Metastasis-directed therapy for oligometastases in breast cancer

The concept of oligometastases was first proposed to describe a disease state between localized cancer and extensive metastasis. After the emergence of variations in the definition of oligometastasis, in April 2020 the European Society for Radiotherapy and Oncology and the European Organization for Research and Treatment of Cancer defined oligometastases as the presence of one to five metastatic lesions that can be safely treated. However, the pathogenesis of oligometastases remains unknown, and it is uncertain which patients will benefit from metastasis-directed therapy. Breast cancer with oligometastases is generally managed with systemic therapy. Retrospective studies have suggested that the addition of metastasis-directed therapy, such as surgery, radiofrequency ablation and stereotactic body radiation therapy, may increase overall survival in breast cancer patients with oligometastases, but as yet there have been no prospective studies. Phase II trials of stereotactic body radiation therapy or fractionated irradiation for oligometastases of breast cancer have demonstrated impressive rates of local control and overall survival. Although the efficacy of stereotactic body radiation therapy in the SABR-COMET was largely anticipated, it is noteworthy that only 18% of the patient population had breast cancer. For this reason, various trials were planned or are being conducted globally to investigate the efficacy of metastasis-directed therapy for oligometastases of breast cancer. Metastasis-directed therapy for oligometastases has been shown to be effective, and stereotactic body radiation therapy and other therapies are commonly used internationally and are considered to be safe. However, the efficacy of metastasis-directed therapy for oligometastases has not yet been proven. The results of future clinical trials are thus eagerly awaited.