Background: Recent medical literature reports that mastectomy rates are increasing in early breast cancer. The reasons for this have not yet been elucidated and appear to be complex and can be related to: availability of immediate reconstruction, expertise of the surgeon, increment of genetic tests and beliefs, unwillingness or impossibility of receipting radiotherapy, and information of the patients themselves. The present study aimed to demonstrate mastectomy rates throughout the years from a single Brazilian institution and to correlate it with age, neoadjuvant therapies and tumor staging. Methods: A retrospective analysis of breast cancer surgeries from patients treated at Hospital Sírio-Libanês cancer center from 2005 to 2018 was performed. The institutional database electronically of physically registered in this period included pathology, radiology, and clinical information. Chi-squared coefficient of correlation was applied for categorical variables analysis of association, and for significant findings a multivariate regression analysis was performed. All statistical analyses were performed in STATA version 15.1C. Results: Medical records from 2,942 patients treated were analyzed. 1,798 mastectomies (including nipple-sparing mastectomies and skin-sparing mastectomies) were performed against 1,144 conservative surgeries (61.11% x 38.89%). The range of mastectomy rates varied from 73.04% (2007) to 48.8% (2018) and mastectomy rates showed a slight decrease (53.84% in 2005 and 48.14% in 2018). Type of surgery (conservative, mastectomy, skin-sparing mastectomy) was associated with neoadjuvant treatment (p<0.001). Multiple regression analysis found that radical surgery was inversely correlated to the date of surgery, having radical strategies fewer indications along with the time (R < -0.001 ; t= -2.15 ; p=0.03), inversely correlated to age, being older aged patients more likely to underwent radical strategies (R= -0.004 ; t= -4.74 ; p<0.001), directly correlated to advanced stages (R=0.13 ; t=10 ; p<0.001). No significant linear correlation was found between type of surgery and neoadjuvant treatment when controlled for date, age and T staging. Conclusions: These results demonstrate that our mastectomy rates, differently from global trends, did not increase through the past 15 years. These findings are probably related to impossibility of genetic tests in this population, accurate diagnostic techniques and the achievement of higher response rates with neoadjuvant treatment. Interestingly, breast-conserving surgery rates were inversely correlated with older age, which can reflect an individualized therapeutic approach among a subgroup of patients potentially vulnerable to chemo-related toxicity. Citation Format: Thatyane EspósitoGallo Cunha, Thamyse FernandaSá Dassie, Julianne MariaSilva Lima, Max Senna Mano, Lincon Jo Mori, Samir Abdallah Hanna, Sandro ViniciusMachado Melo, Gustavo Nader Marta, Felipe EduardoMartins Andrade. Mastectomy rates in a single Brazilian institution through the past 15 years: Are we following the global trend? [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P1-20-29.

e12595 Background: Preoperative breast MRI can provide important clinical information on the surgical management of BC patients (pts). However, there is no evidence that it can produce a statistical impact on surgical outcomes in the early BC setting. This retrospective study sought to evaluate whether preoperative MRI was significantly correlated with CSur among early BC pts. Methods: Digital and physical records from 532 pts treated in a specialized BC center in Brazil from 2005 to 2018 were analyzed. The institutional database registered pathological, radiological and clinical information. The categorical variables CSur and MRI were analyzed by Chi-squared coefficient of correlation, whereas significant correlations were included in a multivariate logistic regression model. All statistical analysis were performed in STATA version 15.1C. Results: The present analysis included 532 pts. The diagnosis was suspected through suspicious self-exam in 380 pts (71%), while 129 pts (24%) had altered mammary screening tests. Clinical T and N stages were: T0-1=154pts (29%); T2=179 pts (33%); T3=135 pts (25%); T4=49 pts (9%); N0=267 pts (50%); N1=172 pts (32%); N2=80 pts (15%). Neoadjuvant treatment was performed in 223 pts (42%). MRI was indicated in 248 pts (46%). CSur was performed in 149 pts (28%). Margins were positive in 15 cases. This study found a statistically significant correlation between CSur and MRI ( X2 = 8.07; p=0.018). Although, when controlled for neoadjuvant treatment, T, N, and age, the independent variable MRI was not a statistical predictor of CSur (R=0.008; t=0.25; p=0.8; 95%CI -0.57 – 0.74). Advanced T and neoadjuvant treatment were inversely correlated with CSur in the multivariate analysis (R= -0.11; t= -7.8; p<0.001 and R= -0.11; t= -2.88; p=0.004, respectively). One multivariate analysis to evaluate predictors of T stages showed that suspicious self-exam and N stage had a significant linear relationship with T stages when controlled for age (R=0.70; t=7.9; p<0.001; and R=0.76; t=15; p<0.001, respectively). Conclusions: Preoperative MRI can have impact on the conservative surgical management of curable BC patients and the present analysis showed a positive correlation. In the logistic regression model, MRI was not identified as a predictor of CSur, however the proportion of locally advanced BC may have influenced the results. Further studies must be strengthened for identifying in which subgroup of patients MRI may be a predictor of surgical outcomes.