S100A8 and osteosarcoma: Unsupervised consensus clustering of osteosarcoma patients based on the levels of eight identified soluble immune checkpoint proteins (CD48, B7-H2, TIMD-4, B7-H6, CD134, B7-H5, CD47, S100A8/A9) classified patients into two clusters (Figure 2A, Supplementary Figure 2, k = 2): 31 in cluster 1 and 36 in cluster 2.