2954 - The Influence of Close Margins on Local Recurrence Rates after Partial Breast Irradiation (PBI)
Presenter(s)
A. Ionescu1, C. White2, Z. Zhang2, I. J. Choi3, D. A. Roth O’Brien1, M. B. Bernstein1, A. J. Xu3, J. J. Cuaron3, Q. LaPlant3, B. McCormick3, S. N. Powell3, L. Z. Braunstein1, and A. J. Khan1; 1Memorial Sloan Kettering Cancer Center, New York, NY, 2Department of Epidemiology and Biostatistics, Memorial Sloan Kettering Cancer Center, New York, NY, 3Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY
Purpose/Objective(s): Partial breast irradiation (PBI) is recommended as a preferred alternative over whole breast irradiation for patients with T1N0, low-grade, hormone-receptor positive invasive ductal breast cancers without LVI excised with negative margins, and for patients with “good risk” DCIS. We hypothesized that the presence of close margins would not influence local recurrence risks adversely in patients treated with PBI.
Materials/Methods: Patients treated from 2008 – 2022 with PBI following breast conserving surgery for IDS or DCIS were identified in a prospectively-maintained institutional database. Locoregional recurrence (LRR) was the primary endpoint, analyzed using the cumulative incidence function treating death as a competing risk. Gray’s test and univariable competing risks regression were used to evaluate the association between local/any recurrence and patient characteristics. Due to the low number of events, a multivariable analysis was not conducted. There were 9 patients with bilateral disease with each side treated with PBI – these records were treated as independent. Close margin categories included <1mm invasive, <1mm DCIS, =2mm invasive or DCIS. Positive margins were a rarity (n=3) and were confirmed after review of pathology reports and were included in the analysis.
Results: Of 1236 treatment courses in 1227 patients who underwent PBI at our center, 101 had close (n=98)/positive (n=3) surgical margins. Among this study cohort, median age was 65, the median tumor size was 1.0 cm (IQR: 0.7, 1.58), and 84% were invasive breast cancer; nearly all had estrogen-receptor positive disease (98%) and most received endocrine therapy (79%). A majority of the study cohort (79%) were low grade. With a median follow-up of 2.01 years (95% CI 1.88-2.24), there were 9 local recurrences, 1 regional recurrence (followed by distant recurrence), and 1 distant recurrence (total of 11 recurrences) across the entire cohort. Of the local recurrences, 1 occurred amongst patient with close margins and one occurred in a patient with a positive margin. The 5 and 10-year incidence of local recurrence in the entire cohort was 1.3% and 2.3%, respectively, and of any recurrence was 1.6% and 2.7%. In a univariable analysis, larger tumor size (p=0.036) and high-grade disease (p=0.014) were associated with increased risk of local recurrence, while close/positive margins was not associated (p=0.12). Close/positive margins (p=0.014), pathological size (p=0.049), and high-grade disease (p<0.001) were significantly associated with any recurrence.
Conclusion: Local recurrences were generally rare in our cohort of patients treated with PBI, suggesting that this treatment approach is reasonable within this common group of patients. However, patients with positive margins should not be offered PBI, consistent with current expert consensus. Furthermore, candidacy for PBI in patients with close margins in the presence of other adverse risk factors should be considered with caution.