Aggressive local therapy for metastatic breast cancer: Challenges and updates (Review).

Systemic therapy has been viewed as the mainstay for metastatic breast cancer (dnMBC). However, as dnMBC is highly heterogeneous both biologically and clinically, and with ever-improving systemic strategies, it has been implied that the local therapy of the primary tumor (PT) may be beneficial for certain patients with dnMBC. However, the results from retrospective studies have been questioned due to their selection bias and retrospective nature. To the best of our knowledge, there are two published randomized clinical trials addressing this issue with conflicting conclusions: i) TATA study from India indicated no overall survival (OS) superiority with early local radiotherapy (LRT); and ii) MF07-01 indicated a 5-year OS rate improvement of 17% with upfront LRT. The updated results of a randomized phase III ECOG-ACRIN E2108 trial released in the 2020 American Society of Clinical Oncology (ASCO) meeting reported a negative survival effect of early LRT treatment in patients with dnMBC responding to initial systemic treatment, despite LRT significantly reducing the locoregional failure. Thus, a number of issues, such as the exact value of LRT, the optimal means of LRT (surgery and/or RT to the PT), the ideal timing of LRT and the population most likely to benefit from LRT, warrant further investigation. Herein, the related studies focusing on these aspects were comprehensively reviewed and a decision algorithm was proposed to select suitable patients with dnMBC for reasonable LRT. Generally, upfront systemic therapy is recommended. For good respondents and a subgroup of favorable profiles (young age, good general condition, low tumor burden, hormone receptor-positive and so on), radical LRT including PT surgery followed by RT and the resection of distant metastases is recommended. LRT should also be administered if the PT is still symptomatic. LRT may benefit patients with dnMBC due to the following reasons: Control of the PT decreases tumor burden, eliminates the source of dissemination, enhances the sensitivity to therapy and exerts positive immunomodulation. Therefore, the treatment paradigm for dnMBC may change from 'palliative LRT' into 'curative LRT' in a highly selected entity with careful evaluation.