Compared with tumors harboring class 1 mutations, colorectal cancers with atypical BRAF mutations in classes 2 and 3 tended to occur in the distal large bowel (Table 1; Fig. 3A), with 58% of tumors occuring in the distal colon versus 16.3% in the proximal colorectum (P < 0.001, Fisher exact test), consistent with previous reports (5, 7, 35). This evidence concerns the gene BRAF and colorectal cancer.