p53 gene mutation in colorectal carcinoma

Background Genetic events associated to colorectal carcinoma are well characterized, but there is scanty information about this issue in Chilean subjects. Aim: To determine the frequency and distribution of exons 5, 6, 7, 8 and 9 mutations and the immunohistochemical expression of p53 gene in biopsy samples of colorectal carcinoma. Material and methods: p53 gene exons 5, 6, 7, 8 and 9 were directly sequenced in 42 biopsy samples of colorectal carcinoma. Immunohistochemical expression of p53 was determined in 35 samples. Results: Thirty one discrete mutations (12 transitions, 11 transversions and 8 insertions) were observed in 21 samples (60%). Nine samples had mutations in exon 5, twelve samples had mutations in exon 6, seven samples had mutations in exon 7 and three samples had mutations in exons 8 and 9. Immunohistochemical expression of p53 protein was observed in 18 of 35 cases. There was a high correlation between the genetic alteration and immunohistochemistry, when p53 was expressed in more the 20% of cells. The positive and negative predictive values of p53 expression were 87 and 80% respectively. There was a non significant lower mortality among patients with mutations in their biopsies. Conclusions: These results confirm the involvement of p53 gene mutations in colonic carcinogenesis. Immunohistochemical methods for the detection of p53 protein have a high predictive value.