α1-Acid Glycoprotein with Highly Fucosylated Glycans as a Potential Diagnostic Marker for Early Detection of Hepatobiliary and Pancreatic Cancers

Abstract

Background: Previously, we reported elevated levels of fucosylated α₁-acid glycoprotein (fAGP) in plasma samples from patients with diverse types of cancers. Accordingly, fAGP was assumed to be a potential biomarker for the early detection of cancers. Methods: The fAGP level was retrospectively measured in preoperative plasma samples from 213 patients with either hepatic, biliary tract, or pancreatic cancer and was analyzed together with levels of six existing tumor markers determined as reference standards. Results: When the cutoff value was set at 25.45 U/μg, elevated levels of fAGP were significantly observed in cancer patients. The sensitivity, specificity, and accuracy for the detection of malignancy in these diseases were determined to be 70.79, 51.72, and 68.12, respectively. In contrast, all the tumor markers exhibited low sensitivity and accuracy, even though they commonly had extremely high (≥80%) specificity. Further, a significant number of patients in both early and advanced clinical stages were found to be false negative in these tumor makers but were found to be positive in the fAGP level. A dramatic improvement in the diagnosis by tumor markers in such patients with all clinical stages was found by the determination of the fAGP level. This indicated that fAGP could serve to correct false-negative diagnosis with tumor markers. Conclusions: It is believed that fAGP could be a relevant, unique, and highly sensitive biomarker for early diagnosis of hepatobiliary and pancreatic cancers.

Keywords: combination assay; early diagnosis of cancer; fucosylated glycans; sensitivity; tumor biomarker; α1-acid glycoprotein.

Figure 1

Branched N-linked glycans in α₁-acid glycoprotein (AGP). One mole of AGP possesses 5 glycan chains including di-, tri-, and tetra-antennary glycan chains. Highly fucosylated AGP found in cancer patients were determined to be synthesized mainly on the tetra-antennary glycan chains accompanied by extremely elevated amounts of such glycan chains [22,23]. The presence of repeated lactosamine structures with Le^X structure (Galβ1,4[Fucα1,3]GlcNAc) in the tetra-antennary chains was predicted at the position of the black triangle in cancer patients. NeuAc, N-acetylneuraminic acid; Gal, d-galactose; GlcNAc, N-acetyl-d-glucosamine; Man, d-mannose; Fuc, l-fucose; and Asn, asparagine.

Figure 2

Positive rates of fAGP and respective tumor markers in plasma samples from patients with either hepatic, biliary tract, or pancreatic cancer. The total numbers of the patients examined were as follows: fAGP (178), CA19-9 (168), DUPAN-2 (122), SPan-1 (122), CEA (168), AFP (78), and PIVKA-II (67) (top). The positive rates were also determined depending on their clinical stages, such as in the early (stages 0–1) (middle) and advanced (stages 2–4) (bottom) stages, respectively.

Figure 3

Positive rates of fAGP and respective tumor markers in plasma samples from patients with hepatic, biliary tract, and pancreatic cancer. White and gray bars (top, middle, and bottom) indicate corresponding positive rates in patients in the early (stages 0–1) and advanced (stages 2–4) stages, respectively. n.t. = not tested; (0) = no samples tested.

Figure 4

Diagnostic results of all patients were displayed as a set of levels of both respective tumor markers and fAGP, concurrently measured. Each symbol was plotted based on a set of levels of the tumor markers (horizontal axes) and fAGP (vertical axes). Four quadrants were defined by two axes lined at two cutoff values of the tumor markers (indicated) and fAGP (25.45 U/mg). Each quadrant includes patients who possess fAGP (−) and the tumor marker (−) (A), fAGP (−) and the tumor marker (+) (B), fAGP (+) and the tumor marker (−) (C, gray screen), and fAGP (+) and the tumor marker (+) (D), respectively. White and black circles indicate patients with early (stages 0–1) and advanced (stages 2–4) stages, respectively. Numbers of patients were as follows: in CA19-9/fAGP (168 with 52 early and 116 advanced stages), in DUPAN-2/fAGP (122 with 31 early and 91 advanced stages), in SPan-1/fAGP (122 with 31 early and 91 advanced stages), in CEA/fAGP (168 with 52 early and 116 advanced stages), in AFP/fAGP (78 with 28 early and 50 advanced stages), and in PIVKA-II/fAGP (67 with 26 early and 41 advanced stages).