Decreased alpha-1,4-linked N-acetylglucosamine glycosylation in biliary tract cancer progression from biliary intraepithelial neoplasia to invasive adenocarcinoma

Biliary tract cancer (BTC) is typically lethal due to the difficulty of early stage diagnosis. Thus, novel biomarkers of BTC precursors are necessary. Biliary intraepithelial neoplasia (BilIN) is a major precursor of BTC and is classified as low or high grade based on cell atypia. In normal gastric mucosa, gastric gland mucin-specificO-glycans are unique in having alpha 1,4-linkedN-acetylglucosamine (alpha GlcNAc) attached to MUC6. Previously, we reported that alpha GlcNAc functions as a tumor suppressor of differentiated-type gastric adenocarcinoma and that decreased alpha GlcNAc glycosylation on MUC6 in gastric, pancreatic, and uterine cervical neoplasms occurs in cancer as well as in their precursor lesions. However, alpha GlcNAc and MUC6 expression patterns in biliary tract neoplasms have remained unclear. Here, we analyzed MUC5AC, MUC6, and alpha GlcNAc expression status in 51 BTC cases and compared the expression of each with progression from low-grade BilIN to invasive adenocarcinoma (IAC). The frequency of alpha GlcNAc-positive and MUC6-positive lesions decreased with tumor progression. When we compared each marker's expression level with tumor progression, we found that the MUC6 expression score in IAC was significantly lower than in low-grade or high-grade BilIN (P P < 0.01, respectively). However, the alpha GlcNAc expression score was low irrespective of histological grade, and also lower than that of MUC6 across all histological grades (P < 0.001 for low-grade and high-grade BilIN, andP < 0.01 for IAC). These results suggest that decreased expression of alpha GlcNAc relative to MUC6 marks the initiation of BTC progression.