EWSR1 and Ewing sarcoma: Fluctuating expression of the transcription factor EWSR1-FLI1, for example, is reported to be a major source of phenotype plasticity in Ewing sarcoma cells, where EWSR1-FLI1high states are characterized by active cell proliferation and EWSR1-FLI1low states by invasion and metastasis (Franzetti et al., 2017).