Many types of allelic losses and sequence alterations in chromosomal region 10q23 in several human cancers led to the search for a tumor suppressor gene in this region, receiving various names including PTEN [6], gene mutated in multiple advanced cancers 1 (MMAC1) [15] and transforming growth factor-β-regulated and epithelial-cell enriched phosphatase 1 (TEP1) [7]. Here, PTEN is linked to cancer.