Tumor tissues were fixed in 10% formalin and embedded in paraffin, sliced into 4 μm sections, deparaffinized, dehydrated, antigen retrieved, blocked with 5% goat serum, and incubated in the primary antibodies: anti-RB1 (1: 500; CST), anti-CDK2 (1:50; Abcam), anti-CDK4 (1: 500; CST), anti-CDK6 (1: 100 Abcam). Here, CDK4 is linked to neoplasm.