Cathepsin D (CD) is a lysosomal protease that can be used as an important prognostic cytosolic factor for breast cancer. Its over-expression in breast cancer cells and in the host stromal cells in the tumor has been proposed as being a poor prognostic indicator. However, its prognostic value is still being debated. Therefore, CD expression needs to be examined in more relevant subsets of tissue in order to refine its prognostic significance and the clinical applications.

Regardless of the lymph node status, 110 T1 invasive ductal carcinomas of the breast were immunohistochemically evaluated for the CD expression using rabbit anti-cathepsin D monoclonal antibody. This study separately assessed the expression of CD in the invasive component (lDC). in the in situ component (DClS), and in the juxtatu-moral stromal cells (JTSC). The CD expression level in these three kinds of tissues were correlated with the nuclear grade, ER. PR, c-erb-B2, p53. the N stage, the T stage, and the 5 year metastasis-free survival.

Positive CD expression in the JTSC was associated with the T stage (p = 0.001) and the N stage (p = 0.029), whereas positive CD expression in the DClS and IDC was not. In addition, strong CD expression in the JTSC correlated with the nuclear grade of the invasive component (p = 0.024). In all three components, no statistically significant correlation was found between the biomarker (ER, PR, cerb-B2. p53) and the CD expression. On univariate analysis, positive expression in the JTSC was correlated with a poor 5 year-metastasis free survival (p = 0.007), but the positive expression in the IDC and DCIS was not.

CD expression of the JTSC could represent the N stage, the T stage, and the nuclear grade of T1 IDC. Whether or not it would have an independent influence on the prognosis of T110C, CD expression in the JTSC is probably an indicator of the tumor virulence. CD expression in the JTSC will provide an important clue for the development of new CD targeted therapies, and it will serve as an important criterion for selecting the appropriate candidates for these future targeted therapies.