TP53 and adenoma: APC gene mutations are involved in the initial step of adenoma formation, while Ki-ras mutations make adenomas larger and more severely dysplastic and p53 mutations promote malignant transformation (Bos et al, 1987; Vogelstein et al, 1988; Baker et al, 1989; Fearon et al, 1990; Fearon and Vogelstein, 1990; Miyoshi et al, 1992; Powell et al, 1992).