The human tumor suppressor, PTEN/MMAC1/TEP1 (PTEN, phosphatase deleted on chromosome ten; MMAC1, mutated in multiple advanced cancers; TEP1, tensin-like phosphatase) is a dual-specificity phosphatase based on the conserved catalytic domain (Li et al., 1997a; Steck et al., 1997). The gene discussed is TEP1; the disease is cancer.