These include cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i), which emerged onto the Canadian breast cancer treatment landscape in 2016 with the approval of palbociclib for the first-line treatment of HR+/HER2– metastatic breast cancer in postmenopausal women [6], followed by ribociclib in 2018 [7] and abemaciclib in 2019 [8]. The gene discussed is CDK4; the disease is breast cancer.