MnSOD expression is less frequent in tumour cells of invasive breast carcinomas than in in situ carcinomas or non-neoplastic breast epithelial cells

Manganese superoxide dismutase (MnSOD) is an antioxidant enzyme capable of neutralizing superoxide anion molecules. In previous studies it has been su ggested to suppress both tumour proliferation and apoptosis. This study inv estigated 65 invasive, 50 in situ and 19 benign hyperplastic breast lesions for its immunohistochemical expression. MnSOD expression was also tested w ith in situ hybridization. To study cell proliferation, apoptosis and their association with MnSOD expression the neoplastic breast lesions were immun ostained with a monoclonal antibody to Ki-67 and the extent of apoptosis in them was determined by the TUNEL method. 32/65 (49%) of the invasive ducta l carcinomas, 41/50 (82%) of the in situ and 15/19 (79%) of the benign hype rplasias expressed the MnSOD protein. There were significantly more MnSOD p ositive cases in in situ carcinoma and in benign hyperplasia than in invasi ve carcinoma (p=0.00016 and p=0.022, respectively). Positivity was also mor e frequently found in non-neoplastic ductal and acinar epithelial cells tha n in invasive carcinoma. On the other hand, neoplastic epithelial cells of invasive and in situ carcinoma showed strong positivity more often than the epithelial cells of benign hyperplasia or non-neoplastic epithelium. In br east lesions, MnSOD positivity did not associate with proliferation or apop tosis. The lower frequency of MnSOD positive cases in invasive breast carci noma suggests that the lack of its expression might contribute to the devel opment of an invasive breast carcinoma phenotype and that it could in this way operate as a tumour suppressor gene, as previously suggested. Copyright (C) 2001 John Wiley & Sons, Ltd.