Prognostic factors in hormone receptor positive oligometastatic breast cancer.

1058 Background: Some recommend curative treatment for oligometastatic breast cancer (OMBC). To date, no randomized clinical trial has demonstrated the benefits of such a strategy. We present the largest retrospective series of patients treated consecutively for ER and/or PR positive (HR+) OMBC in a single institution. The objective was to describe the clinical and biological characteristics and prognostic factors of HR+ OMBC. Methods: We retrospectively reviewed all patients treated consecutively from 2014 to 2018 at our institution for synchronous or metachronous metastatic breast cancer (MBC). HR+ OMBC was defined as MBC with up to five metastases at diagnosis, positive hormone receptor status, and no other inclusion criteria. Clinical and biological characteristics, treatment modalities - intent-to-cure vs palliative - and outcomes were recorded. Progression-free survival (PFS) and overall survival (OS) were calculated. Log rank test and Cox regression models were used for survival analyses including time-dependent variable. Results: Of 998 patients treated for MBC within our institution between 2014 and 2018, 11.3% (N=113/998) met inclusion criteria. 62.5% of them had SBR grade I/II HR+ OMBC and 80.5% had HR+/HER2- OMBC. 89.3% patients had only one organ involved. None had more than two; 89.3% patients had 1-3 metastases at diagnosis. Among these 113 patients, 63.7% had bone metastases, 54.9% had bone only metastases, 19.5% had visceral metastases, 17.7% had lymph node metastases, 7.1% had brain metastases, and 3.5% had other metastases. Forty-one patients (36.3%) were treated in a curative intent with systemic treatment plus ablative focal treatment of primary tumor – or local relapse – and all distant metastases. Median follow up was 67.2 months (95%CI= [63.1-75.4]). For the entire series, five-year PFS and OS were respectively 35.2% (95%CI= [25.6-44.6]) and 67.0% (95%CI= [56.7-75.3]) respectively. In univariable analysis, liver metastases was associated with worse OS (HR=3.13, 95%CI=[1.43-6.87], p=0.003). In multivariable analysis, HER2 positive status (HR=0.43, 95%CI= [0.21-0.90], p=0.024), bone only metastases (HR=0.46, 95%CI= [0.27-0.78], p=0.004), and intent-to-cure treatment (HR=0.53, 95%CI= [0.30-0.93], p=0.027) were significantly associated with longer PFS. In multivariate analysis, only intent-to-cure strategy was associated with better OS (HR=0.24, 95%CI= [0.09-0.60], p=0.002). Conclusions: This is the largest retrospective series of patients treated consecutively for HR+ OMBC to date. 71.5 % of OMBC and 11.3 % of all MBC are HR+ OMBC. Most had only one invaded organ and 1-3 metastases. Among our cohort, intent-to-cure treatment improve drastically HR+ OMBC PFS and OS. A multimodal intent-to-cure strategy should be routinely discussed for patients with HR+ metastatic breast cancer with one to five metastases at diagnosis.