Background: Female breast cancer incidence rates have been increasing in Portugal for years. We, therefore, conducted the first nationwide breast cancer study to assess regional differences.
Methods: Cases were obtained from population-based cancer registries covering the country's Mainland (South, North, Centre), as well as the two Autonomous Regions (Azores and Madeira), for the time-period 1998 through 2011. Analyses were restricted to ages 30-84 years and stratified by region. We used the age-period-cohort (APC) framework to complement standard descriptive techniques and to forecast future trends. Estimable APC parameters included net drift, longitudinal age-specific incidence rate curves, and fitted age-specific incidence rate ratios.
Results: There were 71 545 breast cancer cases diagnosed in Portugal at ages 30-84 years from 1998 to 2011. The South presented the highest age-standardized rate (155.8/100 000), while the North presented the fastest rate of increase (3.6%/year). Age-specific statistical interactions were observed between regions. Younger women in the North revealed a decreased risk of developing breast cancer compared to women from the same age group in the South and Centre, while that risk was reversed in older women (p < 0.05). We estimate that from 2014 onwards, the North might rank first among all regions.
Conclusion: The variant patterns observed could be due to a combination of different screening practices and/or exposure to risk factors across regions. Disease heterogeneity among younger and older women may also explain part of the differences in age-specific rates. These results justify continued monitoring of breast cancer incidence by region.
Keywords: Breast cancer; Incidence; Portugal; Trends.
Copyright © 2018 Elsevier Ltd. All rights reserved.