T47D-Y cells, the parental cells of the YA, YB, and Y-AR breast cancer cells, were found to contain little GR mRNA based on microarray data and exhibited no transcriptional activity when treated with dexamethasone (data not shown), allowing us to conclude that the activity of MPA in breast cancer cells occurs through PR and AR and not through GR. The gene discussed is PGR; the disease is breast cancer.