Bahrain Oncology Center Muharraq, Dahiyat Al-Rashe
M. S. Qamber1, L. Wahbeh1, S. abu Taha1, A. Alzibdeh2, M. Mukahal1, F. J. Abuhijla1, H. Al Masri1, B. Sharaf3, S. Abdel Al4, C. S. Shah5, and W. A. Asha1; 1Department of Radiation Oncology, King Hussein Cancer Center, Amman, Jordan, 2King Hussein Cancer Center, Amman, Jordan, 3Department of Medical Oncology, King Hussein Cancer Center, Amman, Jordan, 4Department of Orthopedics Surgery, King Hussein Cancer Center, Amman, Jordan, 5Department of Radiation Oncology, Cleveland Clinic Foundation, Cleveland, OH
Purpose/Objective(s): Despite the growing use of SBRT for various cancer types, its role in the management of metastatic breast cancer remains unclear, with mixed results including recent negative prospective trials. One challenge has been identifying a subgroup of metastatic breast patients that benefit from SBRT. We sought to evaluate outcomes with SBRT in metastatic breast cancer and to identify patient subgroups most likely to benefit from SBRT. Materials/
Methods: We conducted a retrospective analysis of metastatic breast cancer patients who received extracranial SBRT at a single institution. SBRT doses varied between 24Gy and 60Gy, administered in 2-5 fractions. Kaplan-Meier was used to calculate Overall Survival (OS), Local Control (LC), Distant Metastasis-Free Survival (DFS), and the likelihood of initiating or modifying systemic therapy over time. Univariate and multivariable analyses were also performed to explore associations between variables. Results: Between 2020 and 2023, 30 patients were treated with 25 being oligometastatic and 5 having oligoprogressive disease. A total of 45 lesions were treated, with bone lesions predominant (42/45 lesions, 93.3%). Luminal A subtype was the most common (n=21, 70%). After a median follow up of 13.8 months, one and two-year OS and LC rates were 84.2% and 93.2%, respectively while DFS was 68.5%/46.7%. Overall, 20 patients either stayed on their initial systemic therapy (n=17) or did not start systemic therapy following SBRT (n=3). For these patients, the OS rate was 89.1% at 1 and 2 years. However, for the seven patients requiring a change. in systemic treatment the OS was 64.3% at 1 and 2 years (p =0.35). One-year DFS/OS rates according to molecular subtype were 70%/82% Luminal A, 100%/100% for Luminal B, 66.7%/100% Basal, and 50%/50% HER2-neu enriched (p=0.2 for DFS and 0.5 for OS). On multivariable analysis, bone SBRT, was the only significant predictor of improved OS (p=0.01). Conclusion: SBRT in oligometastatic and oligoprogressive breast cancer offers promising LC rates and lessens the need for initiating or changing systemic treatments. Developing a nomogram for personalized DFS and OS predictions post-SBRT in metastatic breast cancer is essential for future advancements and patient selection.