Degraded DNA may induce discordance of KRAS status between primary colorectal cancer and corresponding liver metastases

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Abstract
KRAS mutation is widely accepted as a strong, negative predictive marker for anti-epidermal growth factor receptor antibodies, including cetuximab and panitumumab. Previous reports demonstrated approximately 100 % concordance of KRAS status between primary colorectal cancer and liver metastases; however, mismatched KRAS status still occurs. KRAS status was evaluated in 105 pairs of formalin-fixed primary colorectal cancer and corresponding liver metastases specimens by direct sequencing. DNA quality of patients displaying mismatched KRAS status between primary tumors and metastases was assessed using a Bioanalyzer. KRAS status was successfully analyzed in 90/105 patients (85.7 %). The concordance rate between primary tumors and metastases was 88.2 % in synchronous metastases (n = 76) and 100 % in metachronous metastases (n = 14). Discordance in KRAS status was observed in nine patients. Independent method validation revealed only five samples showed the same KRAS status between the two methods. DNA quality assessment by a Bioanalyzer revealed that the median length of DNA samples in the peak concentration of the mismatched group was significantly shorter than those in the control group (153.5 vs 276.5 bp, P = 0.0059). In addition, the median value of the percentage of degraded DNA (0–200 bp) in each sample in the mismatched group was significantly higher than the control group (35.5 vs 22 %, P = 0.020). These data suggest that the discordant results for these nine patients (18 samples) were due to low quality DNA, which may obscure polymerase chain reaction analysis, affecting sequencing reliability. Quality control and assurance of KRAS genotyping is critical, and standardization of the methodology is warranted.

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