Localization of vascular endothelial growth factor and its receptors in digestive endocrine tumors: correlation with microvessel density and clinicopathologic features

Angiogenesis, a process related to tumor growth and malignancy, is stimulated by several growth factors. Among these is vascular endothelial growth factor (VEGF), which acts on endothelial cells by binding with 2 specific receptors, VEGFR1 and VEGFR2. Recent studies have demonstrated that VEGF expression is correlated with microvessel density (MVD) and tumor progression. Digestive endocrine tumors are heterogeneous neoplasms exhibiting variable biological aggressiveness and behavior that often are not predictable on morphologic grounds alone. The aims of this study were to evaluate the expression of VEGF, VEGFR1, and VEGFR2 in digestive endocrine tumors and to examine its correlation with MVD and malignancy. A total of 84 specimens from endocrine neoplasms and normal gut and pancreatic tissue were immunohistochemically studied using specific antibodies directed against VEGF, VEGFR1, VEGFR2, endothelial antigens, and gastroenteropancreatic hormones. Ultrastructural immunocytochemistry was performed to identify the cellular localization of VEGF and the VEGFRs. In normal tissues, VEGF immunoreactivity was detected in G cells and PP cells. Ultrastructurally, VEGF was localized within secretory granules. The VEGFRs were not significantly expressed by normal endocrine cells. VEGF-immunoreactive (IR) cells were detected in 40 of 83 tumors, mainly G cell and enterochromaffin cell neoplasms. VEGFR1-IR cells were found in 44 of 82 tumors, and VEGFR2-IR cells were found in 55 of 82 tumors, with no predilection for any specific tumor type. The expression of VEGF and its receptors did not correlate with MVD or malignancy. These results suggest that in normal tissues, endothelial functions may be regulated by VEGF produced by some endocrine cells and that a VEGF/VEGFR binding mechanism may be involved in tumorigenesis, but not in tumor progression and aggressiveness.