Observational Clinical Study on Role of MRD in Predicting Local Therapy in Oligometastatic Breast Cancer

This is an observational study to investigate the correlation between MRD levels and prognosis in patients with locally treated oligometastases of breast cancer, who have no more than 5 systemic metastases of breast cancer, which may not be confined to the same organ (with the exception of brain metastases), and who have stable systemic control of the disease, and who are to undergo localised treatment. Subjects will read and fully consider the \"Informed Consent Form\" for this study, sign it in writing if they decide to participate in the study, and complete the Screening Visit no later than 28 days prior to the start of study treatment. For ethical reasons, the screening visit may not be repeated if it was performed prior to the signing of the Informed Consent Form. Subjects were asked to complete imaging and MRD testing prior to their first study treatment, and to undergo on-tumour imaging and MRD testing every 3 months (±7 days) for the duration of the study, and additional investigations or more frequent on-tumour imaging evaluations could be performed during the study based on clinical indications. During this period, subjects continued study treatment until disease progression occurred, toxicity was intolerable, the subject voluntarily withdrew informed consent, or the investigator determined that the subject needed to withdraw from the study. Subjects with disease progression or early withdrawal were also required to complete an exit visit and then enter safety follow-up.