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Background: The validity of current animal colon cancer models is questionable. This study was performed to evaluate whether colonoscopic injection of a murine colon cancer cell line into the cecal wall of immunocompetent rats leads to a solid tumor. Methods: A bolus of bowel prep was given to BD-IX rats. Anesthesia was injected intraperitoneally. Video fiberscope allowed for irrigation and suction. Failure was inability to reach/inject cecum. Procedure was performed by four surgeons; 100 μl of colon tumor cell suspension (DHD/K12TRb; 10 million cells in 0.1 ml) was injected into cecal wall with 23-gauge needle placed on 3 mm wire resulting in a blister. Rats were allowed to recover. Solid tumor growth was measured at scheduled necropsy at 4 weeks. Sample size (107 rats: type I error 0.05; power 80%) was based on a pilot study. Data were presented as median (range). Results: A total of 107 male BD-IX retired breeders weighing 356 g (range 256-432 g) underwent colonoscopy with submucosal injection of cecal wall. A single solid cecal cancer was identified in 98 (91.5%) rats at scheduled necropsy. Histology confirmed adenocarcinoma with tumor size of 4 mm (range 2.6-8.4 mm). Peritoneal carcinomatosis was found in ten (9.3%) rats. Distant metastases were found in three (2.8%) rats. Complications occurred in four (3.8%) rats: two aspirations and two colon perforations. Conclusions: A solid cecal tumor without carcinomatosis or metastasis has been developed by colonoscopic injection of a rat colon cancer cell line in 79% of immunocompetent rats. [ABSTRACT FROM AUTHOR]