RB1 and breast cancer: Next, we evaluated the expression and activation of key molecules of the three cellular signal pathways (ER, cyclin D/CDK4-6/Rb, and PI3K/AKT-mTOR) 72 h after treatment with the targeted inhibitors capivasertib, palbociclib, and fulvestrant in MCF-7, T47D, and ZR-75-1 breast cancer cell line models (Fig. 2E), as this is when immediate growth suppression induced by palbociclib is released22.