Background: Generally, screen-detected cancers have more favourable tumour characteristics than clinically detected or symptomatic cancers. Less is known, whether the tumour characteristics of breast cancer have changed over time into more favourable in general and whether the changes have been similar in all ages.
Material and methods: The aim of this study was to explore the change of breast cancer characteristics in parallel to the implementation of modern diagnostic methods in three age groups over four 5-year time periods between 1992 and 2011. The data from 942 primary breast cancers in one university hospital district in Finland were combined with data from the Finnish Cancer Registry and the Mass Screening Registry. The association of favourable tumour characteristics with time period, age group and diagnostic methods was explored.
Results: The most discernible secular change was the increase in oestrogen (ER)-positive cancers in every consecutive time period. The risk for ER positivity in the second, third and fourth period was 2- to 2.71-fold compared to the first period. An increase in small tumours and node-negative tumours was detected during the most recent years of data collection. The secular changes were observed in all age groups; however, overall ER positivity was most frequent among women beyond screening age and small tumours among screening-aged women. The increase in small and node-negative tumours could partly be explained by the implementation of new radiological methods.
Conclusions: This study detected a secular change of tumour characteristics into more favourable irrespective of age group. If the trend continues, it seems that we are going to have a breast cancer population of mainly small ER-positive breast cancers in the future forcing to rethink the therapeutic approach.