The tumour suppressor gene PTEN, located on chromosome 10q23, encodes a protein tyrosine phosphatase and is frequently deleted and mutated in various malignancies, including glioblastomas, breast and prostate cancer (Steck et al, 1997; Li et al, 1997b; Sano et al, 1999; Perren et al, 2000). The gene discussed is PTEN; the disease is glioblastoma.