Geographic disparities of breast cancer incidence in Portugal at the district level: A spatial age-period-cohort analysis, 1998-2011.

Froelicher, Joseph H; Forjaz, Gonçalo; Rosenberg, Philip S; Chernyavskiy, Pavel

BACKGROUND Breast cancer is the most common malignancy in women world-wide and the most common cause of cancer deaths, which can often be managed with early diagnosis and subsequent treatment. Here, we focus on geographic disparities in incidence within Portugal for three age groups of women (30-49; 50-69; 70-84 years). METHODS Age-period-cohort (APC) models are widely used in cancer surveillance, and these models have recently been extended to allow spatially-varying effects. We apply novel spatial APC models to estimate relative risk and age-adjusted temporal trends at the district level for the 20 districts in Portugal. Our model allows us to report on country-wide trends, but also to investigate geographic disparities between districts and trends within districts. RESULTS Age-adjusted breast cancer incidence was increasing over 1998-2011 for all three age groups and in every district in Portugal. However, we detect spatially-structured between-district heterogeneity in relative risk and age-adjusted trends (Net Drifts) for each of the three age groups, which is most pronounced in the highly-screened (50-69yo) and late-onset (70-84yo) groups of women. CONCLUSIONS We present evidence of disparities in breast cancer incidence at a more granular geographic level than previously reported. Some disparities may be due to latent risk factors, which cannot be accounted for by age, birth year, and geographic location alone. IMPACT Our study motivates resuming data collection for breast cancer incidence at the district level in Portugal, as well as the study of exogenous risk factors.