Concordance of KRAS mutation status between luminal and peripheral regions of primary colorectal cancer. A laser-capture microdissection-based study

The presence of KRAS mutation in colorectal cancer (CRC) is a marker of resistance to anti-EGFR therapy. However, there are conflicting reports concerning intratumoral heterogeneity of KRAS mutations. The aim of this study was to determine whether within primary CRCs with KRAS mutations intratumoral KRAS mutation heterogeneity can be detected between two strictly defined areas, i.e. the luminal (mucosa/submucosa) and peripheral invasive front of the tumor. Using laser-capture microdissection, from every tumor about 400-500 nests of cancer cells were excised from each of the examined areas (luminal and peripheral) and PNAClamp, a high-sensitivity real-time PCR-based diagnostic assay for KRAS mutation testing, was used for molecular analysis. KRAS mutations were detected in codon 12 in both luminal and peripheral regions in all tumors examined. We conclude that from the point of view of practical KRAS mutation testing for predictive purposes in patients with CRC (i.e. testing mutations in codons 12 and 13) sampling errors are unlikely to occur if in CRCs with KRAS mutations only the luminal (as in biopsy tissue) or peripheral region is examined, provided a sensitive system of detection is applied and an appropriate number of tumor cells with minimal contamination by benign cells is analyzed.