Implementation of novel pyrosequencing assays to screen for common mutations of BRAF and KRAS in a cohort of sporadic colorectal cancers.

Activating mutations of the BRAF and KRAS genes cause constitutive stimulation of an important cell-signaling pathway promoting tumorigenesis, and are increasingly recognized as determinants of response to targeted cancer therapies. The V600E mutation accounts for most of the BRAF mutations in cancer, and KRAS mutations are predominantly encoded by nucleotide substitutions within codons 12 and 13. We designed novel pyrosequencing assays for the detection of the common "hotspot" mutations in these genes, which demonstrated analytical sensitivities of <or=10% in titrations of mutant cell lines. The KRAS pyrosequencing assay has the ability to simultaneously identify all potential nucleotide changes within the mutation cluster at codons 12 and 13, with a sequence output in the sense direction to facilitate results interpretation. These assays were used to determine the mutation status in a prospective series of 1198 sporadic colorectal cancers. The BRAF V600E mutation was detected in 13.2% of the colorectal cancers. The frequency of KRAS mutations in our cohort was 32.4%, with G>A transitions at position 2 of codons 12 and 13 being most prevalent. Both assays proved highly sensitive and specific when applied to clinical specimens, and were applicable to both fresh-frozen and formalin-fixed paraffin-embedded archival tissues. These assays would serve as a suitable platform for large-scale mutation detection in cancer specimens where the facility for pyrosequencing is available.