Sialyl Tn antigen (NeuAc alpha 2----6GalNac alpha 1----0-Ser/Thr [STN]) with
antigenic specificity in the core structure of
mucin-type
carbohydrate chains has been determined. In the present study, we evaluated the clinical significance of this new
carbohydrate antigen, STN, in patients with
epithelial ovarian cancer. With the use of a radioimmunoassay developed to detect STN
antigen in serum, elevated (greater than or equal to 32.6 U/mL)
antigen levels were observed in 50.0% of patients with
ovarian cancer. In contrast, 3.8% of healthy individuals had STN
antigen levels greater than or equal to 32.6 U/mL. In 9.6% of patients with benign
gynecologic diseases and 0% of pregnant women, there were elevated levels of STN
antigen. There was a significant difference (P less than .001) in STN
antigen levels between patients with
ovarian cancer and patients with benign
gynecologic diseases, pregnant women, or the controls. The mean +/- SD for all evaluated samples of
ovarian cancer was 109.2 +/- 146.8 U/mL. Both the mean values and the positive rate increased as the stage advanced. Classified according to the histologic type, the highest positive rate (61.0%) was observed in
mucinous adenocarcinoma. The usefulness of STN
antigen as a circulating
tumor marker in
ovarian cancer was estimated as follows: sensitivity 50.0%, specificity 93.5%, positive predictive value 72.2%, negative predictive value 84.7%, and diagnostic value 46.8%. Serum STN
antigen levels were elevated in 12 of 33 patients with
ovarian cancer who had serum
CA 125 antigen levels less than 35 U/mL. While
CA 125 antigen levels were elevated in 74.6% and STN
antigen levels were elevated in 50.0% of the same population, the use of both assays indicated the sensitivity of detection of 83.8% in the population studied.