Study on the Safety and Tolerability of Postoperative Radiotherapy Concurrent With CDK4/6 Inhibitors in HR+/HER2- High-Risk Breast Cancer

1. The screening and evaluation of patients are conducted within 28 days prior to their enrollment, with the investigator screening subjects who meet the inclusion criteria. Prior to initiating any study-specific procedures or assessments, it is mandatory to obtain a signed informed consent form (ICF) from the subjects. Suitable candidates are selected through a series of consultations and examinations, which include inquiries about the patient's personal information, medical history, family history, marital and reproductive history, postoperative pathology, electrocardiogram (ECG), CT scans, complete blood count (CBC), blood biochemistry, and other relevant laboratory tests, to determine whether the subjects are eligible for enrollment in this study. 2. The patient is orally administered the CDK4/6 inhibitor determined by the dose escalation model one day before radiotherapy. During radiotherapy, patient visits are conducted weekly (±2 days) to record vital signs, adverse reactions, and related management measures, specifically at the following times: 7 days before the start of radiotherapy, the 10th day of radiotherapy, the 20th day of radiotherapy, and the 30th day of radiotherapy. If the patient's radiotherapy is delayed for any reason, the follow-up time should be postponed according to the actual situation. PRO scale questionnaires (FACT-B, FACT-ES, FACT-F) are assessed one day before radiotherapy, on the 14th day of radiotherapy, and on the 28th day of radiotherapy. Follow-up evaluations and PRO scale questionnaire assessments are conducted 2 weeks and 4 weeks after the completion of the combined treatment regimen. After completing the 4-week follow-up period of the combination therapy, the patient may resume the normal oral dosage of CDK4/6 inhibitor medication. 3. Evaluate efficacy and safety through statistical methods to form research conclusions. Conduct data cleaning and preprocessing, safety analysis (incidence and severity of AEs; analysis of the correlation between serious adverse events and treatment), and summarize and report the results.