Abstract PD15-04: PD15-04 Overall survival following breast conserving surgery and adjuvant radiotherapy compared with mastectomy for early stage breast cancer: a systematic review and meta-analysis
Authors: Rajan Kiran Kasper , Fairhurst Katherine , Birkbeck Beth , Wilson Rebecca , savovic Jelena , Holcombe Chris , Potter Shelley 
Published: March 2023

Abstract
Background Breast conserving surgery with adjuvant radiotherapy (BCS+RT) and mastectomy are currently offered as oncologically equivalent options for the surgical management of early breast cancer based on findings from randomised controlled trials (RCTs) conducted over four decades ago. Since then, locoregional and systemic breast cancer treatments have improved significantly and several recent observational studies suggest a survival advantage in patients receiving BCS+RT compared to those having mastectomy. If BCS+RT is oncologically superior to mastectomy, this may dramatically impact surgical treatment recommendations. The aim of this systematic review was to identify, critically appraise and summarise the contemporary literature comparing survival following BCS+RT and mastectomy to inform surgical decision-making for patients with early breast cancer. Methods A systemic search of MEDLINE, Cochrane Central Register of Controlled Trials and Embase identified studies published between 1st January 2000 to 22nd September 2021. Included were primary research studies published in English comparing overall survival in women undergoing primary surgery with either BCS+RT or mastectomy for unilateral stage I to III breast cancer. Excluded were studies evaluating neoadjuvant chemotherapy; rare breast cancer subtypes (e.g. mucinous) or in specific patient populations (e.g. pregnancy associated breast cancer) and those that completed recruitment before 1st January 1990. We used the ROBINS-I tool to assess the risk of bias in study results and GRADE to assess the overall certainty of evidence. All papers without critical risk of bias were included in a quantitative meta-analysis. Where more than one study reported outcomes in overlapping population-based registry cohorts, the study with the most recent data on the largest cohort was selected for analysis. The primary analysis was a random effects meta-analysis with a fixed effect model undertaken as sensitivity analysis. A secondary meta-analysis was performed for studies only including triple negative breast cancers. All analyses were conducted using STATA17. Results 10,876 abstracts were screened and 157 full-text papers assessed for eligibility, of which 93 (17 multi-centre observational studies, 30 were single-centre observational studies and 46 registry-based studies) met the inclusion criteria for the review. 25 papers were excluded from meta-analysis due to an overall critical risk of confounder bias and 27 were excluded due overlapping study populations. 36 studies (34 with serious risk of bias and 2 with moderate risk of bias) reporting survival outcomes on 1,321,291 patients (729,789 undergoing BCS+RT and 591,502 undergoing mastectomy) were included in the meta-analysis. The pooled hazard ratio was 0.72 (95% CI 0.64– 0.81, p&lt; 0.001, I2 97.6%) demonstrating improved overall survival for patients undergoing BCS+RT compared with those receiving mastectomy. The sensitivity analysis, using a fixed effect model, showed a hazard ratio of 0.88 (95% CI 0.87 – 0.89, p&lt; 0.001, I2 97.6%) for survival in women undergoing BCS+RT compared with mastectomy. Meta-analysis of 8 studies reporting survival in 17,181 patients with triple negative breast cancer showed a hazard ratio of 0.73 (95% CI 0.68 – 0.79), p&lt; 0.001, I2 34.7%) for those receiving BCS+RT versus mastectomy. Discussion This meta-analysis provides further, albeit very low certainty evidence, that overall survival is improved following BCS+RT compared with mastectomy in a contemporary cohort of patients treated for early-stage breast cancer. These results should be interpreted with caution due to the heterogeneity of included studies and the high risk of bias associated with observational data. As future RCTs will not be feasible, well-designed large-scale prospective observational studies are needed to provide better evidence to support surgical decision-making in early-stage breast cancer.
Citation Format: Kiran Kasper Rajan, Katherine Fairhurst, Beth Birkbeck, Rebecca Wilson, Jelena savovic, Chris Holcombe, Shelley Potter. PD15-04 Overall survival following breast conserving surgery and adjuvant radiotherapy compared with mastectomy for early stage breast cancer: a systematic review and meta-analysis [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD15-04.