It has been reported that lovastatin and simvastatin in their prodrug form (β-lactone) inhibit the chymotrypsin-like activity of proteasomes, leading to the accumulation of cyclin-dependent kinase (CDK) inhibitors p21 and p27 (p21Cip1 and p27Kip1) and subsequent G1 arrest in breast cancer cell lines [176,177]. The gene discussed is CDKN1B; the disease is breast carcinoma.