Azoxymethane (AOM) is a colon carcinogen that is used to study the pathogenesis of sporadic colorectal cancer. We have evaluated differential susceptibility to AOM in inbred mice used as progenitors of recombinant/transgenic lines. In experiment 1, male FVB/N, 129/SvJ, C57Bl/6J mice were treated i.p. with 10 mg/kg AOM once per week for 4 weeks and sacrificed after 20 weeks. Only AOM-treated FVB/N mice developed tumors (3.6 tumors/mouse) in distal colon. In experiment 2, A/J, AKR/J, Balb/CJ mice were treated with AOM for 6 weeks and sacrificed after 24 weeks. AOM-treated A/J and Balb/CJ mice developed 9.2 and 1 tumor/mouse, respectively. Despite these differences, tumors had similar morphology regardless of strain. Immunohistochemistry with β-catenin resulted in marked nuclear and cytoplasmic staining of tumor cells in FVB/N. However, fainter and heterogeneous β-catenin staining was observed in A/J tumors, suggesting distinct pathways of tumorigenesis in different strains. Irrespective of cytological features of malignancy, tumor cells rarely breached the muscularis mucosa and showed no evidence of distant metastasis. Lack of invasiveness and metastasis in even the most sensitive strains provides a model system for studying the potential role of ‘metastasis genes’ in imparting a malignant phenotype.

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