TET1 and breast cancer: Notably, loss-of-function TET2 mutations are frequent in leukemia, [11, 12] but much low mutation rate has been observed in HCC (< 5%).13 Although all three TETs are considered to be tumor suppressors in various cancers, evidence is emerging that TET1 and TET2 upregulation has oncogenic potential in certain cancer types, like HCC, [13] leukemia [14] and breast cancer [15].