Cathepsin D as a prognostic indicator for node-negative breast cancer patients using both immunoassays and enzymatic assays

Abstract

This is a retrospective study on 162 node-negative patients, with both biochemical and clinical factors being measured for determination of prognostic markers. Steroid receptors were measured on all tumors, while tumor size, histological grade, ploidy status, and cell cycle kinetics indicators could not be found or measured on 25 or less of the patient group. The primary focus of this study was the measurement of cathepsin D, analyzed by two different procedures, and 161 of the 162 patients had at least one value. The antigenic assay was performed using the US-CIS kit, and it was sensitive and reproducible. A biochemical assay using the enzymatic activity of cathepsin D was developed, and it gave proportional values, compared to the antigenic assay values (r2 = 0.79). Our results indicated that the mean antigenic levels were 20% higher than the biochemical assay levels (P = 0.001). High levels of cathepsin D by the antigenic assay predicted poor relapse-free (P = 0.0001) and overall (P = 0.0004) survival. High levels of cathepsin D by the biochemical assay also predicted poor relapse-free (P = 0.031) and overall (P = 0.0013) survival. The cathepsin D values were still useful as predictors of outcome after multivariate analysis. Several other factors, such as grade and S phase, were useful as additional prognostic indicators. In conclusion, cathepsin D is the most useful marker in node-negative patients, and the analysis can be performed by both a biochemical and an antigenic assay.