Although further studies are necessary to characterize the mechanism underlying NNMT expression in OSCC cell lines and clarify the role of the enzyme in cancer cell metabolism, the present study demonstrates that NNMT downregulation reduces cell proliferation as well as tumorigenic capacity of OSCC cells in vivo, suggesting that NNMT has not only an impact on cell growth, as previously demostrated, but also on cell tumorigenicity. This evidence concerns the gene NNMT and cancer.