Quantitative immunohistochemical determination of cathepsin-D and its relation with other variables.

The expression of cathepsin D was evaluated by immunohistochemistry on histologic sections from formalin-fixed samples in a series of 436 primary breast cancers. The fraction of cathepsin D-positive tumor cells was not related to tumor size or hormone receptor status, and only weakly related to proliferative activity, evaluated as the 3H-thymidine labeling index. Conversely, a higher fraction of positive cells was observed in node-positive than in node-negative tumors (p = 0.05). A matched comparison between immunohistochemical and immunoradiometric results on individual tumors was carried out on 100 cases and showed a significant association but with a correlation coefficient of 0.46. The agreement of results from the two assays was higher in ER- than in ER+ tumors, which sometimes showed an immunostaining limited to macrophages and normal epithelial cells. In situ evaluation has the main advantage of being specifically applicable to detection in tumor cells and allows the simultaneous determination of different biologic aspects for a more complete understanding of breast cancer biology.