Relation between cathepsin D expression and other prognostic factors in breast carcinomas.

We evaluated cathepsin D concentrations in 318 breast carcinoma specimens with a standardized IRMA and established distribution values of 5.9-217.8 nmol/g (median 51.8). Concentrations of cathepsin D did not correlate with age or with concentrations of HER-2/neu oncoprotein, estrogen receptor, or epidermal growth factor receptors. A significant correlation was observed between cathepsin D and progestin receptor (P = 0.009), but only in postmenopausal patients. In our role as a National Reference Laboratory for conducting interlaboratory comparisons of tumor markers, we evaluated cathepsin D assay proficiency by using control samples with intra- and interassay CVs of 2-8% and 10-13%, respectively. Human reference specimens containing known quantities of cathepsin D were developed to facilitate standardized testing. The IRMA procedure and the use of quality-assurance samples permits evaluation of the clinical significance of cathepsin D in human breast cancer trials.