Animal procedures were performed in accordance with guidelines from the local animal ethics committee. Two cohorts with 15 C57BL/6J-APCmin/+ mice (Jackson Laboratory, Maine) each were fed control chow or PLX4720 (the laboratory tool compound for vemurafenib)-infused (high dose) chow (13 (link)) for 28 days. Upon sacrifice, small intestine and colon were cut open length-wise, and polyp number and size were evaluated in a blinded fashion for proximal small intestine (PSI), distal small intestine (DSI), and colon using a Nikon SMZ645 microscope. Wild type C57Bl6 mice were treated with control and PLX chow for 6 months and sacrificed. All gastrointestinal tracts were formalin fixed, and paraffin embedded. Immunohistochemistry for phospho-ERK, and beta-catenin, was performed as previously described (14 (link)) using the following antibodies: phospho-ERK (Cell Signaling 4370); beta-catenin (Cell Signaling 9562). Stained slides were evaluated for histological features of mouse intestinal polyps, the number of polyps, and nuclear phospho-ERK and β-catenin were scored in a blinded fashion. For the latter, a polyp with a well oriented section, permitting evaluation of luminal and basal epithelium and with the highest proportion of nuclear staining was given an estimated percentage of positive nuclei in the polyp.