Preoperative Radiotherapy and Systemic Therapy Following Surgery in 'de Novo' Metastatic Breast Cancer

"Oligometastatic disease (defined here as 5 or fewer sites of metastatic disease involving 3 or fewer organ systems)~* Primary tumor biopsy, Metastatic site biopsy (Bone, liver, etc) (if there is, based on institutional practice)~ o ER / PR /Her2 /Ki67 study)~* Collection of CTC.~* Radiotherapy (RT) to the primary breast tumor (Hypo fractionated)~* All patients will receive the standard of care treatment with CDK4/6 inhibitor + AI for 6 months (at least 26 weeks).~ o Denosumab, Biphosphonate for bone metastasis~* RT to metastatic side (if visible). Continue Systemic therapy~* 12 months, patients will have LRT surgery (BCS/mastectomy + LN evaluation; SLNB+ALND) + RT (based on the institutional practice). Collect CTC and ER/PR/Her 2 in the final specimen~* ST will be continued until progression and/or unmanageable toxicity.~* Radiologic evaluation every 3-6-month based on institutional practice."