Metadata supporting the published article: Guidelines for managing patients with primary ER+HER2- breast cancer deferred from surgery due to the COVID-19 pandemic.

In this study, the authors have collated data from multiple international trials of presurgical endocrine therapy in order to provide guidance on the identification of patients who may have insufficiently endocrine-sensitive tumors and should be prioritised for early surgery or neoadjuvant chemotherapy rather than neoadjuvant endocrine therapy (NeoET) during or in the aftermath of the COVID-19 pandemic for safety or when surgical activity needs to be prioritized.

Data access: The majority of the datasets supporting the findings of this study are derived from clinical trials that have not yet been published. Other datasets are yet to be published in association with trial secondary endpoints. For these reasons, the data supporting the findings of this study are not publicly available, but will be made available on reasonable request from the corresponding author, Professor Mitch Dowsett, email: mitchell.dowsett@icr.ac.uk. Datasets that relate to the Z1031 clinical trial will be made available to researchers on request, by contacting the ALLIANCE Operations office (email: concepts@allianceNCTN.org) and completing an Alliance Data Sharing Request Form (https://www.allianceforclinicaltrialsinoncology.org/main/cmsfile?cmsPath=/Public/Datasharing/files/Alliance data sharing request form.pdf).

Study approval and patient consent: All patients gave informed consent within each of the trials for the derivation of the data sourced for this study.

The POETIC case-control study was approved by the London-South East Research Ethics Committee. The PALLET trial was approved by the London-Fulham Research Ethics Committee. The IL1839/223 trial was approved by the Royal Marsden Hospital Ethics Committee. The ADAPT HR+/HER2 trial was approved by the University of Cologne Institutional Review Board. The Z1031and ALTERNATE trials were approved by the NCI Central Institutional Review Board.

Study aims and methodology: In many countries severely affected by the COVID-19 pandemic the surgical management of primary breast cancer is being confined to patients at highest risk for early disease progression. Thus, surgery for ER+ HER2- tumors (>70% of the overall breast cancer population) is being frequently deferred in favour of neoadjuvant endocrine therapy (NeoET) because of patient safety concerns and resource availability. The accurate identification of patients most likely to be poorly controlled by NeoET would allow their surgery or systemic treatment to be prioritised during or in the aftermath of COVID19 according to local circumstances. Conversely, identification of those likely to experience adequate tumor control by NeoET over a period of surgical deferment would be reassuring. The immediate objective of this study, was to review the published data that underpins the application of NeoET in more normal circumstances and to collate this information with previously unpublished data from many thousands of patients in ongoing studies to produce a simple algorithm for patient management.

These are the number of patients that participated in each trial: POETIC (n=339), PALLET (n=131), IL1839/223 (n= 176), ADAPT HR+/HER2 (n= 3 311), Z1031 (n= 214), ALTERNATE (n= 1299).

For details on immunohistochemical scoring (Ki67, estrogen receptor (ER) and progesterone receptor (PgR)) and data analyses, please read the related article.

Data supporting the findings of this study: Dataset names, formats and data access conditions are described in the data file Dowsett et al.xlsx.

Software needed to access data: The file Z1031B_ki67.sas requires the SAS statistical software to be accessed.