This study used Western blot analysis to measure the expression of superoxide dismutases (Mn-SOD and Cu/Zn-SOD) in breast cancer tissues from 57 patients. Mn-SOD expression in the breast cancer tissues averaged 1.5-fold higher than in the adjacent tumor-free tissues (p <0.05). There was no significant difference in Cu/Zn-SOD expression between neoplastic and tumor-free breast tissues. This study shows a significant increase of Mn-SOD expression in breast cancer tissues. The authors speculate that up-regulation of Mn-SOD expression induced by oxidative stress or local inflammation may contribute a selective growth advantage to tumor cells compared to their normal counterparts.