Expression of Tn Antigen in Tumors and Transitional Margins of Colorectal Cancer
*Gabrielle E Dombek
BIDMC, Boston, MA
Objective: Alterations in O-linked glycans in colorectal cancer (CRC) and expression of the tumor antigen Tn antigen have been reported in CRCs and have been correlated with tumor progression, metastasis, and poor prognosis. Detailed immunohistochemical (IHC) analysis of Tn expression and identification of the glycoproteins on which Tn is observed using well-defined monoclonal antibodies have not been reported and are our aims. Design: IHC staining using ReBaGs6, a recombinant murine IgM with high specificity for Tn, was performed in discarded surgical specimens. Samples were obtained from CRC, tumor-adjacent transitional margin, and normal tissue >3cm away. Immunoprecipitation and LC-MS/MSn were used to characterize the proteins on which Tn is expressed.Setting/Patients: Adult patients with biopsy-proven CRC at BIDMC undergoing surgical resection
Interventions: Tissues were obtained from discarded surgical specimens
Main Outcome Measures: H-scores, Glycoproteins
Results: IHC results (Figure 1) reveal low intracellular Tn staining in distant normal mucosa but high expression in both transitional margin and CRC. Transitional margin demonstrates a Tn expression level elevated relative to CRC. Proteomic analysis in tissue homogenates from 6 patients identified the following Tn-expressing glycoproteins in either CRC or transitional margin but not in distant normal tissue: Histone cluster 1 H1 family member b, Myoferlin, Vesicle amine transport 1, and Chaperonin containing TCP1 subunit 3.
Conclusions: The expression of Tn antigen in the transitional margin exceeds that of the CRC itself. CRC transitional margin mucosa, in addition to CRC itself, represents a source of glycoproteins rich in Tn that may offer future biomarker targets. 
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