Hormone Receptor–Positive HER2-Negative Oligometastatic Breast Cancer: prognostic stratification and pattern of progression

BACKGROUND: The management of oligometastatic breast cancer (OMBC) remains controversial, particularly regarding selection for local ablative treatment (LAT). In HR+/HER2- OMBC, where prolonged survival is often the case, improved stratification and characterization of progression may guide treatment. We aimed to define prognostic subsets, assess the contribution of Modern-Imaging-Methods (MIMs; 18F-FDG-PET/CT or WB-MRI) to LAT selection, and describe progression after first-line therapy in these subgroups of patients. MATERIALS AND METHODS: All consecutive patients with HR+/HER2- OMBC treated at our institution between 2012 and 2020 were included. OMBC was defined as ≤ 5 metastases. Prognostic factors including biological subtype, anatomical distribution, imaging modality, and LAT were evaluated for overall and progression-free survival (OS, PFS). RESULTS: Among 145 patients (median follow-up 82.8 months), median OS and PFS were, respectively, 81.1 and 26.5 months. Luminal-A-like subtypes, absence of liver metastases, and use of MIMs independently predicted better survival. LAT improved PFS (hazard ratio [HR]=0.52; 95%CI[0.29-0.91], p=0.0233) and showed a trend toward longer OS. In patients staged with MIMs, LAT significantly improved both OS (HR = 0.29; 95%CI[0.12-0.73], p=0.008) and PFS (HR = 0.40; 95%CI[0.21-0.77], p=0.0064). After first-line systemic therapy, only 18% developed polymetastatic progression. CONCLUSION: In HR+/HER2- OMBC, three actionable considerations emerge: staging must incorporate modern imaging to accurately define metastatic burden; LAT may be considered in selected patients with low-grade disease, absence of liver metastases, and long disease-free interval; in oligoprogression after first-line therapy, LAT should be re-evaluated within a multidisciplinary setting. These data offer pragmatic benchmarks to individualize treatment while awaiting definitive randomized evidence.