Bröstcancer i Sverige: Trender och regionala skillnader i incidens

Sammanfattning: This paper sets out to investigate trends and regional differences in breast cancer incidence, in the 21 regions of Sweden between the years 1970 and 2020. Breast cancer is the most common cancer type among women, accounting for around 30% of all cases. The National Board of Health and Welfare estimates that 1 in 10 women will experience breast cancer before the age of 75. This has significant public health implications, including increasing treatment costs and loss of income. Understanding trends in incidence has a crucial importance given the tremendous suffering the disease causes the society, both emotional and economical. Better understanding of trends in breast cancer can allow necessary steps to be taken in line with public interventions. The healthcare policies in Sweden are determined on a regional level. This creates the setting of a natural experiment, where the efficiency of different policies can be evaluated by identifying and investigation regional variations. Age-standardised incidence rates (ASIR) are modelled for the age groups 20–39, 40–74, 75+ and 20–85+ using Local Polynomial regression fitting (LOESS). Regional variations are identified by calculating absolute and relative differences. Relative change in each region is calculated to quantify differences in morbidity between 1970 and 2020. Results show increasing trends in all regions and considerable regional variations that seems to intensify through time. High incidence levels are observed in several of the regions in the south for all age groups. The average regional increase in ASIRLOESS was 120% (95% CI: 105.1, 135.5) for women 20–85+. The region of Norrbotten experienced the largest relative change in rates with an increase of 233%. The smallest relative change occurred in the region of Värmland with an increase of 71%. The age group 20–39 experienced the largest relative increase in ASIRLOESS with an average of 165% (95% CI: 108.3, 221,6). Mammographic screening has resulted in a shift in the age-distribution of women at time of diagnosis. All regions experienced an increase in the share of incidence cases in the age group included by the screening interval (40–74 years old) and a decrease in women 75 years or older. Most regions also experienced an increase in the share of women below 40. However, the regions of Sörmland, Kronoberg, Dalarna, and Jämtland Härjedalen had a smaller share of women under 40 in 2020 compared to 1970. These findings indicate large regional variations. Further research needs to be conducted to find what is causing differences among regions.