18F-FDG PET/CT Metabolic Response With Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative Breast Cancer Treated With Cyclin-Dependent 4/6 Kinase Inhibitors.

Dysregulation of the cyclin D-CDK4/6-INK4-RB pathway, which leads to uncontrolled cell proliferation, is frequently observed in breast cancer. Recently, 3 CDK4/6 inhibitors have been FDA approved as first-line treatment for patients with hormone receptor-positive, human epidermal growth factor receptor 2-negative advanced breast cancer. Despite promising clinical results, the metabolic response to treatment with these new drugs has not been elaborately demonstrated yet. Herein, we presented a patient with hormone receptor-positive, human epidermal growth factor receptor 2-negative breast cancer who demonstrated a complete metabolic response on 18F-FDG PET/CT to treatment with a CDK4/6 inhibitor (ribociclib).