Trends in incidence of ductal carcinoma in situ: The effect of a population-based screening programme

Background: The incidence of ductal carcinoma in situ (DCIS) has increased substantially in the western world in recent decades. The aim of this study was to investigate the incidence according to grade distribution, age, and implementation of a population-based screening programme. Methods: Cases of primary pure DCIS (n ¼ 3167) were obtained from the Cancer Registry of Norway. Poisson regression was used to estimate trends in incidence. Results: Age-adjusted incidence of DCIS increased from 4 to 11 per 100 000 women-years from 1993 to 2007, in parallel with the implementation of screening. Higher incidence was observed among prevalent (IRR 3.3) and subsequent (IRR 2.8) invited women compared with those not invited. The proportion of DCIS among breast malignancies increased throughout the period, most markedly in the age range of screening. Conclusion: The increased proportion of DCIS during the study period is probably due to improved diagnostics resulting from the implementation of population-based screening.