Background and purpose: Metastatic colorectal cancer (mCRC) patients with K-ras mutation won’t benefit in the anti-epidermal growth factor receptor (EGFR) treatments. Thus K-ras mutation analysis is mandatory before this treatment. There is controversy that K-ras mutation analysis should be performed on primaries or related metastases. The aim of our study was to evaluate the concordance of K-ras status between primary and related metastases tumors

thus investigate the validity and rigorousness of clinical K-ras testing. Methods: Seventy-six patients with confirmed mCRC treated in Fudan University Shanghai Cancer Center were enrolled. After DNA extraction and PCR amplification

tumor specimens with paired primary tumors and related metastatic sites were put into sequencing analysis. And the K-ras mutation status in exon 2 was assessed. Results: K-ras mutation was detected in 31 out of 76 primary tumours (40.8%) and also 40.8% of the metastatic sites. But discordance was found between primary tumor and metastasis in 15 cases (19.7%): 8 primary tumors had a K-ras mutation with a wildtype metastasis

meanwhile 7 primary tumors were wild type with a K-ras-mutated metastasis. Conclusion: Our study indicated that quite a few mCRC cases have different K-ras status between primary tumors and related metastatic sites

and it’s not very rigorous to choose the anti-EGFR treatments merely according to the primary tumor-K-ras mutation. Further study and consultation are needed on this problem.