Fitness measurements were well correlated between biological replicates (Pearson’s r = 0.996) and across the three breast cancer cell lines (r = 0.922 to 0.937), with CDK1 ranking as the most deleterious knockout, consistent with its role as a master regulator of cell-cycle progression32,59 (Fig. 2a, Extended Suppl. This evidence concerns the gene CDK1 and breast cancer.