YAP1 and neoplasm: Finally, because CMS4 tumours are characterized by high stromal, most notably fibroblast, infiltration [3], it is tempting to speculate that YAP/TAZ activation in CMS4 tumours cells may also be, at least partly, driven by signals emanating from the tumour microenvironment such as PGE2 [37,74] (see Figure 6).