ESR1 and Ewing sarcoma: Interestingly, PRC1 is co-recruited with oncogenic transcription factors (TFs) to active enhancers in estrogen receptor positive (ER+), triple-negative breast cancer (TNBC), leukemia, hepatocellular carcinoma cell lines and Ewing sarcomas (Chan et al., 2018; Sánchez-Molina et al., 2020).