FTO (Fat mass and obesity-associated protein) is an enzyme that acts as an RNA N6-methyladenosine (m6A) demethylase. FTO is the first identified demethylase for internal m6A modification in RNA, which is a dynamic and reversible process. It has the capability to remove the methyl group from m6A and N6,2-O-dimethyladenosine (m6Am) in RNA, primarily found in the 5’-UTR. FTO has been reported to be upregulated in many tumors, and its high expression is associated with shorter overall survival in multiple types of cancer patients. It plays an oncogenic role in acute myeloid leukemia (AML) and is involved in cancer stem cell self-renewal and immune evasion. Targeting FTO suppresses cancer stem cell maintenance and immune evasion, suggesting its critical roles in these processes and highlighting the potential of targeting FTO for cancer therapy. FTO is also implicated in epitranscriptomics, which involves chemical modifications in RNA that affect the fate of modified RNAs.