Abstract 3637: Ultrasensitive assays for combined detection of CEA+ extracellular vesicles and soluble CEA
Authors: Hebert Lucie , Al-Ameen Misk , Spriggs Talis , Nelson Collin , Gizzie Evan A. , Franklin Jeffrey L. , Coffey Robert J. , Routenberg David A. , Wohlstadter Jacob N. 
Published: March 2024

Abstract
Colorectal cancer (CRC) is the third most common cancer worldwide and is the second leading cause of cancer death in the United States. Carcinoembryonic antigen (CEA) is a biomarker commonly used in the management of CRC. It is typically present at low levels in the blood of healthy adults but is elevated in CRC samples and some other cancers. CEA is most commonly used to monitor treatment efficacy and as a critical part of post-treatment surveillance for residual disease, recurrence, and/or progression/metastasis. The CRC recurrence rate averages &gt;25%, and liver metastasis occurs in 25-30% of cases. Improved CEA assays could enable earlier determination of treatment failure, detection of lower levels of minimal residual disease (MRD) after treatment, or earlier detection of recurrence. CEA is a GPI-linked membrane protein secreted from CRC cells mainly by enzymatic cleavage of its GPI anchor. However, we have identified alternative secretion of CEA in association with extracellular vesicles (EVs). We hypothesized that the soluble CEA produced by canonical shedding and the alternatively secreted CEA may provide distinct information about the tumor or its microenvironment and serve as independent but complementary biomarkers of CRC. We developed ultrasensitive, multi-marker electrochemiluminescence (ECL) immunoassays for measuring intact EVs presenting CEA, CD73, or both in human plasma. We observed that plasma levels of CEA+EVs and CD73+EVs were elevated in some late-stage CRC samples compared to controls. CEA and CD73 double-positive EV (CEA+CD73+EVs) levels were also elevated in the same samples, exhibiting a 3-fold improved separation of these samples with CRC from controls, compared to detection of CEA+EVs. Additionally, approximately 25% of stage IV CRC samples had elevated CEA+EV and CEA+CD73+EV levels while exhibiting low soluble CEA. We confirmed this result in an independent sample set that included samples across all CRC stages, and also identified a few earlier-stage samples that exhibited high CEA+EVs and CEA+CD73+EVs without elevated soluble CEA. Since CEA+CD73+EVs and soluble CEA assays identified different subsets of samples, we combined the two assays into a single classifier for late stage CRC and controls, yielding improved receiver operator characteristic (ROC) with area under the curve (AUC) of 0.975 versus 0.927 for the standard soluble CEA assay or 0.788 for CEA+CD73+EVs alone. These results suggest that assaying EVs presenting multiple surface markers can increase specificity for the detection of tumor-derived EVs relative to a single marker and that assaying both soluble and EV-associated forms of CEA in plasma may improve the value of CEA measurement in CRC.
Citation Format: Lucie Hebert, Misk Al-Ameen, Talis Spriggs, Collin Nelson, Evan A. Gizzie, Jeffrey L. Franklin, Robert J. Coffey, David A. Routenberg, Jacob N. Wohlstadter. Ultrasensitive assays for combined detection of CEA+ extracellular vesicles and soluble CEA [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3637.