TET1 and breast cancer: A case in point is that a novel circular RNA consisting of exons 4–2-3 of the friend leukemia virus integration 1 (FLI1) gene, referred to as FECR1, could recruit ten-eleven translocation methylcytosine dioxygenase 1 (TET1), a demethylase that is actively involved in DNA demethylation, to the promoter region of its host FLI1 gene, leading to DNA hypomethylation of CpG islands and active cis transcription of the FLI1 gene, thus regulating the metastasis of breast cancer cells [50].