TET1 and breast cancer: Its role as a proto‐oncogene or an oncogene is contingent upon the downstream genes and signaling pathways regulated in that tumor.[33] For example, TET1 is a proto‐oncogene in T‐cell acute lymphoblastic leukemia (T‐ALL),[34] whereas it exhibits oncogene properties in acute myeloid leukemia (AML) and correlates with patients’ prognosis.[11] In breast cancer, TET1 exhibited a notable decrease in expression levels in tumors of estrogen‐pregnant hormone receptor‐positive patients.