Endostatin is a negative regulator of angiogenesis. We examined plasma endostatin levels (PESLs) in cancer patients and healthy controls. PESLs were detected by competitive enzyme immunoassay in 147 patients with primary breast cancer, 44 patients with other histological types of cancer, 26 patients with recurrent breast cancer, 17 patients with benign breast disease and 221 healthy controls. PESLs were elevated in those patients with cancer or benign breast disease. In patients with primary breast cancer, significantly higher PESLs were found in post-menopausal patients than in pre-menopausal patients (p<0.01), although there were no differences in the other clinicopathological characteristics evaluated. PESLs in primary breast cancer patients did not change after surgery, but they increased after administration of the adjuvant tamoxifen. When we applied an age-matched cut-off value as a mean of the values for the female controls, we found that node-negative breast cancer patients with high PESLs had a significantly more favorable relapse-free survival time than those with low PESLs (p<0.05, log-rank test). Our data demonstrate that PESLs are detectable in healthy controls, and that cancer patients have elevated PESLs. A larger study is warranted to clarify the clinical significance of circulating endostatin.

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