Supplementary Material for: Impact of Oncoplastic Breast Surgery on Rate of Complications, Time to Adjuvant Treatment, and Risk of Recurrence

<b><i>Background:</i></b> The aim of this study was to compare the risk of complications and recurrence between oncoplastic and conventional breast surgery. <b><i>Methods:</i></b> This is a retrospective analysis of a consecutive series of 436 patients with stage I–III breast cancer who underwent surgery at the University Hospital of Basel between 2011 and 2018. <b><i>Results:</i></b> The nipple/skin-sparing mastectomy (NSM/SSM) group showed significantly more delayed wound healing (32.7 vs. 5.8%, <i>p</i> &lt; 0.001) and skin necrosis (13.9 vs. 1.9%, <i>p</i> = 0.020) compared to conventional mastectomy (CM), which corresponded to significantly higher odds of short-term complications (OR 2.34, 95% CI 1.02–5.35, <i>p</i> = 0.044). The incidence rate of long-term morbidity in oncoplastic breast-conserving surgery (OBCS) was significantly higher compared to conventional breast-conserving surgery (CBCS; 25.5 vs. 11.3 per 100 patient years [PY], <i>p</i> &lt; 0.001), in particular concerning chronic pain (13.3 vs. 6.6, <i>p</i> = 0.011) and lymphedema (4.1 vs. 0.4, <i>p</i> = 0.003). Seroma as a long-term morbidity occurred more often in the CM group compared to the NSM/SSM group (5.8 vs. 0.5 per 100 PY, <i>p</i> = 0.004). Patients received adjuvant treatment earlier after CM compared to NSM/SSM (HR 1.83, 95% CI 1.05–3.19, <i>p</i> = 0.034). There were no significant differences in the incidence of positive margins nor in the odds of recurrence after OBCS versus CBCS and after NSM/SSM versus CM. <b><i>Conclusions:</i></b> Even though the present study confirmed expected differences in complications and morbidity, it suggested that oncoplastic surgery is oncologically safe. Patients undergoing NSM/SSM should be followed closely to allow early detection and treatment of frequently associated complications and ensure timely start of adjuvant therapy.