Correlation between Skp2 and proliferative index in sample set B. (a–d) Immunohistochemical stains of two representative breast carcinomas with anti-Skp2 (a and c) and anti-Ki67 (b and d) Ab’s. The tumor in the top row shows high Skp2/high Ki-67 levels. The one in the bottom row displays low Skp2/low Ki67 levels. (e) Graphic representation of the direct correlation between Skp2 expression and proliferative index in the 37 breast carcinomas. (f–k) Dual immunofluorescence of Skp2 with Ki67 in the breast cancer cell line MCF7 and in breast carcinomas. In MCF-7 cells (f, g, and h) as well as in breast carcinoma samples (i, j, and k), Skp2 protein (Texas Red) was detected only in cells expressing Ki67 (FITC). Both Ki67 and Skp2 are localized in the nucleus. A subset of cells that expressed Ki67 protein was negative for Skp2 expression (h and k).