Abstract Studies have shown that local recurrences typically occur near the site of the primary cancer. Additionally, interest in personalized radiotherapy after breast conserving surgery (BCS) continues to grow, with de-escalation or omission pursued when oncologically appropriate. Based on current guidelines, wider margins, among other factors, can influence recommendations for de-escalation or omission. Completed trials of pegulicianine fluorescence guided surgery (pFGS) for real time residual cancer assessment within the lumpectomy during BCS showed removal of additional tumor and reduction of second surgeries compared with standard lumpectomy surgery. Specifically, in one study, pFGS guided the removal of residual cancer in 27 of 357 (7.6%) patients undergoing BCS. These previous trials enrolled a diverse cohort, including patients with invasive ductal carcinoma, invasive lobular carcinoma, and/or ductal carcinoma in situ (DCIS), with receptor profiles (HER2, ER, PR) reflective of the broader population receiving lumpectomies for breast cancer. We hypothesize that removal of residual cancer not identified during the initial BCS will reduce 5-year local recurrence rates and that pFGS-guided excisions will provide appropriate margin gains or remove residual disease, altering radiotherapy planning. 5-year follow-up data on patient outcomes and information about the adjuvant radiotherapy patients received following pFGS-guided excisions is needed to evaluate the impact of pFGS on local recurrence rates and on radiotherapy treatment decisions. Follow-up data will be collected from patients in prior prospective feasibility and pivotal studies to assess whether removal of residual cancer impacts local recurrence rates and radiotherapy treatments. Retrospective data collection from up to 640 breast cancer patients previously enrolled in parent trials NCT03686215 and NCT03321929 will be collected and analyzed, with a goal of demonstrating the long-term benefits of pFGS in improving surgical outcomes and informing radiotherapy decisions. Data collection will be conducted through systematic retrospective chart reviews, with rigorous quality control measures to ensure accuracy and reliability. A breast cancer radiation oncologist will determine the recommended radiotherapy treatment prior to pFGS use. The actual radiotherapy received following pFGS guided excisions will then be compared with these recommendations. Finally, radiotherapy treatments in the pFGS population will be compared with data drawn from contemporaneous publications. Data on cancer recurrence and survival will be collected. For each study participant that has developed a recurrent cancer, an evaluation of the location of the recurrent cancer compared to the index cancer will be performed. The 5-year median local recurrence rates and the 95% confidence interval (CI) will be calculated using Kaplan-Meier methods for time to event endpoints. Each patient’s follow-up period will be the time from index lumpectomy to last healthcare provider encounter. Local recurrence rates from these patients will be compared with rates reported in recent peer-reviewed literature. Citation Format: K. Smith, J. Ferrer, B. Schlossberg, S. F. Shaitelman, G. Doros, B. L. Smith. Impact of pegulicianine on radiotherapy decisions and long-term outcomes in patients undergoing breast conserving surgery abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS5-07-13.
Smith et al. (Tue,) studied this question.