Abstract P2-08-20: Long-term outcomes after breast conserving surgery compared with mastectomy in early breast cancer in Korea
Authors: Kim Hakyoung , Ahn Sei Hyun , Son Byung Ho , Lee Jong Won , Chung Il Yong , Ko Beom Seok , Kim HeeJeong , Kim Jisun , Lee Young Ju , Shin Yungil , Choi Soojeong , Ryu Ho Hyun , Lee Sae Byul 
Published: March 2020

Abstract
Introduction: In some recent studies, breast conserving surgery (BCS) has been reported to improve survival rates compared with modified radical mastectomy (MRM) in early breast cancer.
The purpose of this study was to evaluate long term outcome of Korean women with early breast cancer and compare the recurrence rate and overall survival according to operation methods; BCS vs MRM.
Method: In this population-based study, we used information from two databases including the nationwide Korean Breast Cancer Registry (KBCR) and Asan Medical Center (AMC).
We identified patients from KBCR who were diagnosed breast cancer stage 1-3 between 1998-2012 and were given either BCS or MRM regardless of axillary staging or dissection or use of adjuvant systemic therapy. To minimize confounding bias caused by variables other than operation method, we used exact match pairing of variables such as age, tumor stage and subtypes except for adjuvant radiotherapy. We compared overall survival (OS) and cancer specific survival (CSS) of BCS group and MRM group. As KBCR is multi-centered and online based registry program, we used a single center database to validate the result of KBCR. We selected patients who were diagnosed with breast cancer stage 1-3 between 1998-2008 from AMC and divided them into BCS group and MRM group. We used exact match pairing of all variables except adjuvant radiotherapy in this cohort as well and compared OS, CSS and disease-free survival (DFS).
Result: Of 59121 patients who were selected from KBCR, 26581 patients received MRM and 32540 patients received BCS. 18989 patients in each group were remaining after exact match pairing. After exact matching to adjust variables other than operation method, BCS was significantly associated with better OS and CSS compared with MRM. After exact matching HR for OS and CSS were 1.47 [0.36-1.59 p&lt;0.001], 1.37 [1.20-1.57 p&lt;0.001] respectively.
Of 8710 patients who from AMC, 2490 patients were excluded as they had unknown variables we needed to know for exact matching. 3095 patients received MRM and 3125 patients received BCS. 1790 patients in each group were remaining after exact match pairing. In this cohort after exact BCS was also significantly associated with better OS, CSS and DFS compared with MRM. After exact matching HR for OS, CSS and DFS were 1.64 [1.30-2.06 p&lt;0.001], 1.71 [1.33-2.20, p&lt;0.001], 1.37 [1.14-1.64, p&lt;0.001] respectively. Median follow up was 88.6 month before matching and 89.2 month after matching.
Conclusion: When we adjusted confounding variables by exact matching BCS showed better overall and cancer specific survival and in AMC database better recurrence free survival compared to MRM in early breast cancer patients.
These results suggest that BCS is at least equivalent to mastectomy in terms of recurrence free survival and overall survival and may affect treatment decisions in early breast cancer patients.
Citation Format: Hakyoung Kim, Sei Hyun Ahn, Byung Ho Son, Jong Won Lee, Il Yong Chung, Beom Seok Ko, HeeJeong Kim, Jisun Kim, Young Ju Lee, Yungil Shin, Soojeong Choi, Ho Hyun Ryu, Sae Byul Lee. Long-term outcomes after breast conserving surgery compared with mastectomy in early breast cancer in Korea [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 P2-08-20.