In this study, we demonstrated that the frequency of grade ≥ 3 hematologic toxicities, including anemia, neutropenia, and thrombocytopenia, did not increase in HR+ HER2-negative metastatic breast cancer patients receiving CDK4/6 inhibitors in combination with palliative radiotherapy compared to those not receiving radiotherapy. Here, ERBB2 is linked to Thrombocytopenia.