New therapeutic challenges in metastatic breast cancer: the association of CDK4 / 6 inhibitors with radiotherapy. A short review

FDA approval of CDK4 / 6 inhibitors (Palbociclib, Ribociclib and Abemaciclib) for metastatic and advanced breast cancer, in combination or not with Fulvestrant or Letrozole, has improved the prognosis of this type of patient population. Palliative radiotherapy with antalgic purpose in most of the cases is often part of the multidisciplinary treatment of bone involvement metastatic breast cancer. In the context of the approval of these innovative therapies and of the development of radiotherapy techniques, including stereotactic radiosurgery, it is necessary to identify the best therapeutic sequence and parameters (dose, volume, fraction size) to obtain a synergistic effect. Considering the toxicity profiles of new therapies (especially lymphopenia and neutropenia) and the different mechanisms of the induction of these toxicities towards radiotherapy and chemotherapy, it is also necessary to demonstrate the safety profile of concomitant or sequential irradiation with the administration of CDK4 / 6 inhibitors in combination with radiation therapy.