A comprehensive procedural approach to genotyping KRAS and BRAF from paraffin embedded tissues for diagnostic purposes.

Background: Mutations in the Kirsten Ras 1 (KRAS) and V-Raf Murine Sarcoma Viral Oncogene Homolog B1 (BRAF) genes may be predictive of response to drugs directly linked to the Epidermal Growth Factor Receptor (EGFR) signaling pathway.
Materials and Methods: A total of 230 samples from patients with metastatic colorectal cancer were analyzed for KRAS exon 1 and 2 and for BRAF exon 15 mutations. DNA from paraffin-embedded tumor sections was analyzed using microdissection, direct sequencing analysis and allelic separation by cloning.
Results: KRAS mutations were present in 44.3% of the tumor samples. The mutation frequency at hot-spot codons of exon 1 was 84.2%, whereas non-canonical variants had a frequency of 11.8%. Approximately 4% of the cases exhibited concomitant variations. BRAF mutations were present in 3.9% of the tumor samples.
Conclusion: Our experience suggests that sequential microdissection, direct sequencing and allelic separation by cloning may improve the approach to mutational analysis of KRAS and BRAF in patients with colorectal cancer.