2824 - Impact of Endocrine Therapy Adherence on Locoregional Recurrence following Accelerated Partial Breast Irradiation for Early-Stage Breast Cancer
Presenter(s)
E. E. Obi1, A. Bommireddy1, R. Matar-Ujvary2, Z. Al-Hilli2, J. Kocsis1, C. S. Shah3, and R. D. Tendulkar1; 1Department of Radiation Oncology, Cleveland Clinic Foundation, Cleveland, OH, 2Breast Center, Integrated Surgical Institute, Cleveland Clinic Foundation, Cleveland, OH, 3Allegheny Health Network Cancer Institute, Department of Radiation Oncology, Pittsburgh, PA
Purpose/Objective(s): Breast conservation surgery (BCS) followed by radiation therapy (RT) and endocrine therapy (ET) is standard of care for many patients with early stage hormone positive breast cancer (BC). Partial breast irradiation (PBI) has demonstrated similar oncologic outcomes to standard and hypofractionated whole breast RT regimens for patients with early-stage invasive breast cancer or ductal carcinoma in situ. The PRIME II trial demonstrated that elderly patients (pts) with favorable disease characteristics are eligible for omission of RT while accepting a small increased risk (up to 10% at 10 years) of local recurrence if adherent to ET. However, ET may cause significant side effects that can result in cessation of therapy, and further increasing local recurrence risk. This study investigates the risk of recurrence following BCS and PBI comparing high vs. low ET adherence.
Materials/Methods: All pts with invasive BC treated with BCS followed by PBI at a single tertiary care institution from 2018-2022 were identified. Inclusion criteria consisted of pts 65+ years with early stage (T1/T2N0), invasive, hormone-positive BC. PBI consisted of 30 Gy/5 fractions with IMRT or VMAT technique. Patients were stratified by ET use, defined by treatment duration over follow up time (up to five years): High ET adherence (>80% adherence) and Low ET adherence (<80% adherence). Locoregional failure free survival (LRFFS) was estimated using Kaplan–Meier analysis.
Results: A total of 198 pts were included in this study. Median age was 71 years old (range 65-88 years). Most patients had invasive ductal carcinoma (n=164, 83%) while a few patients had ILC (n=18, 9%) or mixed histology (n=16, 8%). Ninety-five percent (n=188) of patients were stage I and 5% (n=10) had stage II disease. Overall, 2.5% (n=5) were HER2+ with one receiving chemotherapy. Median follow up was 51 months. There were 138 pts in the high ET adherence cohort and 60 pts in the low ET adherence cohort. There was a significant difference in the LRFFS at 4 years between these two cohorts, with no recurrences observed in the high ET adherence cohort compared to two recurrences in the low ET adherence cohort respectively (LRFFS 100% v. 96% p= 0.03). Median time to recurrence was 36 months.
Conclusion: Our study shows that combining PBI and ET is associated with improved locoregional recurrence-free survival compared to PBI with low ET adherence. However, PBI with low ET adherence still had high rates of LRFFS of 96%, suggesting PBI alone may be a viable option for select patients who are unable to tolerate ET.