Standardisation of stage information collected by European population-based cancer registries: an application to breast cancer survival

Abstract

Background Stage at diagnosis strongly influences breast cancer (BC) prognosis. However, differences in staging systems and incomplete data in European population-based cancer registries (PBCRs) limit international comparisons. We propose a standardized TNM-based stage reconstruction to analyse long-term stage-specific BC survival across Europe. Materials and methods We analysed 714 864 female BC cases diagnosed during 2001-2013 from 23 PBCRs in 14 European countries from the EUROCARE-6 dataset. Stage data were standardized to the seventh TNM edition. Stage was reconstructed into four categories (I-IV). Ten-year relative survival (RS) and 10-year RS conditional on surviving 5 years (CRS10/5) were estimated in the period 2010-2014 using period analysis. Results Availability of stage information for BC ranged from 75% to 99% across countries. Early-stage disease (I-II) represented 80% of known stages, with higher prevalence of stage I in Northern and Central Europe than in Eastern Europe. Overall, 10-year age-adjusted RS decreased from 97% in stage I to 10% in stage IV. Geographic variation was limited for stage I and marked for other stages, with poorer outcomes in Eastern Europe. CRS10/5 showed minimal excess mortality after 5 years for stage I but persistent excess mortality for more advanced stages. Younger women had poorer outcomes than those aged 45-54 years. Conclusions Population-based data on stage for BC confirm the importance of early diagnosis and highlight large disparities in treatment and prognosis across Europe for patients with advanced-stage BC. Improved availability of harmonized stage information at population level is essential for designing and assessing evidence-based cancer control policies.