Clinical evaluation of circulating serum sialyl Tn antigen levels in patients with epithelial ovarian cancer

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.