INTRODUCTION Breast reconstruction surgery is an integral part of breast cancer treatment that aims to restore breast appearance after mastectomy. We assessed breast symmetry following breast reconstruction using measures of distance and volume. MATERIAL AND METHODS Patients undergoing breast reconstruction surgery were enrolled in an IRB approved study from 2011 to 2014 at The University of Texas MD Anderson Cancer Center. We utilized pre- and post-operative 3D surface images (3dMDtorso, 3dMD LLC, Atlanta, GA) from 53 women who had completed the breast reconstruction process (83% at 18 months (M), 9.4% at 12M and 7.6% at 9M). Patients provided approved consent. Thirty-six women had bilateral and 17 had unilateral surgery. Eleven patients in the unilateral group had symmetry surgery on the contralateral breast (5 had mastopexy, 4 had reduction, 1 had augmentation, and 1 had augmentation and mastopexy). Within the bilateral group, 9 patients underwent autologous reconstruction, 21 received implants, and 6 had mixed (autologous and implant) procedures. Within the unilateral group, there were 10 implant and 7 autologous reconstructions. We measured the sternal notch (SN) to lowest visible point (LVP) distance and volume for each breast. Breast symmetry was assessed using 1) Difference between the left and right breasts for the SN-LVP distance and volume measures, 2) SN-LVP distance ratio and volume ratio computed using values for the left and right breast. The smaller value was divided by the larger, so that a ratio of 1.0 indicated perfect symmetry [1]. Differences < 5 mm for SN-LVP distance and < 50 cc for breast volume were used as indicators of symmetry [1]. RESULTS Overall, pre-operatively 50.9% patients showed a SN-LVP difference < 5 mm compared to 35.9% post-operatively, whereas 43.4% showed a breast volume difference < 50 cc pre-operatively compared to 62.3% post-operatively. Mean pre- and post-operative SN-LVP distance ratios were found to be 0.97 ± 0.03 and 0.96 ± 0.03, respectively, whereas the breast volume ratios were 0.91 ± 0.06 and 0.92 ± 0.08, respectively. Shapiro‐Wilk tests showed non‐normal distribution for both ratios; thus, non‐parametric analysis was performed using Mann-Whitney U-test and, for matched pairs, the Wilcoxon Matched Pairs Sign-Ranked test. For both distance and volume ratios, we failed to reject the null hypothesis that the median of the paired differences between the pre- and post-operative values was zero. Also, no significant differences were found for both ratios when comparing autologous and implant-based surgeries. Bilateral reconstructions were compared to unilateral procedures that included a contralateral symmetry procedure. Significantly higher distance ratios (0.97 ± 0.03, median of 0.98, p = 0.005) were found for bilateral reconstructions compared to unilateral (0.94 ± 0.04, median of 0.94), but no differences in volume ratios were noted. Significant differences were noted for both distance (p = 0.033) and volume (p = 0.009) ratios when comparing bilateral (distance: 0.96 ± 0.02, median of 0.97 and volume: 0.96 ± 0.03, median of 0.97) to unilateral implant-based reconstructions (distance: 0.93 ± 0.04, median of 0.94 and volume: 0.91 ± 0.05, median of 0.90), but no difference in symmetry was found between unilateral and bilateral autologous reconstructions. CONCLUSION Distance symmetry was noted in a higher percentage of the pre-operative population compared to post-operative, whereas a larger proportion of the post-operative patients showed volume symmetry compared to the pre-operative group. Implant-based bilateral procedures showed improved symmetry compared to the unilateral procedures. REFERENCES 1.Cheong AL, Liu J, Reece GP, Nicklaus KM, Bordes MC, Hanson SE, Markey MK, Merchant, FA “Natural Breast Symmetry in Preoperative Breast Cancer Patients”, Plastic and Reconstructive Surgery - Global Open: 2019;7(7):e2297. Citation Format: Thao Bui, Urmila Sampathkumar, Zhale Nowroozilarki, Jun Liu, Mary Catherine Borders, Summer E Hanson, Gregory P Reece, Mia K Markey, Fatima A Merchant. Symmetry of breasts following reconstructive surgery [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 PS1-24.