Mutations of p53 and methylation of p16 in colorectal tumors. (A) Detection of p53 mutations by SSCP and direct sequencing. Aberrantly migrating SSCP bands (reflecting base pair changes) are indicated by arrows (left part of each panel). Shifted bands were excised from gels and were reamplified by using the same set of primers, and direct sequencing was performed by using automated sequencers (right part of each panel). Tumor 703 has a band shift in exon 8 caused by a mutation in codon 282 (CGG to CAG). Tumor 547 has a band shift in exon 7 caused by a mutation in codon 245 (GGC to AGC). Tumor 1290 has a band shift in exon 5 caused by a 10-bp duplication that creates a premature stop codon. N, normal tissue; T, colorectal cancer. (B) Frequencies of alterations of p53 and p16 in CRCs. Forty-one CRCs are divided into four categories based on the presence of alterations of p53 (p53+) and/or p16 (p16+). Alterations of p16 and p53 were inversely correlated (P = 0.0007, Fisher's Exact test). (C) Summary of alterations of p53 and p16 in colorectal tumors with or without CIMP. The frequencies of alterations in p53 and p16 in cancers and adenomas are expressed as percentages. n, number of tumors analyzed.