title: Elevated levels of neutrophil gelatinase-associated lipocalin in bile from patients with malignant pancreatobiliary disease.
abstract: OBJECTIVE
  Accurate differentiation between benign and malignant causes of biliary obstruction remains challenging and reliable biomarkers are urgently needed. Bile is a potential source of such biomarkers. Our aim was to apply a proteomic approach to identify a potential biomarker in bile that differentiates between malignant and benign disease, and to assess its diagnostic accuracy. Neutrophil gelatinase-associated lipocalin (NGAL) is multi-functional protein, released from activated neutrophils, with roles in inflammation, immune function, and carcinogenesis. It has not previously been described in bile.
  
  
  METHODS
  Bile, urine, and serum were collected prospectively from 38 patients undergoing endoscopic retrograde cholangiopancreatography ("discovery" cohort); 22 had benign and 16 had malignant pancreatobiliary disease. Initially, label-free proteomics and immunoblotting were performed in samples from a subset of these patients. Enzyme-linked immunosorbent assay was then performed for NGAL as a potential biomarker on all samples in this cohort. The diagnostic performance of biliary NGAL was then validated in a second, independent group ("validation" cohort) of 21 patients with pancreatobiliary disease (benign n=14, malignant n=7).
  
  
  RESULTS
  NGAL levels were significantly raised in bile from the malignant disease group, compared with bile from the benign disease group in the discovery cohort (median 1,556 vs. 480 ng/ml, P=0.007). Biliary NGAL levels had a receiver operating characteristic area under curve of 0.76, sensitivity 94%, specificity 55%, positive predictive value 60%, and negative predictive value 92% for distinguishing malignant from benign causes. Biliary NGAL was independent of serum biochemistry and carbohydrate antigen 19-9 (CA 19-9) in differentiating between underlying benign and malignant disease. No significant differences in serum and urine NGAL levels were found between benign and malignant disease. Combining biliary NGAL and serum CA 19-9 improved diagnostic accuracy for malignancy (sensitivity 85%, specificity 82%, positive predictive value 79%, and negative predictive value 87%). The diagnostic accuracy of biliary NGAL was confirmed in the second independent validation cohort.
  
  
  CONCLUSIONS
  NGAL in bile is a novel potential biomarker to help distinguish benign from malignant biliary obstruction.
authors.affiliation: Hepatology and Gastroenterology Section, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, St Mary's Hospital Campus, London, UK.
authors.forename: Abigail A
authors.initials: AA
authors.lastname: Zabron
authors.forename: Verena M
authors.initials: VM
authors.lastname: Horneffer-van der Sluis
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Wadsworth
authors.forename: Fiona
authors.initials: F
authors.lastname: Laird
authors.forename: Magdalena
authors.initials: M
authors.lastname: Gierula
authors.forename: Andrew V
authors.initials: AV
authors.lastname: Thillainayagam
authors.forename: Panagiotis
authors.initials: P
authors.lastname: Vlavianos
authors.forename: David
authors.initials: D
authors.lastname: Westaby
authors.forename: Simon D
authors.initials: SD
authors.lastname: Taylor-Robinson
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Edwards
authors.forename: Shahid A
authors.initials: SA
authors.lastname: Khan
mesh_terms: D000209:Acute-Phase Proteins / Q000032:analysis / Q000378:metabolism*; D000328:Adult; D000368:Aged; D001646:Bile / Q000737:chemistry*; D001661:Biliary Tract Neoplasms / Q000150:complications / Q000378:metabolism* / Q000473:pathology*; D014408:Biomarkers, Tumor / Q000032:analysis / Q000378:metabolism*; D018395:CA-19-9 Antigen / Q000097:blood; D002779:Cholestasis / Q000209:etiology / Q000378:metabolism; D042882:Gallstones / Q000150:complications / Q000378:metabolism; D006801:Humans; D000071068:Lipocalin-2; D054834:Lipocalins / Q000032:analysis / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D010190:Pancreatic Neoplasms / Q000150:complications / Q000378:metabolism* / Q000473:pathology*; D010195:Pancreatitis / Q000150:complications / Q000378:metabolism; D011237:Predictive Value of Tests; D011446:Prospective Studies; D011518:Proto-Oncogene Proteins / Q000032:analysis / Q000378:metabolism*; D012372:ROC Curve; D012044:Regression Analysis
chemical_list: D000209:Acute-Phase Proteins; D014408:Biomarkers, Tumor; D018395:CA-19-9 Antigen; C489506:LCN2 protein, human; D000071068:Lipocalin-2; D054834:Lipocalins; D011518:Proto-Oncogene Proteins