Abstract: The DNA copynumber variant  (CNV) is a kind of segments of DNA ranging from 1 kb to 3 Mb that is present in a variable number of copies. CNVs widely distribute across the human genome, and dramatically increases genetic diversity. In recent years，researches have found that most CNVs are closely related to complex diseases. If a cancer gene is directly encompassed or overlapped by a CNV, it may lead to activation of oncogenes or inactivation of tumor suppressor genes, and finally results in tumorigenesis. CNVs can affect gene expression, phenotype differences and phenotypic adaptations by changing gene dosages and gene activities，and then sequentially lead to tumor or any other genetic dieases. Investigating CNVs is apparently helpful for studing chromosome recombination, genomic evolution, gene expression and the pathogenesis of multiple complex diseases especially tumor.

Key words: Neoplasms, Variation (genetics), Genetic predisposition to disease