Summary This metadata record provides details of the data supporting the claims of the related manuscript: “Clinical behavior and outcomes of breast cancer in young women with germline BRCA pathogenic variants”. The related study aimed to determine the impact of type of gene (BRCA1 vs. BRCA2) and hormone receptor status (positive [HR+] vs. negative [HR-]) on clinical behaviour and outcomes of mBRCA (germline BRCA pathogenic variant) breast cancer. Type of data: international, multicenter, hospital-based, retrospective cohort study. Subject of data: homo sapiens: young breast cancer (BC) patients carrying a germline BRCA pathogenic variant (mBRCA). Sample size: 1236. Population characteristics: women diagnosed at age ≤ 40 years with invasive early breast cancer (stage I-III) between January 2000 and December 2012. All included patients had a known germline BRCA1 or BRCA2 pathogenic variant. Data access The data generated and analysed during the related study are stored in the following four Excel spreadsheets: ‘Patient survival data.xlsx’, ‘Patient baseline, tumor and treatment data.xlsx’, ‘Patient risk reducing surgery data.xlsx’, ‘Patient eligibility criteria and survival data.xlsx’. These data are not publicly available for the following reason: data contain information that could compromise research participant privacy. However, the data can be made available upon reasonable request to the corresponding author. A list of which data file underlies which figure, table and supplementary table in the related manuscript is provided in the file ‘Lambertini et al underlying data lookup.csv’, included as part of this metadata record. The dataset analysed during this study is described with more details in the following manuscript: https://doi.org/10.1200/JCO.19.02399. Corresponding author(s) for this study Matteo Lambertini, MD PhD, IRCCS Ospedale Policlinico San Martino, University of Genova, Largo Rosanna Benzi 10, 16132 – Genova (Italy), Telephone +39 010 555 4254 – Fax: +39 010 555 6536. E-mail: [email protected].
Study approval The Institut Jules Bordet (Brussels, Belgium) coordinated the study and acted as central ethics committee. Ethics approval by the Institutional Review Boards of participating centers and patients’ written informed consent were obtained before inclusion whenever requested by local regulations.

Summary This metadata record provides details of the data supporting the claims of the related manuscript: “Clinical behavior and outcomes of breast cancer in young women with germline BRCA pathogenic variants”. The related study aimed to determine the impact of type of gene (BRCA1 vs. BRCA2) and hormone receptor status (positive [HR+] vs. negative [HR-]) on clinical behaviour and outcomes of mBRCA (germline BRCA pathogenic variant) breast cancer. Type of data: international, multicenter, hospital-based, retrospective cohort study. Subject of data: homo sapiens: young breast cancer (BC) patients carrying a germline BRCA pathogenic variant (mBRCA). Sample size: 1236. Population characteristics: women diagnosed at age ≤ 40 years with invasive early breast cancer (stage I-III) between January 2000 and December 2012. All included patients had a known germline BRCA1 or BRCA2 pathogenic variant. Data access The data generated and analysed during the related study are stored in the following four Excel spreadsheets: ‘Patient survival data.xlsx’, ‘Patient baseline, tumor and treatment data.xlsx’, ‘Patient risk reducing surgery data.xlsx’, ‘Patient eligibility criteria and survival data.xlsx’. These data are not publicly available for the following reason: data contain information that could compromise research participant privacy. However, the data can be made available upon reasonable request to the corresponding author. A list of which data file underlies which figure, table and supplementary table in the related manuscript is provided in the file ‘Lambertini et al underlying data lookup.csv’, included as part of this metadata record. The dataset analysed during this study is described with more details in the following manuscript: https://doi.org/10.1200/JCO.19.02399. Corresponding author(s) for this study Matteo Lambertini, MD PhD, IRCCS Ospedale Policlinico San Martino, University of Genova, Largo Rosanna Benzi 10, 16132 – Genova (Italy), Telephone +39 010 555 4254 – Fax: +39 010 555 6536. E-mail: [email protected].
Study approval The Institut Jules Bordet (Brussels, Belgium) coordinated the study and acted as central ethics committee. Ethics approval by the Institutional Review Boards of participating centers and patients’ written informed consent were obtained before inclusion whenever requested by local regulations.