Impact of oligometastatic disease on survival in ER positive breast cancer: A population-based analysis.

Abstract

e19109 Background: Estrogen positive (ER) advanced breast cancers (ABC) are associated with a longer survival compared to other subtypes. However, clinical equipoise remains for the management of oligometastatic disease. While recent phase I and II data support the use of metastasis-directed therapy, breast cancer patients remain underrepresented and real-world outcomes for breast cancer patients with directed treatment for oligometastases is lacking. Methods: The BC Cancer Breast Cancer Outcomes Unit (BCOU) database was utilized to identify patients with ER positive breast cancer referred to BC Cancer from 2005-2014 with documented metastases. Baseline clinical, pathological and treatment data were compiled. Overall survival (OS) was compared between the group with oligometastatic disease(OM) (defined as < = 5 foci of metastases) and the group with non-oligometastatic disease (defined as > = 6 foci of metastases) using Kaplan-Meier survival curves. Key secondary endpoints included metastasis-directed treatment impact, based on the site of metastasis, local control (LC) and distant failure (DF) rate. Results: A total of 938 patients met the inclusion criteria. Of these, 191 (20.4%) had OM and 747 (79.6%) had widespread disease at 1st diagnosis of ABC. The groups were well balanced for clinical characteristics (all p > 0.05), with a median age of 59yrs (23-99). 84% were ductal carcinomas, 14% were also HER2 positive. Sites of oligometastases were bone (66.5%), liver (12.0%), brain (8.4%) and lung (5.8%). Median follow-up was 7.4 yrs. Median OS was 24 mo (95% CI 20.2, 27.8) for patients with OM and 11 mo (9.5, 12.5) for those with widespread disease (p < 0.0001). In the OM group, 114 (59.7%) of patients received metastasis-directed treatment, whereas 77 (40.3%) did not. Treatment modalities included radiation in 53.4% of patients, surgery in 8.9% of patients and stereotactic body radiotherapy (SBRT) in 3.7%. Median OS was 24 mo (18.3, 29.7) for patients who received metastasis-directed treatment and 23 mo (17.5, 28.5) for those who did not (p = 0.954). Patients with bone-only metastases had a median OS of 27mo with directed treatment and 25mo without directed-treatment (p = 0.334). Conclusions: Oligometastatic state was associated with a significantly better OS. Metastasis-directed treatment was associated with a non-significant OS difference in patients with bone-only metastases in a real world cohort. However, the impact of modern systemic treatment and SBRT methods are evolving. Large prospective randomized studies of this approach merit further study.