Annelotte van Bommel

46 PATIENTS AND METHODS Data source Demographic and clinicopathological patient characteristics (age, histological subtype, grade, tumor–node– metastasis (TNM) classification) together with comprehensive multidisciplinary treatment information (surgical and medical adjuvant and neo-adjuvant therapy) were collected prospectively for all newly diagnosed Dutch patients with breast cancer in the NABON Breast Cancer Audit (NBCA) since 2011. 4 Registration was done by registrars of the Netherlands Cancer Registry and personnel of the individual hospitals. Patients receiving primary systemic treatment without subsequent surgical treatment were not registered in the NBCA. All female patients with primary invasive breast cancer without distant metastases diagnosed between January 1, 2011 and December 31, 2015 were extracted from the NBCA. Categories/Definitions The surgical procedure was categorized as BCS or mastectomy as determined by the final operative procedure for the primary tumor. Patients who underwent BCS with subsequent mastectomy as a second or third operative procedure were categorized as having had a mastectomy. Patients who had undergone a mastectomy were subdivided by receipt of IBR. Of patients who had undergone BCS, those who had received NAC were identified and categorized as such. The endpoint of interest was BCPP, which was the final outcome of local treatment obtained by one of the following treatment strategies: (1) primary BCS, (2) BCS after NAC, and (3) mastectomy followed by IBR. The remaining patients underwent a mastectomy either primary or following NAC. Analysis Descriptive statistics were used to describe the baseline characteristics of the study population. The proportions of patients who had undergone primary BCS were addressed for the study period of 5 years, and the effect of age on the rate of primary BCS was evaluated, as well as the variation in these proportions between individual hospitals. Similarly, the proportions within the categories that