Jacky Luiten

70 | Chapter 5 allow further refinement, and thus correlations due to the same women being screened more than once could not be modeled. In case the analysis based on CIs enabled clear differentiation of separate periods, such as before (through 2007 and 2008) and after (from 2011 to 2012) introduction of FFDM, pre‐ and postchange outcomes were compared by using chi‐square tests in addition to summary statistics. Interpretation of the tests is exploratory, rather than confirmatory. Preoperative DCIS confirmation was evaluated descriptively only. The median differences and interquartile ranges were calculated for continuous variables. Statistical analyses were performed by using commercially available software (SPSS, version 22.0; SPSS, Chicago, Ill). Results Overall screening results A total of 817,656 mammography screening examinations were performed between January 1997 and January 2017. Of those 817,656 examinations, 97,541 (11.9%) were initial screening examinations and 720,115 (88.1%) were subsequent screening examinations. The median age of recalled women was 59 years (interquartile range, 14). Figure 5.1 shows a flowchart of the study participants. The number of screening examinations increased from 48,721 in 1997–1998 to 131,757 in 2015–2016 (Table 5.1). Of the 817,656 women, 18,592 (2.3%) were recalled for further analysis of a suspicious lesion at mammography screening; the overall recall proportion was 4.7% (95% CI: 4.6%‐4.9%; 4612/97,541) at initial screening examination and 1.9% (95% CI: 1.9%‐1.9%; 13,980/720,115) at subsequent screening examinations. From the trend analysis (Table 5.1), the recall rate for initial screening examinations increased from 2.3% (1039/46,155) during the SFM period (1997‐ 1998) to 5.5% (558/10,182) during the transition period ( p< 0.001) and to 7.3% (3015/41,204) during the FFDM period (2011–2016; p< 0.001). The recall rate for subsequent screening examinations increased in the same period, from 1.1% (3413/304,854) in the SFM period to 2.3% (1801/79,946; p< 0.001) in the transition period and to 2.6% (8766/335,315) in the FFDM period ( p< 0.001; Table 5.1). Combined, these led to an increase of the overall recall rate from 1.3% (4452/351,009) during the SFM period to 3.1% (11,781/376,519) during the FFDM period ( p <0.001).