2737 - Repeat Irradiation for In-Breast Tumor Recurrence Following Breast Conservation for Early Stage Breast Cancer
Presenter(s)
A. L. Frias1, S. Yee2, C. N. Day3, K. S. Corbin1, M. Mrdutt4, and M. Elbanna1; 1Department of Radiation Oncology, Mayo Clinic, Rochester, MN, 2Department of Surgery, Mayo Clinic, Rochester, MN, 3Department of Biomedical Statistics and Informatics, Mayo Clinic, Rochester, MN, 4Breast & Melanoma Surgical Oncology, Mayo Clinic, Rochester, MN
Purpose/Objective(s): For ipsilateral breast tumor recurrence (IBTR), second breast-conserving surgery (BCS) with re-irradiation (re-RT) is increasingly used. Hypofractionated once-daily RT is appealing but understudied in this setting as studies evaluating optimal dose schedule are ongoing. We report our institutional experience with repeat breast conservation and re-RT.
Materials/Methods: With IRB approval, patients treated with BCS for IBTR were identified. Prior recurrence or metastatic disease was excluded. Descriptive statistics summarized characteristics, and survival outcomes were estimated using Kaplan–Meier methods.
Results: 154 patients with 155 IBTR events after BCS were identified. 76 patients had prior RT. Among the 76 patients, IBTR events were invasive (62/76, 81.6%) and biologic subtype was 89% HR+/HER2-, 5% HER2+, and 7% TNBC. 1 patient (1.6%) was node positive. Re-RT was used in 39/76 (51%). Of 39 undergoing re-RT, median age at IBTR was 70.4 (IQR: 65.7, 76.7), median disease-free interval (DFI) 5.5 yrs (IQR: 2.9, 13.4) and median interval between RT 5.9 years (IQR: 3.6, 13.6).
In the 37 patients (49%) with re-RT omitted, treatment was not advised in 21 patients (57%), declined in 13 (35%), and rationale unclear in 3 (8%). Most frequently, RT was not advised because of prior history of RT in 9/21 (43%) and favorable biology in 7/21 (33%). These patients had a longer median DFI compared to the re-RT cohort-- 14.4 yrs (IQR: 4.7, 20.5) vs 5.5 yrs (IQR: 2.9, 13.4); p = 0.02. Among these 37 patients, 86.5% of IBTRs were invasive of which 97% were HR+/HER2-. Re-RT volumes were PBI in 22, WBI in 14, WBI+RN1 in 2, and axillary RT in 1. Among those receiving re-RT with WBI, 13/14 (93%) had PBI in the first course. Among 12 with modality data, photon re-RT was used in 10 (83%). Mean heart dose (MHD) was 0.5 Gy. Mean ipsilateral lung V40% and V20% were 6% and 12%. Among those receiving re-RT with PBI, 14 of 22 (70%) had prior WBI. Proton re-RT was used in 73%. MHD was 0.04 Gy. Mean ipsilateral lung V40% and V20% were 0.8% and 3%. Re-RT doses are shown in Table 1. In the re-RT patients, median follow-up was 2.6 years (IQR: 1.3, 3.6). Adjuvant ET was used in 21 of 37 patients with available data (56.8%). 5-year local recurrence free survival was 81% (95% CI: 50.6, 100.0). No patients progressed to distant disease.Conclusion: Among patients undergoing repeat BCS for IBTR, re-irradiation was offered to two-thirds with 39 treated, most commonly using PBI and ultrahypofractionated regimens. Toxicity outcomes are being analyzed to inform the feasibility and safety of short course re-RT in a prospective study.
Table 1 – Re-RT dose and fractionation *These patients received 26 Gy in 5 fx. 2 patients received a simultaneous integrated boost (SIB) to 30 Gy and 1 patient received a sequential boost to 36 Gy.| Modality | Dose (Gy) | Fx | N |
| WBI (N = 14) | 26 | 5 | 5 |
| 40.05 | 15 | 4 | |
| 30* | 5* | 2* | |
| 36* | 9* | 1* | |
| 42.56 | 16 | 1 | |
| 61 | NR | 1 | |
| PBI (N = 22) | 21.9 | 3 | 7 |
| 26 | 5 | 6 | |
| 40.05 | 15 | 4 | |
| 30 | 5 | 3 | |
| 42.56 | 16 | 1 | |
| 45 | 30 | 1 |