Evaluation of cathepsin D as a prognostic factor in breast cancer.

The biologic rationale for the importance of cathepsin D in breast cancer is a provocative one. Cathepsin D is both an estrogen inducible and a constitutively produced protease, which may also act directly as a peptide growth factor. Thus it may play a role in tumor invasiveness, and also in driving cell proliferation. Reported clinical studies are conflicting, with some studies showing cathepsin D levels to correlate with clinical outcome, and other studies finding prognostic significance only in selected subsets of patients, if any. Thus cathepsin D is a potentially important prognostic marker whose clinical application awaits further definition.