Abstract P3-12-37: The impact of the COVID-19 outbreak on breast cancer stage in the Netherlands by screening status

Introduction: The COVID-19 outbreak led to the suspension of the Dutch breast cancer screening program, increased the reluctance of patients to visit the general practitioner (GP), and led to a lack of capacity at the GP. As a consequence, the incidence of breast cancer diagnoses decreased. Objective: This study aimed to investigate the impact of the COVID-19 outbreak on the incidence of different stages of breast cancer, by screening status. Methods: Women diagnosed between January 1^st 2017 and February 28^th 2021 with primary breast cancer without a history of breast cancer were selected from the Netherlands Cancer Registry. March 1^st 2020 till February 28^th 2021 was regarded as the COVID-19 period. Breast cancer incidence within this COVID-19 period was calculated by tumor stage and compared with the incidence in 2017/2019 (reference). Incidence was expressed per 100,000 women aged 18 year or older, living in the Netherlands at the start of the year. Thereafter, the COVID-19 period was divided into four subperiods, based on COVID-19 related events: March-April 2020, May-June 2020, July-August 2020, September 2020-February 2021. Incidence in each of those periods was calculated by tumor stage and compared with the incidence in 2017/2019. Analyses were further stratified by screening status. Incidence of screen-detected tumors was expressed per 100,000 women aged 50-74 living in the Netherlands at the start of the year. Results: A total of 15,916 women were diagnosed in 2017, 15,574 in 2018, 15,867 in 2019, 13,497 in 2020 and 2,532 up to February 2021. Compared to 2017/2019, the incidence of DCIS and stage I-III tumors was statistically significantly lower during the COVID-19 period (32%, 24%, 9% and 11% respectively) (Table 1), leading to 603, 1539, 520 and 160 missed diagnoses respectively. The incidence of stage IV tumors was 5% higher, however this was not significant. The incidence of DCIS remained significantly lower throughout the four subperiods, while the incidence of stage I-II tumors was comparable with 2017/2019 in September 2020-February 2021 and the incidence of stage III was comparable with 2017/2019 in both July-August 2020 and September 2020-February 2021. The incidence of DCIS and stage I-II non-screen-detected tumors was significantly lower during March-April 2020 and was comparable with 2017/2019 in the subperiods thereafter. The incidence of DCIS and stage I-IV screen-detected tumors was significantly lower during March 2020-February 2021, with the incidence of DCIS and stage I-III tumors being lower during each subperiod and the incidence of stage IV tumors being lower during May-June 2020. Conclusion: The COVID-19 outbreak led to a decrease in the incidence of DCIS and stage I-III tumor diagnoses, which still lags behind in February 2021. Until February 2021 no stage shift was seen.

Citation Format: Anouk H Eijkelboom, Sabine Siesling, Linda de Munck, Carla H van Gils, Marc BI Lobbes, Vivianne CG Tjan-Heijnen, Luc JA Strobbe, Jelle Wesseling, Ruud M Pijnappel, Mireille JM Broeders, NABON-COVID-19 consortium, COVID and Cancer Care-NL consortium (ZONMW number10430022010014). The impact of the COVID-19 outbreak on breast cancer stage in the Netherlands by screening status [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-12-37.