Clinical application of oligonucleotide probe array for full-length gene sequencing of TP53 in colon cancer.

OBJECTIVE

TP53 mutations are the most frequent genetic alterations in colon cancer. We studied whether the recently developed oligonucleotide microarray technique, GeneChip p53 assay, can be applied to sensitive detection of TP53 gene mutations in surgical specimens from colon cancer patients.

METHODS

TP53 gene mutations in exons 2-11 in 20 colon cancers and the corresponding histopathologically normal mucosa at the surgical margins were assessed by GeneChip p53 assay, and the results were further evaluated by direct sequencing of the involved exon or by mutant-allele-specific amplification (MASA). The expression of TP53 protein was also evaluated immunohistochemically and the result was compared with the gene alteration.

RESULTS

The GeneChip p53 assay detected TP53 mutations in 65% of primary cancers; 61% of the mutations were within the evolutionarily conserved regions, and 46% of the mutations were within the zinc-binding domains (regions of loop 2 and loop 3). Direct sequencing confirmed these mutations. Immunohistochemical examination detected TP53 protein overexpression in 47% of primary cancers, but this protein did not accumulate with all types of TP53 mutations. In addition, the GeneChip assay detected a mutation identical to that in the primary tumor in 2 samples from the surgical margins, and MASA confirmed both mutations, implying the presence of occult cancer cells.

CONCLUSION

The GeneChip p53 assay is sufficiently sensitive to detect TP53 mutations in surgical specimens from colon cancers and may be applicable to screening examination in clinical laboratories as a routine procedure.