PPAT and neoplasm: The relationship between the sensitivity of human tumours in vivo and ATase levels is complex (D'Incalci et al, 1998; Phillips and Gerson, 1999) and has as yet not been fully elucidated, although pre-clinical studies have demonstrated a correlation between tumour ATase levels and sensitivity to nitrosoureas (Margison and O'Connor, 1990; Pegg, 1990).