This is an observational clinical study of MRD as a predictor of local treatment in patients with oligometastatic breast cancer. The aim of the study is to assess the correlation between MRD levels and prognosis in patients with oligometastatic breast cancer who have undergone local treatment in order to identify the population that would benefit from local treatment and to develop an individualised treatment plan. Subjects will agree to participate in this study and will be asked to collect as much medical history and demographic information as possible prior to enrolment to confirm that they meet the inclusion/exclusion criteria, and that they will undergo imaging and MRD testing prior to their first study treatment. Furthermore, subjects will undergo tumour imaging and MRD testing every 3 months (±7 days) after MRD treatment for the duration of the study, with additional investigations or more frequent tumour imaging evaluations as clinically indicated during the study.