Several in vitro studies have shown that nitric oxide (NO) produced by NO synthase (NOS), such as inducible NOS (iNOS) play an important role in tumor biology. We immunohistochemically examined the expression of iNOS and p53 proteins in patients with transitional cell carcinoma (TCC) of the urinary tract, including adjacent dysplastic lesions to determine the significance of the tumor behavior. Of total 94 tumors, in the present study, 41 (43.6%) tumors exhibited homogeneous immunostaining (diffuse strong positivity in tumor cells, >60%) and 53 (56.4%) tumors heterogeneous staining (variable positivity in tumor cells, 20-60%). No TCCs exhibited negative iNOS immunostaining was found. Thirty (31.9%) of 94 TCCs were positive with anti-p53 antibody, including 23 of homogeneous and 7 of heterogeneous staining. Of 23 TCCs with homogeneous p53 immunostaining, 11 tumors exhibited homogeneous iNOS immunoreaction. In the present study, dysplastic lesions adjacent to carcinomas were detected in 64 cases including 36 TCCs with homogeneous iNOS expression. All dysplastic lesions adjacent to the 36 TCCs with homogeneous iNOS immunostaining exhibited homogeneous iNOS immunostaining. No significant association between iNOS immunoreactivity and any clinicopathological factors as well as p53 immuno-reactivity were found. These in vivo findings provide evidence for frequent iNOS protein expression in TCC. In addition, our observations indicate that overexpression of iNOS expression may be one of the early events in the carcinogenesis of TCC.

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