Serum angiopoietin-like protein 2 as a novel biomarker of diagnosis and prognosis in gastric cancer.

Abstract

9 Background: Angiopoietin-like protein 2 (ANGPTL2) is a secreted glycoprotein with homology to the angiopoietins and is known to act as a causative mediator of chronic inflammation and inflammatory carcinogenesis. Recently, we demonstrated that ANGPTL2 overexpresses in gastric cancer (GC) compared to normal gastric mucosa and high ANGPTL2 is associated with poor prognosis. Therefore, if tumor-derived ANGPTL2 over-secretes systemically, focusing ANGPTL2 in blood is logical to evaluate its ability as a biomarker. Accordingly, we quantified serum ANGPTL2 level and assessed its clinical significance in GC patients. Methods: We screened serum ANGPTL2 levels from 32 GC and 24 normal controls (NC) by ELISA (cohort 1). Next, we validated 194 serum samples from GC and 48 NC (cohort 2). Finally, we examined ANGPL2 expression in matched GC tissues of cohort 2 (n=194) by immunohistochemistry (IHC). The IHC score of ANGPTL2 was determined on the basis of both staining intensity and the percentage of positive cells. Results: In cohort 1,serum ANGPTL2 levels in GC were significantly higher than that in NC (p<0.05). Serum ANGPTL2 differentiated GC from NC with high accuracy (AUC=0.814). Analysis of cohort 2 also indicated that serum ANGPTL2 levels in GC were significantly higher compared to NC (p<0.0001), and increased according to UICC stage progression. In addition, serum ANGPTL2 had a promising AUC (0.831) with high sensitivity (73.0%) and specificity(82.2%) to distinguish GC from NC. High serum ANGPTL2 was significantly associated with lymphatic invasion (p=0.03), vessel invasion (p=0.02), distant metastases (p=0.0002), early recurrence (p=0.004) and poor survival (p=0.01), consequently emerged as an independent predicting recurrence marker (HR=5.06, p=0.0004) and prognostic marker (HR=3.6, p=0.01) in GC. Of interest, ANGPTL2 levels in serum from GC patients closely correlated with IHC scores of cytoplasmic ANGPTL2 at the invasive margin of matched GC tissues (r= 0.16, p=0.02). Conclusions: Serum ANGPTL2 levels, which might be secreted from primary or metastatic site into blood stream, have extremely strong potential as a novel biomarker for diagnosis, predicting recurrence and poor prognosis in GC patients.