Based on this understanding of AID’s function, it is proposed that AID is involved in tumorigenesis through three mechanisms: (i) inducing promoter mutations and chromosome translocations of tumor-associated genes through AID’s mutagenic activity; (ii) mediating epigenetic modifications of tumor-associated genes through AID’s demethylation activity; and (iii) regulating the transcription of tumor-associated genes through AID’s function as a transcription cofactor. This evidence concerns the gene AICDA and neoplasm.