Introduction & Objective: The breast cancer is the most common malignancy in women even according to the new studies this is concluded that the breast cancer in women is the most essential and important oncology’s disease .This malignancy is a suitable example of the use of biologic markers to learn more about prediction, incidence, diagnosis, treatment and outcome .One of this markers is cathepsin D. It is an aspartatic lysosomal protease that playes main role in multiple tumor progression stages. The purpose of this study was to determine the frequency of expression of cathepsin D in primary breast cancer and it’s correlation with axillary lymph nodes involvement, grade and stage of tumor.

Materials & Methods: The study was a cross-sectional one that was performed on 75 samples from patients with breast cancer who admitted in Mostafa Khomeiny Hospital (2000-2004). After preparing the samples, a tissue section from each sample was obtained. One of the tumoral and lymph nodes sections were stained by H&E. We determined the type of tumor, the number of lymph nodes, the stage and the grade of the tumor. Cathepsin D assessed by a immunohistochemical technique using a monoclonal antibody.

Results: Our study showed 68% of samples were positive for cathepsin D.70.7% of patients had lymph nodes involvement. The most of patients were in stage II (57.3%) and 42.7% were in grade II. In this study, we did not find any correlation between cathepsin D expression and the studied factors.

Conclusion: According to the results of previous studies and our study, it seems we require to more complete studies with more specimens and long-term follow up to understand exact role of cathepsin D in breast cancer prognosis.