Abstract Introduction: Skin and Nipple Sparing mastectomies are an alternative for patients not eligible for conservative breast surgery, allowing for better aesthetic results than classical mastectomies. We aimed to evaluate oncological safety outcomes and identify risk factors for locoregional recurrence in patients submetided to sparing mastectomies. Methods: A retrospective analysis was conducted on all consecutive cases of skin sparing mastectomy (SSM) or nipple sparing mastectomy (NSM) for a primary diagnosis of invasive or in situ breast carcinoma, treated at an oncologic center, from january 2013 to may 2019. Primary outcome was locoregional recurrence. Secondary outcomes included overall survival and disease-free survival, median time to recurrence and median follow-up time. Risk factors for locoregional recurrence were analysed using chi-square test and t test where suitable, followed by a logistic regression model. Survival analysis was performed using Kaplan-Meier curve. Results: We included 461 cases; 59 cases (13%) presented with carcinoma in situ and 402 (87%) with invasive carcinoma. Median age was 46 (24-78) years. Seventy-one (15%) patients had locally advanced disease. SSM were performed in 226 (49%) cases and NSM in 235 (51%). Neoadjuvant chemotherapy was administered in 141 (31%) cases and adjuvant radiotherapy in 203 (44%). Locoregional recurrence rate was 3,4% with no nipple-areolar complex (NAC) recurrence. Median time to recurrence was 22 (1-54) months. Overall survival was 91,7% and disease-free survival was 80,4% at a median follow-up time of 39 (1-86) months.Factors associated with locoregional recurrence in univariate analysis were tumor size over 4cm, high histological grade, negative endocrine receptors, neoadjuvant chemotherapy and absence of endocrine therapy (p<0,05), however none of these factors were independently associated with recurrence as ascertained by logistic regression model. There was no association of recurrence with familial risk mutation. Conclusions: SSM and NSM present as a safe surgical approach to breast cancer requiring mastectomy, with a locoregional recurrence rate comparable to classical mastectomy. It was not identified a group of patients who are at risk of recurrence. Nonetheless, risk factors such as tumor size, histological grade, absence of endocrine receptors, neoadjuvant chemotherapy and absence of endocrine therapy may correlate with less favorable outcomes. Citation Format: Beatriz Costeira, Francisca Brito da Silva, Rodrigo Oom, Cristina Costa, João Vargas Moniz, Rui Serra Alves, Nuno Abecasis, Catarina Rodrigues Santos. Skin and nipple sparing mastectomies - oncologic outcomes from an oncologic center [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS1-59.