CYTOPLASMIC LOCALIZATION OF ENDOTHELIAL CONSTITUTIVE NITRIC-OXIDE SYNTHASE IN ENDOMETRIAL CARCINOMAS

Background: Production of nitric oxide by nitric oxide synthase (NOS) has been implicated in numerous physiologic and pathophysiologic proce sses including mutagenesis. This study was designed to examine the exp ression of the endothelial constitutive isoform of NOS (ecNOS) in endo metrial carcinomas. Methods: Fifty endometrial carcinomas (42 endometr ioid, 4 serous papillary, 2 clear cell, and 2 adenosquamous carcinomas ) and 21 normal endometrial gland tissue specimens (5 cases of prolife rative, 5 early secretory, 5 mid-secretory, and 5 late secretory and 1 menstrual phase endometrium), previously formalin fixed and paraffin embedded, were immunostained using a commercially available anti-ecNOS monoclonal antibody. Localization of ecNOS staining to the plasma mem brane, cytoplasm and nuclei was graded with respect to overall stainin g intensity (0-3+ scale) and frequency (percentage of immunoreactive c ells). Results: Relatively little staining for ecNOS was localized to the plasma membrane in either normal or neoplastic tissues. Normal and hyperplastic endometrial glands demonstrated moderate cytoplasmic and weak nuclear staining in a small percentage of cells. While ecNOS exp ression was most prominent in epithelial cells, weak expression was al so rarely noted in endometrial stroma, blood vessel walls, and endothe lium. We found a broad range of ecNOS expression in endometrial carcin omas, predominantly localized to the cytoplasm and nuclei. No statisti cally significant difference in ecNOS staining frequency or intensity was found between different histologic subtypes of endometrial carcino mas. No apparent correlation was found between ecNOS expression and tu mor stage, grade, extension to the lower uterine segment or cervix, no dal or distant metastases, recurrence, or final patient status among p atients with endometrioid adenocarcinomas. Endometrioid tumors invadin g more than 1/2 of myometrial thickness (n = 18) had significantly hig her cytoplasmic staining intensity than those tumors limited to the in ner 1/2 of myometrium (n = 27; 2.0 vs. 1.3, p < 0.04). Furthermore, a trend toward shorter disease-free survival was noted with increased st aining intensity and decreased staining frequency. Conclusions: Cytopl asmic and nuclear expression of ecNOS, which is primarily limited to t he glandular elements of normal endometrium, is also found to be expre ssed in endometrial carcinoma. Increased ecNOS staining intensity and decreased frequency tends to correlate with decreased disease-free sur vival. Lastly, increased cytoplasmic ecNOS staining intensity correlat es with increased myometrial invasion.