Jacky Luiten

Trends in incidence and tumor grade in screen‐detected DCIS and invasive breast cancer | 23 2 Figure 2.1 Rate per 1000 screened women. In the period 2009–2011, during which SFM was gradually replaced by FFDM, the distribution in DCIS proportions differed from previous and subsequent cohorts. Compared to the last SFM‐only period, a shift from high to low grade DCIS was found, leaving the proportion of intermediate DCIS virtually unchanged; (low grade DCIS: 30.6% vs. 16.1%, high grade DCIS: 35.7% vs. 53.8%, p =0.036). The distribution rate by DCIS grade per 1000 screens for both low grade as well as intermediate grade significantly increased during the transition period (low 0.1 vs. 0.5 per 1000 screens ( p ≤0.001); intermediate 0.3 vs. 0.5 per 1000 screens ( p =0.009) whereas the rate of high grade DCIS remained unchanged (0.5 per vs. 0.6 per 1000 screens; p =0.365; Figure 2.1). The transition was characterized by an increased overall CDR of DCIS per 1000 women screened (0.8 vs. 1.6 per 1000 screens; p ≤0.001). In the transitional cohort, when compared to the first FFDM‐only period, a significantly higher proportion of low grade DCIS and lower proportion of high grade DCIS (low grade; 30.6% vs. 18.2% and high grade; 35.7% vs. 48.6%, p =0.013; Table 2.3) were found leaving the proportion of intermediate grade DCIS rather unchanged. The distribution rate by grade per 1000 screened women changed correspondingly; low grade 0.5 vs. 0.3 per 1000 screens ( p =0.017), intermediate grade 0.5 vs. 0.5 per 1000 screens ( p =0.856) and high grade 0.7 vs. 0.6 per 1000 screens ( p =0.084; Figure 2.1). Overall, the two FFDM periods together (2011‐2015) revealed a significantly lower proportion of high grade DCIS as compared to the two SFM periods (2005–2009) 48.7% (168/345) vs. 62.8% (76/121), resulting in a lower proportion of low grade (17.1% vs. 14.0%) and intermediate grade DCIS (34.2% vs. 23.1%, p =0.029). The distribution rate by grade per 1000 women screened increased for low grade (0.1