Background: The clinical significance of pyrimidine nucleoside phosphorylase (PyNPase) activity in breast carcinomas has never been determined. Materials and methods: In 41 cases of breast carcinoma, the enzyme activity of PyNPase was determined by the high performance liquid chromatography (HPLC) assay and its value was analyzed with clinicopathologic variables. The expression level of mRNA was examined by the semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) assay and compared with the enzyme activity. Results: The higher activity of PyNPase was significantly correlated not only with the presence of vascular permeation (P = 0.02) but of lymph node metastasis (P = 0.02). The mRNA expression correlated well with the enzyme activity (r = 0.74, P < 0.01). A multivariate analysis disclosed the PyNPase factor to be associated with lymph node metastasis. In addition, 17 (41%) showed positive staining only in the tumor stromal cells and 18 (44%) cases showed positive staining in both the tumor stromal cells and the carcinoma cells by immunohistochemical study. Conclusions: These findings suggest that PyNPase activity is a new marker predicting the malignant potential of breast carcinomas, especially with respect to lymph node metastasis, and that the RT-PCR assay is a more useful method than direct evaluation of PyNPase activity.
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