Although a trend of increased CD31 expression was observed as osteosarcoma progressed, no significant differences were found between different pathological stages in terms of CD31 density (Figure 3), suggesting that vascularity (represented by the expression of CD31) was not dramatically altered during the pathological progression of nonmetastatic osteosarcoma, a scenario different from metastatic groups. The gene discussed is PECAM1; the disease is osteosarcoma.