Morphology and Distribution of 1,2-Dimethylhydrazine Dihydrochloride-Induced Colon Tumors and Their Relationship to Gut-Associated Lymphoid Tissue in the Rat2

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Abstract
The histopathology and relationship of sym-dimethylhydrazine dihydrochloride [(DMH) CAS: 306-37-6; 1,2-dimethylhydrazine dihydrochloride)-induced colon tumors to colonic lymphoid aggregates were examined in outbred male Sprague-Dawley rats treated with saline or DMH and sacrificed at three intervals after treatment. The ratio of polypoid:sessile tumors was 71 :29 four months after DMH treatment and 62:38 when tumors were fully developed. Colonic lymphoid aggregates were found 3-5 cm from the cecal-colonic junction, near the flexure of the ascending and transverse colon, and 3–5 cm from the rectum. There were no significant differences between saline-treated and DMHtreated rats regarding the size, cellularity, and number of lymphoid aggregates per rat. A significant association (P <.001) was seen between tumor development and the presence of a lymphoid aggregate in a given segment of the colon. Sessile adenocarcinomas, but not polypoid tumors, were significantly associated (P <.001) with lymphoid aggregates and usually presented as mucinous tumors adjacent to or intermixed with the lymphoid tissue.