Azucena Esparís-Ogando from the Instituto de Investigación Biomédica de Salamanca (IBSAL), Spain, and colleagues showed that in a genetically engineered mouse model the activation of the MEK5 enzyme activates the ERK5 enzyme, a regulator of genes involved in cell proliferation, differentiation and survival, and promotes the development of soft-tissue sarcomas. This evidence concerns the gene MAPK7 and soft tissue sarcoma.