Furthermore, when analyzing the association of palbociclib activity and PLK1 mRNA expression in 38 breast cancer cell lines using Cancer Cell Line Encyclopedia (CCLE) data, the current study found that cells with low palbociclib activity (IC50 > 500 nM) had higher PLK1 expression (p = 0.006; Figure 4B). This evidence concerns the gene PLK1 and breast cancer.