Comparison of KRAS mutation tests in colorectal cancer patients.

The KRAS pathway and studies evaluating KRAS as a prognostic marker in colorectal cancer are discussed along with advances in KRAS gene mutation testing. Highly sensitive real-time polymerase chain reaction (PCR) methods were developed for this purpose. We examined the applicability of direct sequencing and two real-time PCR methods in the diagnosis of KRAS mutations. We used real-time PCR and direct sequencing-based methods to determine applicability of these KRAS mutation tests in 64 colorectal cancers. The two DNA samples found to be mutation positive by real-time PCR were analyzed again after diluting 100-fold. The results were the same. When we applied the same strategy for the direct sequencing, even a 10-fold dilution did not show the mutations. Therefore, we found that sequencing may not be informative when there are only a few mutant cells in the tumor. KRAS mutation screening on formalin-fixed, paraffin-embedded DNA is very efficient with real-time PCR methods in comparison to direct sequencing. The development and adoption of guidelines for KRAS mutation testing are crucial for success.