Background Genetic events associated to colorectal carcinoma are well chara
cterized, but there is scanty information about this issue in Chilean subje
cts. Aim: To determine the frequency and distribution of exons 5, 6, 7, 8 a
nd 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 car
cinoma. Immunohistochemical expression of p53 was determined in 35 samples.
Results: Thirty one discrete mutations (12 transitions, 11 transversions a
nd 8 insertions) were observed in 21 samples (60%). Nine samples had mutati
ons in exon 5, twelve samples had mutations in exon 6, seven samples had mu
tations in exon 7 and three samples had mutations in exons 8 and 9. Immunoh
istochemical expression of p53 protein was observed in 18 of 35 cases. Ther
e was a high correlation between the genetic alteration and immunohistochem
istry, when p53 was expressed in more the 20% of cells. The positive and ne
gative predictive values of p53 expression were 87 and 80% respectively. Th
ere was a non significant lower mortality among patients with mutations in
their biopsies. Conclusions: These results confirm the involvement of p53 g
ene mutations in colonic carcinogenesis. Immunohistochemical methods for th
e detection of p53 protein have a high predictive value.