PATINA (Randomized, Open-Label, Clinical Study of the Targeted Therapy, Palbociclib, to Treat Metastatic Breast Cancer) and MONARCHER (Study of Abemaciclib (LY2835219) in Women With HR+, HER2+ Locally Advanced or Metastatic Breast Cancer) are current studies in progress determining the response to management with trastuzumab and CDK4/6 inhibitors [23]. This evidence concerns the gene CDK4 and breast cancer.