ZEB1 and neoplasm: Surprisingly, compared with Braf-mutant mice with basal levels of Zeb1, the downregulation of Zeb1 downregulation in that model (BVZ+/–) increased the total number and the size of large intestinal lesions or tumors, suggesting that ZEB1, besides having a role in tumor initiation, also contributes to tumor growth (Figure 1, B and C).