There is evidence, however, to suggest that each of these tumour entities may arise de novo and these studies are based largely on the patterns of mutations in TP53 and K-RAS, each of which can show considerable heterogeneity (Teneriello et al, 1993; Herbst, 1994; Miki et al, 1994; Ortiz et al, 2001). The gene discussed is KRAS; the disease is neoplasm.