Relationship between Skp2 and p27 expression in 84 human breast carcinomas (sample set B). (a–f) Immunohistochemical stains for p27 (a, c, and e) and Skp2 (b, d, and f) of three breast carcinomas representative of the three patterns of Skp2/p27 expression. The carcinoma in the top row shows high p27 expression in both the residual normal duct in the center and in the infiltrating tumor surrounding it (a). Only one Skp2-positive cell is seen in the corresponding section in b. The tumor in the middle panel shows a p27-negative tumor (with positive residual normal ducts) (c). Strongly positive Skp2 tumor cells are seen in d. (e) Tumor that is negative for p27 (positive infiltrating lymphocytes are seen on the right). This tumor is also negative for Skp2 (f). (g) Graphic representation of the expression of Skp2 and p27 in the 84 tumors. Using the cutoffs (50% for p27 and 10% for Skp2) to define high and low expressors, tumors fall into three categories: high p27/low Skp2, low p27/high Skp2, and low p27/low Skp2.