Abstract Background: The National Accreditation Program for Breast Centers (NAPBC), in a 2014 statement of standards, endorsed breast conservation surgery (BCS) for women with AJCC stage 0,I, or II breast cancer, with a target of 50% BCS. Women comprise the fastest growing segment of Veteran's Health Administration (VA) enrollees, and have high rates of trauma exposure including military sexual trauma (MST). The VA conducts universal screening of all Veterans for MST. Implications for medical care, e.g. an increased rate of hysterectomy among survivors of MST, have been reported. While the numbers of breast cancers treated in VA are relatively small compared to non-VA centers, a trend toward decreasing rates of BCS in VA from 2000-2006 has been reported. Reasons for declining rates of BCS within VA, and the lower rates of BCS in the VA compared to the private sector remain unclear. The objective of this study was to identify determinants of mastectomy versus BCS in women Veterans with early stage breast cancer and to examine whether history of MST was associated with choice of mastectomy versus BCS. Methods: As a quality improvement study, we conducted a retrospective review of all early-stage (0,I,II) female breast cancer patients identified in the tumor registry between 2006-2015 at one Northeastern VA to determine rates of mastectomy and BCS. Through chart review, we examined potential determinants of BCS including age, stage, distance from treating VA facility, genetic testing, contralateral prophylactic mastectomy, and reconstructive surgery. History of MST was documented through chart review. Analyses were performed using unpaired t-test for age and distance from treatment facility and Fisher's exact test for significance comparing history of MST between surgical groups. Results: 70 women with early stage breast cancer were eligible for BCS. Of these, 39 underwent BCS and 31 underwent mastectomy (55% rate of BCS). Age and distance to treating VA were not significant. Women who underwent mastectomy were on average younger (p=0.21) and lived farther away (p =0.42) and were more likely to undergo genetic testing. Of the women who underwent genetic testing (10/70), none had mutations. The biggest difference seen between surgical groups was in history of MST, with women in the mastectomy group having more than twice the prevalence of MST, 58%, vs 31% in the BCS group (p = 0.0154 ). Patient characteristics by type of surgery performed BCS N=39Mastectomy n=31Age (mean)63.559.3Distance from VA56.7 miles67.7 milesGenetic testing (no mutations found)4 (10%)6 (19%)Reconstructive surgery05Prophylactic contralateral mastectomy011MST11(28%)18(58%) Conclusion: These data suggest that MST is associated with choice of mastectomy over BCS. MST results in poor body image which may impact decisions about breast surgery. Trauma-informed strategies for counseling women about options for surgical management of early stage breast cancer may be needed to ensure that women with MST and other forms of trauma pursue evidence-based cancer treatment. Further work with a larger cohort is needed to better understand these findings. Citation Format: Oshry LJ, Naomi K, Megan GR. Military sexual trauma is associated with an increased prevalence of mastectomy versus breast conserving surgery in a population of female veterans with early stage breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-15-01.