PTEN and neoplasm: Overexpression of the TSG PTEN has been shown to reduce the amount of tumor growth in a mouse mammary cancer model of Wnt-1 overexpression.101 Similarly, overexpression of the TSG RB1 inhibits tumor progression in metastatic melanoma cells.102 Since many proto-oncogenes are involved in promoting cell cycle entry, they would therefore potentially decrease proliferation when decreased in expression.