First clinical experience with CDK4/6 inhibitors in breast cancer therapy.

For hormone receptor-positive, HER2-negative breast cancer patients with metastatic or advanced disease, therapy with CDK4/6 inhibitors in addition to aromatase inhibitors (AIs) or to the estrogen receptor (ER) downregulator fulvestrant has resulted in an additional therapy option and a longer progression-free survival. In the Gynecologic-Oncology Clinic, Diakonie-Klinikum Schwabisch Hall, we followed and registered our initial clinical experience with CDK4/6 inhibitors, following the side effects and tumor response over two years since they were officially approved for general use in Germany. Differences were observed when palbociclib or ribociclib was used in combination with letrozole or anastrozole or fulvestrant. The dynamic side effects and tumor response under therapy with palbociclib or ribociclib were found to be comparable with the main reported data in the official drug information. The CDK4/6 inhibitors have an important and promising role in the therapy of breast cancer patients. Patient age and therapy duration do not influence the use of palbociclib or ribociclib, although it may be important which AI is used in combination with palbociclib.