Effects of screening for breast cancer on its age-incidence relationships and familial risk

Mammographic screening programs for breast cancer have been implemented in many countries and opportunistic mammographies are taken as a diagnostic method. The consequences of the wide application of this technology to age-incidence relationships in breast cancer have not been clarified nor is its effect on familial risk estimation. It was assumed that if screening and diagnostic methods bias familial risk, the highest risk should be noted for sisters diagnosed close in time. Age-specific incidence data were collected from the EUCAN database and from cancer registries of Finland, Norway and Sweden. The Swedish Family-Cancer Database was used to analyse risks for breast cancer among sisters, depending on the time since the first sister was diagnosed with breast cancer. Age-incidence patterns deviated between Germany, with low mammographic coverage, and Sweden, the Netherlands, the UK and France, with variable levels of coverage. The annual age-incidence patterns in Finland, Norway and Sweden changed in concert with the targeted mammographic service. The risk of breast cancer for women with an affected sister, diagnosed between ages 50 to 64 years, was significantly higher within the same or the subsequent year of the sister's diagnosis compared to 5+ years, accounting for 7.3% of all patients. The ordered increase in age-specific incidence of breast cancer in the women targeted by screening studied suggests that mammographic screening is one important factor responsible for the shift of the age of onset for breast cancer towards middle age. However, the effects on the estimation of familial risk are so far small.