Abstract PS7-88: Effect of the COVID-19 pandemic on the initial treatment of breast cancer in the Netherlands: A population-based study
Authors: Eijkelboom Anouk H , de Munck Linda , Vrancken Peeters Marie-Jeanne , Smidt Marjolein , Broeders Mireille , Bos Monique , Schmidt Marjanka K , Bessems Maud , Strobbe Luc , van den Bongard Desirée , Honkoop Aafke , Verloop Janneke , Paez Cristina Guerrero , Lobbes Marc , Linn Sabine , Westenend Pieter , Menke-van der Houven van Oordt Catharina W , Wesseling Jelle , Tjan Heijnen Vivianne , Siesling Sabine ,   On behalve of the NABON COVID-19 consortium
Published: February 2021

Introduction The COVID-19 pandemic led to a significant drop in the incidence of cancer diagnoses in the Netherlands, partially due to the suspension of all national cancer screening programs on 16th March 2020 (week 12). Hospitals were forced to focus on care for COVID-19 patients resulting in limited capacity and down scaling of health care for non-COVID-19 patients. Specific recommendations for breast cancer treatment strategies, such as alterations in sequence, type, and/or frequency, were temporarily implemented from week 12 onwards. The aim of this study was to investigate the impact of the first outbreak on the initial treatment of breast cancer patients.

Methods Women older than 18 years, treated within three months following their breast cancer diagnosis during weeks 2-17 2018-2019 (reference period) or weeks 2-17 2020 (COVID-19 period), were selected from the Netherlands Cancer Registry. Weeks 2-17 2020 were split up in four periods, based on the number of breast cancer diagnoses: weeks 2-8, weeks 9-11, weeks 12-13, and weeks 14-17. Average number of breast conserving surgeries (BCS), mastectomies with direct reconstruction (DR), mastectomies without DR, chemotherapy, endocrine therapy or other therapies, given as initial treatment per week, were calculated, stratified by period and by tumor stage. Treatments given to patients diagnosed in the reference period were compared with treatments given to patients diagnosed in the COVID-19 period, using a Mantel-Haenszel test, adjusting for age.

Results A total of 16,553 patients were included in the current study. Of these patients 5,504 received their initial treatment in weeks 2-17 2018, 5,641 in weeks 2-17 2019 and 5,408 in weeks 2-17 2020. An increase in the use of endocrine therapy was seen in weeks 12-13 and 14-17 2020 compared to weeks 2-17 2018/2019, especially for patients with stage I cancer (12.3% and 7.7% vs 4.8%) and stage II cancer (25.4% and 17.4% vs 13.4%). In addition, a lower proportion of patients with stage II breast cancer received chemotherapy as first treatment in weeks 12-13 (21.1%) and 14-17 2020 (20.1%) compared to weeks 2-17 2018/2019 (29.8%) (Table).

Discussion The COVID-19 pandemic led to a major increase in the use of endocrine therapy following the recommendations, which was mainly used to enable postponing surgery. The lower use of chemotherapy was probably related to the thought to limit hospital visits and the expected higher risk of developing COVID-19 complications due to chemotherapy. Possible long-term effects of changes in initial treatments will be monitored.

Foodnote by table: Weeks 2-17 2020 (the COVID-19 period) were compared to the same weeks in 2018-2019, adjusted for age (&lt;40, 40-50, 50-65, 65-74, &gt;74). A statistically significant: ↑ higher proportion of patients received this therapy, corrected for age; ↓ lower proportion of patients received this therapy, corrected for age; a: lower proportion of patients aged between 50 and 64 years received BCS; b: higher proportion of patients aged 39 or younger received mastectomy without DR; c: higher proportion of patients aged 39 or younger, or aged between 50 and 75 years received endocrine therapy; d: higher proportion of patients aged between 40 and 74 years received endocrine therapy; e: higher proportion of patients aged 74 or younger received endocrine therapy; f: higher proportion of patients aged 39 or younger received chemotherapy; g: higher proportion of patients aged 75 years or older received BCS

Average number (percentage) initial treatments per week, stratified by stage and periodTotalBreast conserving surgeryMastectomy with direct reconstructionMastectomy without direct reconstructionChemotherapyEndocrine therapyTotalDCISWeek 2-17 2018/201940.629.5 (72.7)4.9 (12.0)5.7 (13.9)0.1 (0.2)0.3 (0.8)0.1 (0.2)Week 2-8 202043.730.9 (70.6)5.0 (11.4)7.3 (16.7)0.4 (1.0)0.1 (0.3)0.0 (0.0)Week 9-11 202038.027.0 (71.1)4.0 (10.5)7.0 (18.4)0.0 (0.0)0.0 (0.0)0.0 (0.0)Week 12-13 202048.031.5 (65.6)7.0 (14.6)7.0 (14.6)0.0 (0.0)2.5 (5.2) ↑0.0 (0.0)Week 14-17 202028.319.0 (67.3)3.0 (10.6)5.8 (20.4) ↑0.0 (0.0)0.5 (1.8)0.0 (0.0)Stage IWeek 2-17 2018/2019146.2104.5 (71.5)10.0 (6.8)17.8 (12.2)6.2 (4.3)7.0 (4.8)0.7 (0.5)Week 2-8 2020148.4107.9 (72.7)7.0 (4.7) ↓15.3 (10.3)10.0 (6.7) ↑7.4 (5.0)0.9 (0.6)Week 9-11 2020131.793.7 (71.1)8.0 (6.1)14.3 (10.9)6.3 (4.8)8.0 (6.1)1.3 (1.0)Week 12-13 2020163.0107.5 (66.0)a10.0 (6.1)20.0 (12.3)b4.5 (2.8)20.0 (12.3)c1.0 (0.6)Week 14-17 2020117.377.0 (65.7) ↓10.8 (9.2)16.8 (14.3)3.3 (2.8)9.0 (7.7) ↑0.5 (0.4)Stage IIWeek 2-17 2018/2019114.937.0 (32.2)5.0 (4.3)20.8 (18.1)34.3 (29.8)15.4 (13.4)2.5 (2.2)Week 2-8 2020116.133.4 (28.8) ↓4.1 (3.6)18.4 (15.9)38.4 (33.1) ↑18.3 (15.7)3.4 (3.0)Week 9-11 2020118.735.7 (30.1)5.7 (4.8)19.0 (16.0)36.0 (30.3)20.0 (16.9)2.3 (2.0)Week 12-13 2020142.042.5 (29.9)5.5 (3.9)26.5 (18.7)30.0 (21.1) ↓36.0 (25.4)d1.5 (1.1)Week 14-17 202083.327.5 (33.0)5.5 (6.6)16.0 (19.2)16.8 (20.1) ↓14.5 (17.4)e3.0 (3.6)Stage IIIWeek 2-17 2018/201931.12.0 (6.3)0.5 (1.7)5.8 (18.5)16.0 (51.5)5.3 (17.0)1.6 (5.0)Week 2-8 202027.92.4 (8.7)0.6 (2.1)5.0 (17.9)14.3 (51.3)4.7 (16.9)0.9 (3.1)Week 9-11 202026.72.0 (7.5)0.3 (1.3)5.7 (21.3)12.7 (47.5)f5.7 (21.3)0.3 (1.3)Week 12-13 202038.52.0 (5.2)0.5 (1.3)7.5 (19.5)19.0 (49.4)8.5 (22.1)1.0 (2.6)Week 14-17 202020.81.5 (7.2)1.3 (6.0) ↑4.5 (21.7)8.0 (38.6)4.5 (21.7)1.0 (4.8)Stage IVWeek 2-17 2018/201915.00.3 (2.3)0.0 (0.2)0.6 (4.0)5.3 (34.9)6.8 (44.9)2.1 (13.7)Week 2-8 202014.60.6 (3.9)0.0 (0.0)0.4 (2.9)4.7 (32.4)6.7 (46.1)2.1 (14.7)Week 9-11 202012.00.0 (0.0)0.0 (0.0)0.0 (0.0)3.3 (27.8)7.0 (58.3)1.3 (11.1)Week 12-13 202019.51.5 (7.7)0.0 (0.0)2.5 (12.8) ↑6.0 (30.8)7.5 (38.5)2.0 (10.3)Week 14-17 202013.80.3 (1.8)g0.0 (0.0)0.3 (1.8)3.8 (27.3)8.3 (60.0) ↑1.3 (9.1)

Citation Format: Anouk H Eijkelboom, Linda de Munck, Marie-Jeanne Vrancken Peeters, Marjolein Smidt, Mireille Broeders, Monique Bos, Marjanka K Schmidt, Maud Bessems, Luc Strobbe, Desirée van den Bongard, Aafke Honkoop, Janneke Verloop, Cristina Guerrero Paez, Marc Lobbes, Sabine Linn, Pieter Westenend, Catharina W Menke-van der Houven van Oordt, Jelle Wesseling, Vivianne Tjan Heijnen, Sabine Siesling, On behalve of the NABON COVID-19 consortium. Effect of the COVID-19 pandemic on the initial treatment of breast cancer in the Netherlands: A population-based study [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS7-88.