YAP1 and osteosarcoma: Since YAP/TAZ proteins translocate to the nucleus and act as transcriptional co-activators on TEADs or on other transcriptional factors such as RUNX2, the detection of YAP/TAZ in the nucleus by immunohistochemistry suggests that transcriptional activity of target genes that induce cell proliferation is activated in most high-grade osteosarcomas and could in part explain the poor prognostic value of this marker for PFS.