2953 - Outcomes of Proton Therapy for Oligo-Adjacent Breast Cancer: A Multi-Institutional Evaluation
Presenter(s)
A. C. Kessel1, E. Braschi Jordan2, W. S. Harmsen3, R. O. Kowalchuk1, J. A. Bradley2, A. W. LaVigne4, K. S. Corbin1, J. L. Wright4, and R. B. Jimenez5; 1Department of Radiation Oncology, Mayo Clinic, Rochester, MN, 2Department of Radiation Oncology, University of Florida College of Medicine, Gainesville, FL, 3Mayo Clinic Rochester, Rochester, MN, 4Department of Radiation Oncology, Johns Hopkins University School of Medicine, Baltimore, MD, 5Department of Radiation Oncology, Massachusetts General Hospital, Boston, MA
Purpose/Objective(s): Studies have demonstrated improved overall survival (OS) in patients with oligometastatic cancer treated with metastasis directed therapy (MDT) with radiation (SABR-COMET). However, the NRG-BR002/CURB trials did not demonstrate a progression free or OS survival benefit in patients with oligometastatic breast cancer (OMBC). Although few studies have evaluated patients with OMBC with a more favorable metastatic profile (those with metastases adjacent to traditional radiation fields), these patients are often treated with definitive intent. Proton radiation therapy (PRT) can facilitate coverage of “oligo-adjacent” breast cancer and may reduce toxicity by sparing normal tissue. We evaluated the outcomes of patients with OMBC treated with definitive proton therapy to the primary disease and adjacent metastatic lesion(s) at 4 academic centers between 2014-2023.
Materials/Methods:
Patients with OMBC treated with definitive intent to the primary disease and synchronous adjacent metastatic lesion(s) with a single proton therapy plan, without distant metastatic disease, were eligible. Clinicopathologic and outcome data were evaluated. The primary outcome of interest was progression free survival (PFS). Additional outcomes were OS and toxicity.Results: Forty-five patients (median age 48, range 29-74) were included. 40/45 (89%) had de novo OMBC at the time of proton therapy; the remaining 5 patients had oligorecurrent cancer. Most (40) received chemotherapy prior to radiation and all had surgery. Sixteen patients received treatment inclusive of the ribs and/or sternum and 29 to adjacent lymph nodes regions. Median prescription dose was 60GyE (range 48-70). Most patients received conventionally fractionated proton therapy; hypofractionation was used in 13% of patients.
At a median follow-up of 3.8 years (IQR 2.4-5.3), 37/45 (82%) were alive, and 31/45 (69%) were without evidence of progression. Median PFS was not reached. At 1 and 3 years, PFS was 77.0% and 66.1% and OS was 88.1% and 82.3%, respectively. Patients with estrogen receptor (ER) negative disease had a greater risk of progression (HR 5.24, 95% CI 1.68-18.36, p = 0.03). At one year, there was a trend towards greater risk of progression for patients with non-regional nodal disease (68.9%) vs bone disease (93.3%) and oligorecurrent disease (50%) vs de novo (79.7%), but not statistically significant. All grade toxicity was overall low, with notable toxicities of any chest wall fibrosis (42%), implant loss (4%), rib fracture (2%), and radiation pneumonitis (2%).Conclusion: In this select group of patients with oligo-adjacent OMBC treated with definitive PRT, PFS rates were improved compared to historical PFS <24 months with MDT in breast cancer (SABR, CURB, BR002). Carefully selected patients with OMBC may benefit from definitive therapy, with PRT techniques facilitating comprehensive target coverage and toxicity minimization.