In another study by Calvani et al. in ES, the preliminary results showed the higher β3-AR expression in CD99+ cells (an antigen and marker of CTCs isolation and detection in ES [272]) in peripheral blood and cells from patients with metastasis or relapsed ones, suggesting a potential role of β3-AR as a predictive maker of disease or recurrence in both patients [273]. Here, CD99 is linked to Ewing sarcoma.