To examine the status of Cyclin D1 expression in these tamoxifen-resistant models, quantitative PCR (qPCR) and western blotting was done to compare the mRNA and protein levels of Cyclin D1 between parental (MCF7-Pa and T47D-Pa) and resistant (MCF7-Re and T47D-Re) breast cancer cells. The gene discussed is CCND1; the disease is breast carcinoma.