NRAS and metastasis: The aim of this study was to describe the intertumoral heterogeneity of mCRC tumors through the mutation frequency of four key driver genes (KRAS, NRAS, PIK3CA and BRAF) in 76 samples from 26 untreated mCRC patients at diagnosis corresponding to 26 primary tumors, 16 lymph node metastases and 34 liver metastasis samples and then to establish the intratumoral pathways of clonal evolution.