Context .- Progression of retinoblastoma is associated with increased tumor angiogenesis. However, a clear relationship between the expression of angiogenic markers in specific regions of the tumor and tumor progression has not been established. This study investigates the association between angiogenic factors in retinoblastomas with choroidal and/or optic nerve invasion (high-risk/invasive retinoblastoma) and expression of Sox2, a stem cell marker. Objective .- To investigate the association between the expression of angiogenic factors and markers of tumor invasiveness, such as the stem cell marker Sox2, in retinoblastoma tissues. Design .- Immunohistochemistry was used to evaluate coexpression of the angiogenic growth factors vascular endothelial growth factor A (VEGF-A), VEGF receptor 2 (VEGFR-2), and endoglin (CD105); markers of glial differentiation (vimentin and glial fibrillary acidic protein); and a neural stem cell marker (Sox2). Expression was assessed in nonneoplastic and neoplastic ocular tissues collected from enucleated eyes of patients with retinoblastoma. During qualitative data interpretation, evaluating pathologists were masked to patient grouping. Results .- Expression of VEGF-A and VEGFR-2 in noninvasive (non-high-risk feature) retinoblastoma tumors was lower than in the invasive, or high-risk feature tumors. Moreover, our data indicate that the tumor cells, and not the surrounding stroma, secrete VEGF-A and that angiogenesis is mostly localized to the iris. Finally, our data showed that the expression of the neural stem cell marker Sox2 is associated with eyes with increased VEGF-A expression and tumor invasiveness. Conclusions .- Increased expression of angiogenic factors, with a concomitant increase in expression of the stem cell marker Sox2 observed in retinoblastoma tissues, may partially explain the aggressiveness of these tumors. The complex interaction of angiogenic and stem cell-related pathways in these tumors, especially in high-risk feature retinoblastoma, suggests that targeting tumor cells capable of secreting vasculogenic factors, as well as proangiogenic genes and signaling pathways, may be necessary for development of effective antimetastatic retinoblastoma drugs.