Abstract P5-12-29: Treatment outcomes of patients with de novo oligometastatic breast cancer treated with “curative intent” at a single institution

Abstract Background: De novo oligometastatic breast cancer (OMBC) is often defined as limited disease with up to five distant lesions in two or fewer organs at initial presentation. Studies have suggested overall favorable outcomes for OMBC patients, making curative intent treatment appealing. Trials have attempted to address primary surgery in all de novo MBC (not OMBC) and, separately, ablative metastasis-directed therapy in OMBC (not all de novo) without survival benefits. However, no trial has addressed the cumulative benefits of removing the primary tumor, ablating all detectable distant metastatic lesions, and optimal systemic therapy with molecular subtype-specific multidrug systemic therapy in de novo OMBC. Management of de novo OMBC remains controversial. We analyzed outcomes of patients with de novo OMBC treated with curative intent. Methods: We analyzed data for patients with de novo OMBC who were treated with physician-expressed curative intent at a single institution between 1/2000 – 12/2020. We identified patients by performing a simple keyword search within institutional electronic medical records that included physician-entered terms “oligometastases” AND “breast cancer” AND “curative intent” or “curative hope” and had at least one visit in clinic. Term variants such as “oligometastatic” for “oligometastases” were also included. All resulting charts were then manually reviewed for inclusion criteria. We more strictly defined OMBC as one organ (including bone) involved with metastatic lesions and 4 or fewer lesions per metastasized organ. All patients were required to have had definitive breast surgery for inclusion into the analytic cohort. Recurrence-free survival (RFS) and overall survival (OS), beginning at time of surgery, were evaluated using Kaplan-Meier methods. Results: A total of 39 patients were identified: 12 hormone-receptor (HR) positive (+)/HER2+, 2 HR negative (-)/HER2-, 21 HR+/HER2-, 4 HR-/HER2+. Most patients (33, 84.6%) had 1 oligometastatic lesion at diagnosis, 3 (7.7%) had 2 lesions, 2 (5.1%) had 3 lesions, and 1 (2.6%) had 4 lesions. 100% of patients underwent breast surgery; 15 (38.5%) underwent lumpectomy and 24 (61.5%) underwent mastectomy. Median age at time of surgery was 47 (range 28-69). Most patients (29, 74.4%) also underwent radiation therapy (RT) to the breast. Two-thirds of patients (26, 66.7%) underwent metastasis-directed therapy (MDT). The most common MDT type was RT (22/29, 75.9%). With median follow-up of 5.8 years (y), 27/39 (69%) patients had not recurred. Of 12 recurrences, 100% were new distant metastases. Median RFS was 7.1y (95% CI 4.87-not reached). Five-year RFS was 62% (95% CI 46-84%). Median RFS was 7.1y (95% CI 2.01-not reached) among HER2+ patients and 6.98y (95% CI 4.62-not reached) among HR+/HER2- patients. Landmark RFS was not impacted by whether a patient received MDT. Median OS was not reached (95% CI 7.42-not reached) and five-year OS was 77% (95% CI 61-95%). Conclusions: The use of curative intent treatment in OMBC at a single institution was most common in patients with a single metastasis in one organ. Survival outcomes were favorable among this highly select cohort of patients, with nearly two-thirds of patients free of relapse at 5y and similar RFS among the HER2+ and HR+/HER2- cohorts. Validation of these findings in prospective series and further studies evaluating optimal treatment strategies in this setting are needed. The benefits of primary surgery and MDT in this population remain unknown. Citation Format: Emily L. Chen, Hillary Heiling, Tianyu Li, Jennifer Bellon, Faina Nakhlis, Heather Parsons, Alyssa R. Martin, Harold Burstein, Sara M. Tolaney, Melissa Hughes, Nabihah Tayob, Nancy U. Lin, Sarah Sammons. Treatment outcomes of patients with de novo oligometastatic breast cancer treated with “curative intent” at a single institution [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P5-12-29.