Three interphase CDKs (CDK2, CDK4, and CDK6), mitotic CDK1, and 4 different classes of cyclins (Cyclin A, Cyclin B, Cyclin D, and Cyclin E) are directly involved in driving the cell cycle and the aberrant expression of the CDK-cyclin complexes resulting from cancer-associated mutations induces unscheduled re-entry into the cell cycle or proliferation34. Here, CDK4 is linked to cancer.