OBJECTIVE Previous epidemiologic studies have demonstrated that nonsteroidal anti-inflammatory drugs can reduce the risk of breast cancer, and this possibly happens via cyclooxygenase (COX) inhibition. Moreover, growth factor-inducible COX-2, which is overexpressed in neoplastic tissue, is an attractive therapeutic target. Thus, we evaluated the expression of COX-2 in breast cancer tissues, and we assessed the association between COX-2 expression and HER-2/neu expression and also with several clinicopathological features. METHODS We analyzed the surgical specimens from 112 women with breast cancer who had undergone lumpectomy or mastectomy. The expressions of COX-2, HER-2/neu, MMP-2 and TIMP-2 were determined immunohistochemically. The correlations between COX-2 expression and several variables, including clinicopathological factors, HER-2/neu expression, MMP-2 expression and TIMP-2 expression were analyzed. Survival analysis was also performed with respect to COX-2 overexpression. RESULTS The overexpression of COX-2 protein was observed in 28.6% of the breast cancer tissues. Tumors with lymph node metastasis more frequently showed COX-2 overexpression than did those tumors without metastasis (p=0.039), and the increased COX-2 expression correlated positively with HER-2/neu overexpression (p=0.000). No significant differences were found for the MMP-2 or TIMP-2 expression rates in the COX-2 positive and negative groups. The survival analysis revealed no significant differences according to the COX-2 expression. CONCLUSIONS This study results suggest that increased COX-2 expression is related with the progression of breast cancer, e.g., with lymph node invasion. COX-2 overexpression found to be related with HER-2/neu overexpression, but not with MMP-2 or TIMP-2 expression. These results support the potential use of selective agents that inhibit COX-2 or HER-2/neu for the management of breast cancer.