Abstract S02-02: The impact of resuming the breast cancer screening program in the Netherlands on breast cancer incidence and stage after its discontinuation due to the COVID-19 pandemic

Introduction: The burden of the COVID-19 pandemic forced the Dutch health care services to discontinue their national screening programs on 16 March 2020 (week 12). For breast cancer, the program invites women aged 50–74 years for biennial screening mammography. From mid-June 2020 (week 25) the breast cancer screening program was resumed, albeit with reduced capacity (max 60%). We aimed to investigate the impact of resuming the screening program on incidence, tumor-, and T-stage of screen- and non-screen-detected ductal carcinoma in situ (DCIS) and invasive breast cancer (IBC) in the Netherlands. Methods: Women, 50-74 years of age, diagnosed with DCIS or IBC in weeks 2–35 of 2018, 2019 and 2020 were selected from the Netherlands Cancer Registry. Weekly incidence of screen- and non-screen-detected tumors was calculated and expressed per 1 million women aged 50-74 years living in the Netherlands. Weeks 2-35 were divided in seven periods, representing separate phases of the pandemic. For each period, incidence of screen- and non-screen-detected tumors was stratified by clinical tumor stage (TNM) and clinical T-stage. Incidence in each period of 2020 was compared with the incidence in the same period of 2018/2019 (averaged). Results: In weeks 2-35, 7,250 patients were diagnosed in 2018, 7,299 in 2019, and 5,300 in 2020. During weeks 2-12 2020 the weekly average incidence of screen-detected tumors was 42/1 million women aged 50-74. In week 13 incidence dropped to 19, and was almost zero during weeks 14-25. Incidence increased to 4 in week 26, when the screening was gradually restarted, and increased to an weekly average of 24 tumors/1 million in weeks 30-35, when screening had restarted in most of the Netherlands. During weeks 14-16, 17-25, 26-29, and 30-35 2020 incidence of screen-detected DCIS, stage I-II tumors and T0-2 tumors was lower than in the same period of 2018/2019. Distribution of tumor- and T-stage in newly diagnosed tumors did not differ between the periods (24% DCIS, 57% stage I, 18% stage II, 1% stage III, 1% stage IV; 24% T0, 59% T1, 15% T2, 2% T3, 0% T4). During weeks 2-11 2020 the weekly average incidence of non-screen-detected tumors was 38/1 million women aged 50-74. Incidence dropped to 16 in week 14, and increased to an average of 37 tumors per week in weeks 17-35. During weeks 17-25, 26-29, and 30-35 the incidence and distribution of non-screen-detected DCIS, stage I-IV and T0-4 tumors was comparable with 2018/2019 (weekly incidence (distribution): 3 DCIS (9%), 15 stage I (40%), 13 stage II (36%), 3 stage III (7%), 3 stage IV (8%); 3 T0 (9%), 17 T1 (45%), 12 T2 (34%), 3 T3 (8%), 2 T4 (5%)). Conclusion: The temporary suspension of the breast cancer screening program reduced the incidence of breast cancer. After resuming screening the incidence did not raise above the incidence in 2018/2019, therefore it is expected that the incidence will rise during the next months. The results to date did not show a shift towards a higher tumor stage or T-stage. Citation Format: Anouk H. Eijkelboom, Linda de Munck, Marc B.I. Lobbes, Jelle Wesseling, Carla H. van Gils, Pieter J. Westenend, Cristina Guerrero Paez, Ruud M. Pijnappel, Helena M. Verkooijen, Mireille J.M. Broeders, Sabine Siesling. The impact of resuming the breast cancer screening program in the Netherlands on breast cancer incidence and stage after its discontinuation due to the COVID-19 pandemic [abstract]. In: Proceedings of the AACR Virtual Meeting: COVID-19 and Cancer; 2021 Feb 3-5. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(6_Suppl):Abstract nr S02-02.