2952 - Evaluating Patterns of Breast Cancer Recurrence following Neoadjuvant Systemic Therapy and Lumpectomy
Presenter(s)
A. Kassardjian1, S. Yoon1, P. Wu1, S. M. Glaser1, W. T. Watkins1, S. Bhardwaj2, J. Rand3, I. Washington4, and J. G. Bazan Jr1; 1Department of Radiation Oncology, City of Hope National Medical Center, Duarte, CA, 2Department of Medical Oncology, City of Hope National Medical Center, Duarte, CA, 3Department of Surgery, City of Hope National Medical Center, Duarte, CA, 4H. Lee Moffitt Cancer Center and Research Institute, Department of Radiation Oncology, Tampa, FL
Purpose/Objective(s): Breast cancer patients with stage I, node-negative, hormone-receptor positive (HR+)/HER2- treated with upfront breast conserving surgery (BCS) often receive accelerated partial breast irradiation (APBI) as an alternative to whole breast irradiation (WBI). Patients who respond to neoadjuvant systemic therapy (NST) and have a pathologic complete response (pCR) or minimal residual disease in the breast may also benefit from APBI. However, patients receiving NST were excluded from the APBI trials, and there are minimal data regarding in-breast tumor recurrence (IBTR) and local-regional recurrence (LRR) in the era of modern NST. Here, we characterize patterns of failure in patients receiving NST, BCS, and adjuvant radiation therapy (RT) with a goal of identifying a subgroup of patients in which prospective evaluation of APBI may be suitable to study.
Materials/Methods: We examined breast cancer patients at a single comprehensive cancer center treated with NST, BCS, and RT from 2017-2021. We captured demographics, basic clinical and pathological variables, NST regimens, RT details, and outcomes, including IBTR, LRR, distant metastases (DM) and overall survival (OS). We defined a low-risk (LR) group as: pCR with =ypT1c disease confirmed to be both cN0 and ypN0. All other patients were considered high-risk (HR). The primary outcome assessed was the cumulative incidence of IBTR. Secondary outcomes included LRR, DM, any breast cancer recurrence (BCR), and OS. The log-rank test was used to compare LR and HR groups.
Results: A total of 321 patients met the study criteria. Median age was 55 [IQR 48-64] years, 216 patients (67.3%) were post-menopausal, and the majority were either Hispanic (36%, N=116) or non-Hispanic White (33%, N=106). Breast cancer subtype was evenly distributed with 36% (N=115) triple-negative, 33% (N=106) HER2+, and 31% (N=100) HR+/HER2-. Median follow-up was 47 months [IQR 37-61 months]. There were 186 patients (57.9%) in the LR group (138 with pCR) with 44% (N=81) triple-negative, 41% (N=76) HER2+, and 16% (N=29) HR+/HER2-. All patients received WBI, 53.5% received regional nodal irradiation, and 88.2% received a cavity boost. The overall 4-year IBTR rate was 1.6% (95% CI 0.6% - 3.5%). While there was no significant difference between the LR and HR cohorts in 4-year cumulative incidence of IBTR (1.1% vs. 2.3%, p=0.29) or LRR (2.3% vs. 4.1%, p=0.44), all other outcomes significantly favored the LR cohort (4-year DM=1.6% vs. 14.9%, p<0.0001; 4-year BCR 3.9% vs. 15.7%, p=0.0003; 4-year OS 98.0% vs. 89.2%, p=0.014).
Conclusion: In the modern era, patients with pCR or node-negative disease with minimal residual disease in the breast have low rates of recurrence and excellent cancer control outcomes. Our findings suggest that it may be safe to de-escalate radiation therapy with APBI in these LR patients with predominantly triple-negative and HER2+ breast cancer. Based on our results, prospective evaluation of APBI after NST is ongoing.