Stereomicroscopic features of colitis-associated tumors in mice: Evaluation of pit pattern

Patients with longstanding ulcerative colitis have an increased risk of colorectal cancer. Mouse models for colitis-associated tumors are indispensable for the development of novel strategies for prevention and intervention, as well as an improved understanding of the mechanisms underlying tumor formation. The present study examined whether stereomicroscopic observations with dye-application were able to detect and discriminate tumors in a colitis-associated tumor model in mice. Colonic tumors were induced in C57BL/6 mice by 15 cycles of treatment with dextran sulfate sodium (DSS) in drinking water. The mice were then divided into 4 groups: normal mice fed a control diet, normal mice fed an iron-supplemented diet, 0.7% DSS mice fed an iron diet and 1.5% DSS mice fed an iron diet. The entire colons were characterized with respect to both morphology and histology. The pit pattern architecture was analyzed using stereomicroscopy with dye agents (0.2% indigo carmine or 0.06% crystal violet). The tumor histology was graded as negative, indefinite or positive for dysplasia. The positive category was divided into two subcategories: low-grade dysplasia (LGD) and high-grade dysplasia (HGD). The tumor incidences and multiplicity were significantly higher in mice fed an iron diet and 1.5% DSS compared with in mice fed an iron diet and 0.7% DSS. Compared with LGD, HGD was predominantly located in the distal colon, was larger in size and had a higher incidence of elevated lesions (Is and IIa) and a lower incidence of flat lesions (IIb). In regards to the pit pattern, HGD had a high incidence of V_I pits and a low incidence of IV, III_L and II pits. In conclusion, evaluation of the pit pattern using stereomicroscopy with dye-application is useful for detecting and discriminating neoplastic changes in DSS mice and may further our understanding of the mechanisms that induce tumor formation in patients with ulcerative colitis and the characterization of pharmaceutical responses.