Since 1987, the city of Turku, Finland, has offered mammography screening for women aged 40 to 74, biennially for women aged 50 to 74, annually for women aged 40 to 49 born in even calendar years and triennially for women born in odd years. The city of Helsinki and the rest of Finland (with a few exceptions) invited women aged 50 to 59 biennially (national policy). In Finland, the breast cancer incidence follows regional urbanization levels.1 In all study regions, the incidence of breast cancer continued to rise during the screening period.2
The study was conducted to compare the effects of different screening policies on breast cancer mortality in Turku, Helsinki and the rest of Finland (RoF).
The screening effect was evaluated by comparing the cumulative invasive breast cancer (BC) mortality of women aged 40-84 years between the pre-screening period (1976-1986) and the follow-up period 1998-2009 (screening period) in the three regions.
In Turku, the cumulative BC mortality rate was 0.0262 during the screening period and 0.0310 during the pre-screening period, and the risk ratio (RR) was 0.85 (95% CI 0.71-1.00; P=0.055). In Helsinki and in RoF, the rates were approximately the same during the screening period as during the pre-screening period. The rates in Helsinki were 0.0365 and 0.0356, RR=1.01 (95% CI 0.92-1.10; P=0.89) and in RoF 0.0265 and 0.0268, RR=0.99 (95% CI 0.95-1.02; P=0.51), during the screening and pre-screening periods, respectively. Cumulative BC mortality rates are shown in the figure.
Long-term evaluation showed that cumulative breast cancer mortality decreased in Turku, while in Helsinki and in the rest of Finland, it stayed at the previous level. Factors other than the large-scale screening in Turku may also have influenced the difference, which needs further exploration.