It　is　well　known　that　the　stability　of　RNA,　the　interaction　between　RNA　and　protein,　and　the　correct　translation　of　protein　are　significant　forces　that　drive　the　transition　from　normal　cell　to　malignant　tumor.　Adenosine　deaminase　acting　on　RNA　1　(ADAR1)　is　an　RNA　editing　enzyme　that　catalyzes　the　deamination　of　adenosine　to　inosine　(A-to-I),　which　is　one　dynamic　modification　that　in　a　combinatorial　manner　can　give　rise　to　a　very　diverse　transcriptome.　ADAR1-mediated　RNA　editing　is　essential　for　survival　in　mammals　and　its　dysregulation　results　in　aberrant　editing　of　its　substrates　that　may　affect　the　phenotypic　changes　in　cancer.　This　overediting　phenomenon　occurs　in　many　cancers,　such　as　liver,　lung,　breast,　and　esophageal　cancers,　and　promotes　tumor　progression　in　most　cases.　In　addition　to　its　editing　role,　ADAR1　can　also　play　an　editing-independent　role,　although　current　research　on　this　mechanism　is　relatively　shallowly　explored　in　tumors.　In　this　review,　we　summarize　the　nature　of　ADAR1,　mechanisms　of　ADAR1　editing-dependent　and　editing-independent　and　implications　for　tumorigenesis　and　prognosis,　and　pay　special　attention　to　effects　of　ADAR1　on　cancers　by　regulating　non-coding　RNA　formation　and　function.