Cathepsin D by western blotting and immunohistochemistry: failure to confirm correlations with prognosis in node-negative breast cancer.

PURPOSE: We attempted to replicate and improve on our previous study (N Engl J Med 322:297-302, 1990) that showed that 34-kd cathepsin D levels as determined by Western blotting strongly correlated with disease-free survival (DFS) and overall survival (OS) of axillary node-negative (N-) breast cancer patients. We also examined the prognostic significance of cathepsin D measured by immunohistochemistry (IHC) in these patients. PATIENTS AND METHODS: Western blotting was performed on cytosols from frozen tumor specimens of 927 N- breast cancer patients in the San Antonio Breast Tumor Bank. The monoclonal antibody M1G8 was used to detect cathepsin D (in previous study, a polyclonal antiserum had been used). The same monoclonal antibody was also used for frozen-section IHC staining of tumor specimens from 562 N- patients from the same tumor bank. Levels of cathepsin D expression were then correlated with DFS and OS.
RESULTS: Although the levels of cathepsin D expression as measured by Western blotting and IHC correlated with each other and with levels of cathepsin D measured in previous work using Western blotting with the polyclonal antiserum, in this present study, using the monoclonal antibody M1G8, we were unable to demonstrate that cathepsin D expression (measured by either Western blotting or by IHC) correlates with DFS or OS.
CONCLUSION: In this study, cathepsin D expression as determined by either Western blotting or IHC using the monoclonal antibody M1G8 failed to improve the prognostic evaluation of N- breast cancer patients. The role of cathepsin D expression as a prognostic factor is still not precisely defined, raising questions about its use in the routine evaluation of N- breast cancer patients.