In these tumors, TET1 is mostly considered to be a tumor suppressor, while it is also reported as an oncogene [16]; it binds directly to the promoters of anti-oncogenes, catalyzes 5-mC hydroxylation to initiate demethylation, and induces target genes involved in transcriptional activation, such as phosphatase and tensin homolog (PTEN) in gastric cancer [6]. The gene discussed is PTEN; the disease is gastric cancer.