Overexpression of cyclin D1 is generally found in OR-α-positive, more differentiated breast cancer (Gillett et al, 1996; Michalides et al, 1996; Van Diest et al, 1997), whereas overexpression of cyclin A is associated with OR-α-negative, undifferentiated breast cancer (this study). This evidence concerns the gene CCND1 and breast carcinoma.