 (95% CI = 1998 to 2004; P value for the existence of a change point <.001), after which incidence declined annually by 3.0% (95% CI = 1.8% to 4.1%). This trend differed by age group: There was a steady increase in incidence for women younger than 45 years, an abrupt downturn in 2001 for women aged 45-64 years, and a gradual leveling off in 1995 for women aged 65 years or older. Separate analyses for registries that had at least 15 years of uninterrupted registration detected a statistically significant interruption of the previous upward trend in breast cancer incidence in provinces that had aggressive breast cancer screening programs and high screening participation rates, including Navarra (change point = 1991, P < .001), Granada (change point = 2002, P = .003), Bizkaia (change point = 1998, P < .001), Gipuzkoa (change point = 1998, P = .001), and Araba (change point = 1997, P = .002).

Conclusions: The recent downturn in breast cancer incidence among Spanish women older than 45 years is best explained by a period effect linked to screening saturation.

Figure 1

Age- and registry-adjusted incidence rates of invasive breast cancer over the period 1980–2004 among women aged 25 years or older included in all Spanish registries. The observed rates (dotted line) were obtained by using nominal categories for each single calendar year of diagnosis, and the estimated temporal trend (solid line) and its 95% confidence interval (dashed lines) were obtained from fitting a change-point model (see “Methods”).

Figure 2

Age- and registry-adjusted incidence rates of invasive breast cancer over the period 1980–2004 among women who were included in all Spanish registries. A) Women aged 25–44 years. B) Women aged 45–64 years. C) Women aged 65 years or older. The observed rates (dotted lines) were obtained by using nominal categories for each single calendar year of diagnosis, and the estimated temporal trends (solid lines) and their 95% confidence intervals (dashed lines) were obtained from a log-linear model (A) and from change-point models (B and C) (see “Methods”).