Evaluation of angiogenesis in 77 pituitary adenomas using endoglin as a marker

Angiogenesis, a fundamental process for the development and growth of a tumor, is less expressive in adenomas than in the normal pituitary tissue. There is controversy about the behavior of angiogenesis as a function of hormonal secretion or other characteristics of pituitary tumors. Endoglin (CD105) is a proliferation-associated antigen on endothelial cells, as well as an endothelial progenitor cell marker. We used the anti-endoglin antibody, a glycoprotein expressed in endothelial cells and conjunctive tissue, as a new marker particularly associated with neovascularization, in order to determine microvascular density (MVD) in pituitary adenomas. There were 77 samples, 31 males and 46 females, carriers of micro- (n = 24) or macroadenomas (n = 53). No significant difference was found in MVD concerning the variables of age, clinical presentation, and immunohistochemical phenotype or tumor size. MVD in males (median 5.4) was significantly higher (P = 0.001) than in females (median 3.0). Cell proliferation, as evaluated by the MIB-1 antibody (a cellular proliferation index [Ki-67 antigen], which is present in all stages of the cellular cycle except for the resting cells), ranged from 0% to 19.58%. No correlation was found between MIB-1 and MVD. It is possible to infer that the lower MVD found in pituitary adenomas in females reflects an inhibitory estrogen action on TGF-beta1, a protein involved in vascular remodeling. Because of its role as a TGF receptor ligand, endoglin proved to be sensitive in detecting this gender difference in pituitary tumor angiogenesis.