周期蛋白依赖性激酶（CDK）4/6是细胞周期的关键调节因子，能够触发细胞周期从生长期（G₁期）向DNA复制期（S₁期）转变。在雌激素受体阳性（ER⁺）乳腺癌中，CDK4/6的过度活跃非常频繁。palbocicib是一种口服的CDK4/6抑制剂，能够选择性抑制CDK4/6，恢复细胞周期控制，阻断肿瘤细胞增殖。从Ⅱ期临床实验结果来看，palbociclib的临床疗效具有非常明显的优势。

Cycle dependent protein kinase (CDK) 4/6 is the key regulatory factor to cell cycle, and can trigger cell cycle phase to change from growth period (G₁ phase) to the DNA replication period (S₁ phase). In the estrogen receptor (ER⁺) breast cancer, the hyperactivity of CDK4/6 is very frequent. Palbocicib is an oral CDK4/6 inhibitor, which can selectively inhibit CDK4/6, and restore the control of cell cycle, therefore to block the proliferation of tumor cells. From the results of Ⅱ period clinical trials, the clinical efficacy of palbociclib has obvious advantages.