Review this case study to help familiarize yourself on how to monitor and manage your patients taking CDK4/6 inhibitor therapy. Mrs. Jones is a 66-year-old postmenopausal woman who developed left breast pain and a palpable mass. A mammogram and ultrasound showed a 4.6 cm mass with an enlarged axillary node. A core biopsy revealed invasive ductal carcinoma that is estrogen receptor positive, progesterone receptor positive, and HER2 negative. Positron-emission tomography and computed tomography scans revealed metastatic disease.