Nitric oxide is produced by several isoenzymes which are present in many different tissues. We have recently reported the presence of inducible nitric oxide synthase in a breast cancer cell line. The purpose of this study was to examine the distribution of endothelial nitric oxide synthase (eNOS) in a series of human breast tumours. Immunohistochemical investigations demonstrated immunolabelling of tumour cells with the primary antibody, bovine endothelial anti-nitric oxide synthase. Although there was no correlation between eNOS staining and tumour size, there was a significant (p < 0.005) negative correlation (ρ = –0.65) between the percentage of tumour cells staining positive for eNOS and the histologic grade of the tumour; there was also a significant (p < 0.05) negative correlation (ρ = –0.40) between the percentage of tumour cells staining positive for eNOS and the number of positive lymph nodes. A significant (p < 0.005) positive correlation (ρ = 0.63) between the percentage of tumour cells staining positive for eNOS and estrogen receptor (ER) expression by the tumour was also observed. In conclusion, our results demonstrate that eNOS is expressed by human breast tumours and that its presence negatively correlates with histologic grade and lymph node status and positively correlates with ER expression.

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