Abstract PO5-05-12: Loco-regional Treatment in De Novo Bone Only Metastatic Breast Cancer; Prospective, Multi-Institutional Real-World Data, BOMETIN, Protocol MF14-1a

Abstract

Abstract Introduction: The impact of loco-regional treatment (LRT) on survival in de novo bone-only metastatic breast cancer (BC) is controversial. The aim of this study is to assess the effect of LRT on survival utilizing international, prospectively acquired data in this cohort of patients. Materials and Methods: Patients with de novo metastatic BC with bone-only metastases were divided into two groups: those receiving systemic therapy only (ST) and those undergoing LRT. Patients who received LRT were divided into two groups: those who received ST after LRT (LRT+ST arm) and those who received ST prior to LRT (ST+LRT arm). Solitary or multiple bone metastases were classified, and factors associated with disease progression were analyzed. Results: There were a total of 744 patients with de novo bone-only metastatic BC treated at each of the participating institutions between 2014 and 2022, with 372 (50%) participants in each arm. Median follow-up was 48 months (32-66, 25-75%). Patients in the LRT group were significantly younger than the ST group [50 (42, 60) vs 55 (44, 66), p=0.0001]. There were no significant differences in grade, Her2 neu and triple negative status, receipt of hormonal therapy and intervention to metastatic sites. During follow-up, 58% (n=217) of patients in ST arm and 32% (n=120) of patients in LRT arm died (p< 0.001). Local progression was observed in 20% of the patients in the ST arm whereas it was 9% in the LRT arm (p=0.0001). Systemic progression occurred more in ST arm; 66% (n=244) compared to 41% (n=152) of patients in LRT group (p< 0.001). The Hazard of death was 64% lower in LRT group than in ST group (HR: 0.36, 95% CI: 0.29-0.45), p<0.0001). The burden of metastatic disease was significantly different between groups with the solitary bone metastasis rate higher in LRT group than the ST only group (50% vs 24%, p< 0.001). However, the LRT group had better overall survival for both solitary (HR: 0.38, 95% Cl: 0.26-0.55) and multiple (HR: 0.38, 95% Cl: 0.29-0.51) bone metastases patients. Within the LRT group, survival rates were similar whether the breast surgery was performed before or after ST.Multivariate Cox analysis showed that LRT and ER/PR positivity significantly decrease the hazard of death (p< 0.05). Conclusion: Analysis of this large multi-institutional patient cohort provides further evidence that LRT improves overall survival and lowers loco-regional recurrence in patients with de novo bone-only metastatic BC. In breast cancer patients with bone-only metastases at presentation, the decision for LRT should be made through a multidisciplinary approach with consideration of surgical therapy at the primary tumor. Citation Format: Atilla Soran, Serdar Ozbas, Lutfi Dogan, Didem Can Trabulus, Jamila El-Azrhi, Kazim Senol, Berk Goktepe, Shruti Zaveri, Salyna Meas, Umut Demirci, Hasan Karanlik, Aykut Soyder, Ahmet Dağ, Ahmet Bilici, Mutlu Dogan, Mehmet Ali Nahit Sendur, Hande Koksal, Mehmet Ali Gulcelik, Neslihan Cabıoğlu, Levent Yeniay, N. Zafer Utkan, Nuri Karadurmus, Gul Daglar, Turgay Simsek, Birol Yildiz, Cihan Uras, Mustafa Tukenmez, Cihangir Ozaslan, Niyazi Karaman, Arda Isik, Berkay Demirors, Efe Sezgin, Vahit Ozmen, Anthony Lucci. Loco-regional Treatment in De Novo Bone Only Metastatic Breast Cancer; Prospective, Multi-Institutional Real-World Data, BOMETIN, Protocol MF14-1a [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-05-12.