KRAS and carcinoma: In one patient (case #4, Table 2) that did not derive from the above mentioned sample pool of 106 mCRC, the KRAS mutation status was discordant between the samples collected before and after cetuximab therapy, but due to further analysis of these samples with clearly different morphological and genomic features (Figure 3) it might be suggested that populations of carcinoma cells heterogeneous with respect to wild-type and mutant KRAS were probably present in the primary carcinoma, but the metastatic clone derived from a KRAS negative population, as reported previously [22, 23].