(A) Apc^1638N/+; Villin^CreERT2; p120^fl/fl mice were treated with corn oil alone or with TAM dissolved in corn oil (n = 6 per group). At 8 months after injection, mice were sacrificed and total number of tumors throughout the small and large intestine was determined using a dissecting microscope. Tumor multiplicity was increased 10-fold in TAM-treated mice (49 ± 6 vs. 4.5 ± 1, ***P < 0.001, unpaired t test with Welch’s correction). Error bars represent SEM. (B) Tumor number was increased in TAM-treated mice in all 3 regions of the small intestine, cecum, and colon. Error bars represent SEM. PSI, proximal; MSI, middle; DSI, distal. (C) Representative small intestinal tumors from oil- and TAM-treated mice stained for p120 and β-catenin. p120 Immunoreactivity was reduced and cytosolic β-catenin enhanced in tumors (dotted lines) from both oil- (top panel) and TAM-treated (middle and bottom panels) mice as compared with adjacent normal tissue (arrowhead). Despite its genetic ablation, complete (biallelic) p120 KO was never observed in tumor tissue (e.g., area encircled by dotted line, bottom panel, n = 52 tumors), but occurred frequently in adjacent WT tissue (encircled by solid line). Scale bars: 100 μm. (D) Tumor (T) and adjacent normal (N) tissue were isolated by LCM. DNA was isolated and amplified by PCR and then separated by electrophoresis to confirm retention of 1 allele in tumor tissue. (E) Apc^Min/+; Villin^CreERT2; p120^fl/fl mice were injected with TAM and sacrificed 3 months later. Pockets of p120-null cells (solid line) were frequently observed embedded in and around adenomatous tissue (dotted lines), yet these areas invariably proved to be WT upon closer inspection (as evidenced by absence of β-catenin and WT H&E staining, n = 191 tumors). Adjacent normal staining marked by arrowhead. Scale bars: 100 μm.