PTEN and neoplasm: Several studies using either primary tumour tissue or established tumour cell lines have demonstrated a high frequency of PTEN mutation/deletion in various human cancers including brain, bladder, breast, prostate and endometrial cancers (Louis and Gusella, 1995; Cairns et al, 1997; Li et al, 1997; Risinger et al, 1997; Tashiro et al, 1997; Teng et al, 1997; Podsypanina et al, 1999; Mutter et al, 2000).