Manganese superoxide dismutase (MnSOD) is an important superoxide anion scavenger located in mitochondria and protects cells from the damage caused by reactive oxygen species. The oxygen balance has been reported to be related to the occurrence and invasiveness of malignant tumors. The aim of the current study was to elucidate the clinicopathological significance of immunohistochemical MnSOD expression in colorectal carcinoma. Consecutive 186 primary colorectal carcinomas which had been resected from 1987 to 1999 were examined for MnSOD expression by means of an immunohistochemical investigation. Sixty nine carcinomas (37.1%) had a positive response to MnSOD. The proportion of lymph node metastasis in MnSOD positive carcinomas (49.3%, 34 out of 69) was significantly higher than that in MnSOD negative carcinomas (26.5%, 31 out of 117; p=0.002). The proportion of patients classified to Dukes' stage A, B, C, and D in MnSOD positive carcinomas was 10.1, 33.3, 40.7, and 15.9%, respectively, and those were 23.1, 49.5, 24.8, and 2.6%, respectively in MnSOD negative carcinomas (p=0.0001). The survival rate in patients with MnSOD positive carcinomas was significantly worse than that in patients with MnSOD negative carcinomas (p=0.01). Multivariate analysis demonstrated that Dukes' stage of tumors was found to be a factor independently associated with prognosis of the patients. Our results showed that immunohistochemical expression of MnSOD can give auxiliary clinical information for malignant potential of colorectal carcinoma.

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