Abstract PS1-17: Comparing survival differences between breast-conserving therapy and mastectomy in patients with early-stage breast cancer undergoing upfront surgery
Authors: Yi Min , Gregor Mariana Chavez Mac , Smith Benjamin , Caudle Abigail S , DeSnyder Sarah M , Kuerer Henry M , Hunt Kelly K 
Published: February 2021

Abstract
Background: Over the last decade, patients with early-stage breast cancer have been undergoing total mastectomy (TM) with increasing frequency. Our center reported that local recurrence rates with breast conserving therapy (BCT) declined throughout the 27-year period: from 7.1% for patients treated during 1970–1984 to 1.3% for patients treated during 1994–1996. More recently, several groups have published slightly improved survival rates in patients undergoing BCT compared with TM. The aim of this study was to evaluate trends in TM rates and compare overall survival (OS), distant metastasis-free survival (DMFS), local-regional recurrence (LRR) and disease-specific survival (DSS) between BCT and TM in patients with early-stage breast cancer undergoing upfront surgery. Methods: We identified women with clinical stage T1–2, N0–1, M0 breast cancer who underwent surgery as first treatment modality from 1/1/2000 to 12/31/2014 at our center. TM rates and survival outcomes were evaluated. Because the decision for surgery for those patients was not random, differences in patient, tumor and treatment characteristics with respect to surgery types were adjusted using inverse probability weighting (IPW) based on propensity scores. Variables in the model included age at diagnosis, clinical tumor T category, clinical nodal category, estrogen receptor (ER), human epidermal growth factor receptor 2 (HER2) status and year of surgery, and a multinomial logit model was used for surgery treatment assignment and a Gamma model was used for the time to censor. IPW models were used to adjust for impact of surgery types on survival outcomes. Similar analysis was used in 6 subsets: Stage I & hormone receptor (HR)+/HER2-, Stage I & HER2+, Stage I &triple negative breast cancer (TNBC), Stage II & HR+/HER2-, Stage II & HER2+, Stage II & TNBC. Patients undergoing TM with RT were excluded from subset analysis due to small sample size.
Results: A total of 8,256 patients were included, of them, 4701 (56.9%) underwent BCT, 2862 (34.7%) underwent TM without RT and 693 (8.4%) underwent TM+RT. Patients who underwent TM were younger and were more likely to have larger tumors, positive lymph nodes, higher grade, and HER2-positive tumors. TM rates increased in patients &lt;=50 years old from 2006-2013. At a median follow-up time of 6.1 years, multivariable Cox model showed that patients who underwent BCT had improved OS (HR: 0.8,95%CI: 0.7-0.99, P=0.02) and had a similar DSS, DMFS, and LRR compared to patients who underwent TM without RT. After IPW adjusting, patients undergoing BCT had a slightly worse DSS (RR: 1.2, 95%CI: 1.02-1.4, P=0.03) and similar OS, DMFS and LRR compared to patients underwent TM without RT in the whole cohort. In subset analyses, after IPW adjusting, there were no survival differences in OS, DSS, and DMFS between TM without RT and BCT. Patients with TNBC undergoing BCT had a lower LRR compared to TM (RR: 0.4, 95% CI: 0.3-0.6, P&lt;0.001) regardless of clinical stage. Conclusions: In whole cohort, after IPW adjusting, patients undergoing BCT had a slightly worse DSS compared to patients underwent TM without RT, and those differences in DSS have disappeared in the subset analysis. LRR was lower in patients with TNBC breast cancer undergoing BCT although there as a similar OS, DSS and DMFS compared with TM in subset analysis. These contemporary data may help physicians in surgical decision making for patients who are candidates for either TM or BCT.
Table 1. Results from multivariable Cox models for factors associated with survival outcomes and IPW adjusted models for factors associated with survival outcomesCox ModelIPW adjusting modelsFactorsHRP95%CIRRP95% CIOSSurgery typeTM without RTBCT0.80.020.70.991.01.00.9-1.1TM with RT1.00.960.81.31.10.60.9-1.3DSSSurgery typeTM without RTRefBCT1.10.40.81.51.20.031.02-1.4TM with RT1.70.0051.22.61.30.021.04-1.6DMFSSurgery typeTM without RTRefBCT1.10.40.91.41.00.50.9-1.2TM with RT1.70.0021.22.40.90.70.7-1.2 LRRSurgery typeTM without RTRefBCT1.30.11.01.71.00.70.7-1.2TM with RT0.40.020.20.90.80.10.6-1.1Subsets IPW adjusted models for factors associated with LRRBCT vs. TM without RTStage I & HR+/HER2-No. of patientsTM without RT/BCTRRP95% CIStage I & HER2+1469/29451.00.90.8-1.3Stage I & TNBC199/2850.70.30.3-1.5Stage II & HR+/HER2-128/3170.4&lt;0.0010.3-0.6Stage II & HER2+690/7451.10.70.7-1.8Stage II & TNBC102/1080.90.50.5-1.4Stage I & HR+/HER2-110/1570.50.0480.3-0.99HER2 – human epidermal growth factor receptor 2; HR – hormone receptor; TNBC – triple negative breast cancer
Citation Format: Min Yi, Mariana Chavez Mac Gregor, Benjamin Smith, Abigail S Caudle, Sarah M DeSnyder, Henry M Kuerer, Kelly K Hunt. Comparing survival differences between breast-conserving therapy and mastectomy in patients with early-stage breast cancer undergoing upfront 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 PS1-17.