CDK4 and breast cancer: This impact of GIV on cell growth/survival in serum-restricted conditions was limited to GFs and hormones, but not for the CDK4/6 inhibitor, Palbociclib (Fig. S3B), a commonly used therapeutic agent in metastatic ER+ breast cancers, which blocks the cell cycle transition from G1 to S by inhibiting the kinase activity of the Cyclin-dependent kinase (CDK)/cyclin complex.