Cyclin D1 is one of the most important cell cycle regulators in the G1 to S phases and is overexpressed in various cancers, such as breast cancer,1, 2 non-small-cell lung cancer,1, 3 melanoma,4 pancreatic cancer5 and colorectal cancer.6 The causative mechanisms of cyclin D1 overexpression are intricate and diverse at each of the transcriptional, translational and posttranslational levels. The gene discussed is CCND1; the disease is breast cancer.