CDK5R1 and breast cancer: Hyperactivation and overexpression of CDK5, as well as its activators p35 and p39, are frequently observed in colon cancer [23], breast cancer [24], lung cancer [25], thyroid cancer [26], pituitary adenoma [27] and prostate cancer [28], which regulate series events of cancer progression including proliferation, DNA damage response (DDR), apoptosis, migration, angiogenesis and immune evasion.