Differential Expression of Cyclin D1 in Breast Papillary Carcinomas and Benign Papillomas

Abstract Objectives.—Distinguishing intraductal papilloma from papillary carcinoma of the breast can be difficult using histologic criteria. Since cyclin D1, a G1 cell-cycle regulatory protein, is detectable immunohistochemically in a subset of breast carcinomas but not in benign breast tissues, we hypothesized that cyclin D1 immunoreactivity may be a marker for identifying papillary carcinoma. Methods.—Using an immunohistochemical method, we assessed for cyclin D1 expression in 8 breast papillomas and 6 papillary carcinomas, all of which were formalin fixed, routinely processed, and paraffin embedded. Cyclin D1 positivity also was compared with the overall proliferation rate, which was assessed by using the proliferation marker Ki-67. In each case, a 200-cell count was performed to obtain the percentage of cells positive for these 2 markers. Results.—The percentage of cyclin D1–positive cells was significantly higher in papillary carcinomas (89% ± 18%; range, 53%–98%) than in papillomas (8% ± 7%; range, ...