Jacky Luiten

24 | Chapter 2 vs. 0.2 per 1000 screens; p <0.001) and intermediate grade (0.2 vs. 0.5 per 1000 screens; p <0.001), in contrast to high grade DCIS (0.6 vs. 0.7 per 1000 screens; p =0.232). DCIS: initial versus subsequent screens Table 2.4 shows the DCIS proportions, according to histological grade, at initial and subsequent screening mammography. A total of 623 DCIS lesions were detected (113 initial screen, 510 subsequent screens). The combined proportions of intermediate and high grade DCIS were significantly higher at subsequent screening than at initial screening; 70.7% (80/113) vs. 80.2% (419/510; p =0.023). Invasive carcinoma Invasive carcinoma was diagnosed in 2436 recalls (79.6% of all screen‐detected cancers; Table 2.1). The abnormality most frequently presented itself as a suspicious mass at screening mammography (71.3%, Table 2.2). The majority of these breast cancers were low grade (45.4%; 1106 women) or intermediate grade (41.6%; 1013 women). The proportional distribution by grade was comparable for both SFM‐only cohorts ( p =0.126; Table 2.3). The invasive carcinoma rate per 1000 women screened was comparable when analyzed according to grade; low grade 2.0 vs. 1.7 per 1000 screens ( p =0.287), intermediate grade 1.3 versus 1.8 per 1000 screens ( p =0.050) and high grade 0.5 versus 0.6 per 1000 screens ( p =0.473; Figure 2.1). In the two consecutive FFDM‐only cohorts (2011‐2013 vs. 2013‐2015), the proportional distribution by grade was also comparable ( p =0.240; Table 2.3). The rate per 1000 women screened according to grade was comparable for low grade 2.4 vs. 2.4 per 1000 screens ( p =0.810) and high grade 0.7 vs. 0.5 per 1000 screens ( p =0.545). However, the difference with regard to intermediate grade invasive carcinomas was significantly different; 2.1 vs. 2.6 per 1000 screens ( p =0.008; Figure 2.1). The proportion of low grade invasive carcinoma was higher in the transition cohort (2009‐2011) as compared to the last SFM cohort (2007‐2009) (50.1% vs. 41.3%, p =0.003). This resulted into a lower proportion of high grade invasive carcinoma (14.1% vs. 7.5%, p=0.003). The transition was also characterized by an increased overall CDR of invasive carcinoma per 1000 women screened (5.1 vs. 4.1; p =0.003) mainly due to an increased detection rate of low grade invasive carcinoma per 1000 women screened (2.6 vs. 1.7 per 1000 screens; p ≤0.001).