We found a trend toward a higher expression of mesenchymal markers such as ZEB1, N-cadherin, and TWIST, and lower expression of epithelial marker E-cadherin (Fig. 1I and Supplementary Fig. S1B) in cells with lower palbociclib activity (IC50 > 3.5 μM) among 11 HR+ breast cancer cell lines. Here, TWIST1 is linked to breast cancer.