Abstract LB-229: Utilizing a novel highly specific sialyl-Tn ELISA as a diagnostic for ovarian cancer (2019)

Abstract Sialyl-Thomsen-nouveau antigen (STn), a tumor-associated carbohydrate antigen (TACA) is elevated in several solid tumors. In ovarian cancer, increased STn levels correlate with chemo-resistance and decreased suvival. Our recent studies suggest that many of STn antibodies utilized previously were not as specific as originally proposed so through a proprietary platform, a highly specific anti-STn antibody with high binding affinity was developed. Subsequent study of this antibody as an antibody-drug conjugate (ADC) demonstrated reduced tumor growth in patient derived xenograft models of high grade serous OvCa, an effect that positively correlated with tumor STn levels. Collectively, these findings and those by others suggest that STn might serve as relevant OvCa therapeutic target and could play a role as a biomarker for discriminating malignant from benign ovarian tumors. In this investigation, we designed and optimized a custom ELISA to detect STn levels in human serum. Our objective was to determine whether we could distinguish between benign and malignant serum samples. The assay was employed on retrospective serum samples derived from patients diagnosed with benign gynecologic disease (n =62) and serum from patients diagnosed with high grade OvCa (n =200). Serum samples were all collected from consented patients under an approved IRB protocol. Based on our analysis, we determined the areas under the receiver operating characteristic curves (AUC of ROC) to compare how STn values associated with malignant or benign conditions. Our STn assay demonstrated an AUC of 0.74 at an STn value of 0.025. Of the 8 patients with malignancy and a CA-125 &lt; 35 mIU/ml, 6 were found to have elevated STn above the cutoff value and thus the sensitivity of CA-125 was significantly improved if elevated levels of STn were integrated as a biomarker. To determine whether circulating STn levels mirrored that which is detected in the tumor, we identified 15 samples with high (STn&gt;0.096) and 15 samples with low (&lt;0.096) levels and assessed STn in their matching formalin fixed, paraffin embedded tumor by immunohistochemistry (IHC). Elevated serum STn corresponded with positive STn focal 2+, 3+ staining 60% of the time while tumors with corresponding serum STn levels that were &lt;0.096 were associated with 6.7% IHC tumor low focal 0, 1+ staining) STn staining. There was staining in tumor samples of patients that had relatively low STn levels in the serum, which is not surprising since not all STn glycosylated proteins are shed into the blood. These data suggest that serum STn levels may improve the sensitivity of CA-125 alone to detect malignancy in an adnexal mass of unknown nature making it a valuable biomarker for clinical triage. Additionally, serum STn levels have a significant correlation (Fisher exact p&lt;0.01) with tumor expression and therefore may be useful in identifying women likely to respond to STn targeted agents. Citation Format: Linah F. Al-Alem, Jillian Prendergast, Justin Clark, Bianca Zarrella, Dan Dransfield, Whitfield Growdon, David Spriggs, Eric Eisenhauer, Jeff Behrens, Bo R. Rueda. Utilizing a novel highly specific sialyl-Tn ELISA as a diagnostic for ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-229.