Differential efficacy of newly registered therapies in subgroups of metastatic breast cancer (mBC) is an important consideration for their subsequent use in clinical practice. In a systematic literature review, we evaluated differences in outcome regarding progression free survival (PFS), time to progression (TTP), overall survival (OS) and visceral versus non-visceral disease. The impact of HER2- and hormone receptor-status was also considered.
A systematic literature search (6362 hits) in the meta-Database PubMed was performed for the last 20 years. 257 studies (n = 126,291) were included for further analysis. 69 studies had published data for visceral vs non visceral disease including phase III trials. Out of these 69 studies we selected n = 16 studies (n = 13,083) which looked at the endpoints mentioned above. In order to achieve comparability, we extracted the information of hazard ratios (HR), confidence intervals (CI) and times in weeks (if available) for PFS, TTP, OS of the entire study population, which was divided into three groups: HER2-positive, HER2-negative, unknown HER2 status.
No statistically significant difference in treatment response was found in mBC patients looking at HRs and CIs. Relevant, yet not statistically significant differences were found in the specific response of visceral metastases to modern combination therapies, especially in HER2-positive breast cancer: There was a benefit regarding OS using lapatinib combined with trastuzumab or trastuzumab and docetaxel combined with pertuzumab. Additionally, in two chemotherapy trials, there was a numerical difference between therapy response in visceral vs. non-visceral metastases regarding PFS in the unknown HER2 group, and regarding OS in the HER2 negative group.
In the subgroup analyses, we did not find any significant differences in response rates for visceral vs. non-visceral metastasis. There seems to be a beneficial effect of combination therapies regarding OS in visceral disease. At the present time, metastasis localization should not be used as a predictive marker for choice of systemic therapy in mBC.
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All authors have declared no conflicts of interest.