CDK4 and breast cancer: Despite a close interplay of the involved pathways, there are increasing numbers of reports indicating that tamoxifen [160], epirubicin [161], doxorubicin [157,162], paclitaxel [163], and even the novel CDK4/6 inhibitor palbociclib [134,164] induced autophagic flux in parental and drug-resistant ER+ and TNBC cells. Knocking down key autophagy genes (ATG5, BECN1, or ATG7) in combination with TAM treatment resulted in decreased cell viability in MCF7 and T47D breast cancer cell lines.