Xin Huang et al. applied single-cell sequencing to analyze the tumor microenvironment of recurrent osteosarcoma, identifying SERPINE1-expressing CAFs as a critical driver of tumor recurrence by promoting CAF activation, enhancing the epithelial-to-mesenchymal transition (EMT) process, and modulating macrophage polarization [35]. Here, SERPINE1 is linked to osteosarcoma.