Cyclin D1 expression has previously been shown to correlate strongly to ER positivity and deregulation of cyclin D1 has been associated with resistance to endocrine therapy in breast cancer cell lines [5, 6], while the role of cyclin D1 overexpression and endocrine resistance in the clinic is still controversial [5, 7–12]. The gene discussed is CCND1; the disease is breast carcinoma.