Abstract P2-12-03: Impact of the SSO-ASTRO consensus guidelines on invasive margins on the re-excision rate among patients undergoing breast conserving surgery (BCS)

Abstract

Abstract Background: BCS has been historically associated with a high re-excision rate, driven in part by lack of consensus on what constitutes an adequate negative margin. The SSO-ASTRO consensus guideline on invasive margins defined a negative margin as no ink on tumor based on evidence suggesting that more widely clear margins do not further decrease the risk of recurrence, potentially reducing the need for re-excision. In a large nationwide cohort of breast cancer patients undergoing BCS for invasive breast cancer we evaluate the rates of re-excision following BCS before and after the SSO-ASTRO consensus guidelines were disseminated. Methods: Breast cancer patients undergoing BCS for invasive breast cancer between January 2012 and December 2015 were identified among female beneficiaries in the MarketScan database. Patients receiving chemotherapy before surgery were excluded. Based upon presentation of the guideline recommendations in October 2013, the pre-guideline period was defined from January 2012 to September 2013. On-line publication of the guideline in February 2014 led to definition of the post-guideline period from March 2014 onwards. The peri-guideline period was defined as the time between the pre and post-guideline intervals. Any re-excision or mastectomy within 3 months of initial BCS was identified using ICD-9 or CPT codes. Overall re-excision rates and 95% CI were calculated; groups were compared using X2test. We used a regression model to evaluate the association between pre-peri-post guideline period and re-excision while adjusting for important covariates. Results are expressed as risk ratios (RRs) and 95%CI. Results: A total of 38,573 patients were included (20,159 in the pre-guideline, 4,607 peri-guideline and 13,807 post-guideline). The overall re-excision rate was 23.9% (95%CI 23.4-24.3). The pre-guideline re-excision rate was 25.3% (95%CI 24.7-29.9) compared to 21.6% (95%CI 20.9-22.3] in the post-guideline period. (p<0.001). The rate of mastectomy as the final surgical procedure was 20.2% in the pre-guideline period and 19.1% in the post-guideline (p=0.15). We observed significant geographic variability by state in the decrease of the re-excision rates. No change in re-excision rates was seen in Mississippi, Vermont, Georgia, Oregon, West Virginia, Arkansas, Oklahoma and Tennessee. An absolute decrease greater than 10% in the re-excision rate was observed in Indiana, Nebraska, Alabama, Maine and Nevada. In the multivariable analysis, patients undergoing BCS in the post-guideline period had a statistically significant decrease in the risk of re-excision compared to patients undergoing surgery in the pre-guideline period (RR=0.87; 95%CI 0.84-0.91; p<0.001). Conclusions: There has been a statistically significant decrease in the re-excision rate after BCS associated with the time of the dissemination of the SSO-ASTRO consensus guideline on invasive margins. The wide geographical variation observed suggests differences in the adoption rates. Our study confirms the impact that guidelines have modifying patterns of practice, reducing the frequency of unnecessary surgical interventions. Citation Format: Chavez-MacGregor M, Lei X, Morrow M, Giordano SH. Impact of the SSO-ASTRO consensus guidelines on invasive margins on the re-excision rate among patients undergoing breast conserving surgery (BCS) [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-12-03.