ESR1 and cancer: To show that cancer cell viability in the ribociclib-induced growth arrested state is dependent on the EGFR pathway, we tested whether inhibitors of the EGFR pathway (other than Osimertinib and Gefetinib) affect viability of ERα-Mut cells treated either with vehicle, the SERD AZD-9496 (20 nM), or ribociclib (600 nM).