Metastatic breast cancer is generally regarded as incurable. A subset of these patients presents with oligometastasic. We wanted to describe patient, disease and treatment characteristics of this subgroup and identify their long-term outcome and prognostic factors.
We retrospectively selected patients diagnosed with synchronous metastatic breast cancer in our institution over the past 15 years who underwent resection of the primary tumour. Exclusion criteria were non-radical breast surgery, number of metastatic lesions >5 and number of organs involved >3. Kaplan-Meier method was used for progression-free survival (PFS) and overall survival (OS) analysis. Univariate and multivariate analysis were performed with Cox proportional hazards model. A p-value <0.05 was considered statistically significant.
Sixty-five patients were included in the study. After a median follow-up of 77 months, PFS-rate was 46% and OS-rate was 63%. In univariate analysis, PFSwas significantly longerfor patients who underwent additional local treatment for metastases (n = 40/65; treatment modalities including radiotherapy, surgery and/or radiofrequency ablation) (hazard ratio (HR) 0.32, p = 0.001), endocrine receptor positive breast cancer (HR 0.44, p = 0.047) and invasive ductal carcinoma compared to other histological subtypes (HR 0.32, p = 0.016). A trend towards better PFS was additionally seen in premenopausal patients, HER2-positive tumours and patients selected for local therapy for metastases after neoadjuvant chemotherapy or endocrine treatment. Only local treatment for metastases correlated significantly with better OS (HR 0.25, p = 0.002). After correction for endocrine receptor positivity in multivariate analysis, local treatment for metastases remained a significant predictor of PFS (HR 0.33, p = 0,002) and OS (HR 0.26, p = 0.002).
Our data suggest that a significant proportion of highly selected oligometastatic breast cancer patients experience long term remission. In the oligometastatic population who underwent surgery of the primary tumour with curative intent, local therapy for metastases is an independent predictor of better PFS and OS. Ongoing and future efforts will better delineate the optimal patient population where significant benefit of this approach can be achieved, while avoiding morbidity of multimodality treatment in patients who will not encounter long-term disease control.