CDK5 and breast cancer: Moreover, we found that the expression of Cdk5 activator p35 and ADD1 were much higher in metastatic breast cancer cells MDA-MB-231 than in non-metastatic breast cancer cells MCF7 (Fig. 7a), suggesting that aberrant expression of Cdk5 and/or its activator p35 as well as elevated ADD1 phosphorylation at T724 may serve as biomarkers for prognosis of breast cancers.