KRAS and colorectal carcinoma: Prior work by El-Deiry and colleagues demonstrated clear molecular differences among different metastatic sites of CRC and primary tumors, including higher Her2/neu expression in lung metastases than primary tumors (4% vs. 1.8%, P = 0.028), higher rates of KRAS mutations in brain and lung metastases than other sites (65% vs. 59% vs. 47%, P = 0.07 and < 0.01, respectively), and higher TOPO1 expression in metastatic tumors than primary tumors (52% vs. 30%) [16].