What gene mutations do you always test for prior to starting EGFR inhibitor therapy in metastatic colon cancer?  

At a minimum, I operate with pan-RAS, BRAF (yes, even for left sided tumors), MMR/MSI, RNA fusion/rearrangement, and HER2 testing prior to anti-EGFR therapy. Obviously, you would not want to give an EGFR inhibitor to a RAS mutated cancer, but similarly, I need to know the BRAF (particularly V600E) u...