Data and metadata supporting the published article: Contralateral breast cancer risk in patients with ductal carcinoma in situ and invasive breast cancer

In this study, the authors aimed to assess contralateral breast cancer (CBC) risk in patients with ductal carcinoma <i>in situ</i> (DCIS) compared to invasive breast cancer (BC).<br> <b>Data access: </b>The datasets generated and/or analysed during the current study are not publicly available, as the study has used external data from the Netherlands Cancer Registry. The datasets will be made available from the Netherlands Cancer Registry upon reasonable request (data request study number K18.245). To apply for data access, please visit https://www.iknl.nl/en/ncr/apply-for-data. The datasets that support figures 1 and 2, and supplementary figures 2-4, are publicly available in the figshare repository, as part of this data record.<br> <b>Study approval: </b>The NCR Privacy Review Board approved the proposal. Data were handled in accordance with privacy regulations for medical research.<br> <b>Study aims and methodology: </b>Contralateral breast cancer (CBC) is the most frequent second cancer reported after first invasive breast cancer (BC). The cumulative incidence of invasive CBC for women following invasive BC is ~0.4% per year. Several studies have shown a decrease in CBC incidence as a result of (neo)adjuvant systemic therapies. The aim of this study was to assess the risk of developing invasive CBC in DCIS patients in direct comparison with patients diagnosed with invasive BC using a large population-based cohort of Dutch BC patients, taking age, mode of first BC detection, and (neo)adjuvant systemic therapy into account. In addition, the authors evaluated the CBC risk prediction performance in patients diagnosed with DCIS. Women diagnosed with DCIS (N=28,003) or stage I-III BC (N=275,836) between 1989-2017 were identified from the nationwide Netherlands Cancer Registry. Cumulative incidences were estimated, accounting for competing risks, and hazard ratios (HRs) for metachronous invasive CBC. To evaluate effects of adjuvant systemic therapy and screening, separate analyses were performed for stage I BC without adjuvant systemic therapy and by mode of first BC detection. Multivariable models including clinico-pathological and treatment data were created to assess CBC risk prediction performance in DCIS patients. For more details on the methodology, please read the related article.<br> <b>Data supporting the figures, tables, and supplementary files in the article: </b>Dataset<b> </b><b>NKR_K18.245.txt</b>, is in text file format, and supports the findings of this study. This file will be made available upon reasonable request, as described in the data access section above. The following datasets are in Excel file format, support figures 1 and 2, and supplementary figures 2-4, respectively, and are part of this figshare data record: <b>Underlying data_Figure 1.xlsx</b>, <b>Underlying data_Figure 2.xlsx</b>, <b>Underlying data_Supplementary Figure 1.xlsx</b>, <b>Underlying data_Supplementary Figure 2.xlsx</b> and <b>Underlying data_Supplementary Figure 3.xlsx</b>. The aforementioned Excel files show the underlying data points of the cumulative incidence figures provided in the article.