Abstract P3-12-37: The impact of the COVID-19 outbreak on breast cancer stage in the Netherlands by screening status
Authors: Eijkelboom Anouk H , Siesling Sabine , de Munck Linda , van Gils Carla H , Lobbes Marc BI , Tjan-Heijnen Vivianne CG , Strobbe Luc JA , Wesseling Jelle , Pijnappel Ruud M , Broeders Mireille JM ,   NABON-COVID-19 consortium,   COVID and Cancer Care-NL consortium (ZONMW number10430022010014)
Published: March 2022

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 1st 2017 and February 28th 2021 with primary breast cancer without a history of breast cancer were selected from the Netherlands Cancer Registry. March 1st 2020 till February 28th 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.

Incidence of breast cancer diagnoses per tumor stage and screening statusDCISStage IStage IIStage IIIStage IVReference126.590.876.820.411.0COVID-19 period218.069.269.518.111.5March - April reference14.515.112.73.61.8March - April 20202.28.18.48.41.4May - June reference14.115.413.83.71.9May - June 20201.57.510.52.91.9July - August reference14.315.413.13.31.9July - August 20202.310.711.63.42.2September - February reference113.644.937.39.85.4September 2020 - February 202112.042.939.09.26.0Non-screen-detectedDCISStage IStage IIStage IIIStage IVReference18.841.258.817.910.4COVID-19 period27.639.958.016.611.2March - April reference11.46.99.73.11.7March - April 20200.95.07.02.61.4May - June reference11.67.610.83.11.9May - June 20201.47.210.52.91.9July - August reference11.36.910.03.01.8July - August 20201.16.910.23.22.1September - February reference14.519.828.28.55.1September 2020 - February 20214.320.830.38.05.8Screen-detected3DCISStage IStage IIStage IIIStage IVReference145.3127.146.36.31.3COVID-19 period226.374.127.02.90.6March - April reference18.021.07.51.20.2March - April 20203.58.03.30.20.1May - June reference16.520.17.51.10.2May - June 20200.30.70.20.10.0July - August reference17.621.78.00.80.3July - August 20203.29.73.60.40.1September - February reference123.364.323.33.30.7September 2020 - February 202119.355.819.92.20.4Incidence is expressed per 100,000 women living in the Netherlads Bold: the incidence in that period of 2020/2021 is statistically significantly lower/higher compared to the incidence in the same period of 2017/2019 (averaged) 1. Reference period: 2017/2019 2. COVID-19 period: March 2020 -February 2021 3. Expressed per 100,000 women aged 50-74 years

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.