Subtotal colectomy in the dimethylhydrazine-treated rat. A surgical model of colorectal cancer.

The effects of subtotal colectomy on the survival of rats with established colon cancer induced by 1,2-dimethylhydrazine (DMH) have been investigated in an attempt to assess whether it might provide a suitable model of surgical treatment of this disease. 40 female Wistar rats received a regimen of DMH injections (40 mg/kg body weight s.c. every 14 days for 10 weeks) known to produce colon cancer. An additional 10 rats received no DMH, serving as controls (group 1). After presenting with signs of colonic disease at 25 weeks, all DMH-treated rats had diagnostic colonoscopy under general anaesthesia, only those with visible neoplasms (n = 34) being included in the study. These were randomised into two groups: group 2 (n = 13) animals were unoperated controls while group 3 (n = 21) animals had a therapeutic subtotal colectomy with histological confirmation of cancer in the resected colon. The animals were observed until death, the postoperative survival and cause of death at necropsy being compared between groups. The results showed that overall survival (p less than 0.013) and survival from death due to colon cancer (p less than 0.001) were significantly increased in the colectomised group 3 animals compared to unoperated controls (group 2). While 91% of the unoperated controls died of colon cancer, only 8% of the colectomised group died of this cause (p less than 0.001), the remainder dying from unrelated causes, predominantly DMH-induced primary extracolonic cancers. Subtotal colectomy in rats with DMH-induced colon cancer reduces mortality from this disease, providing a suitable model of surgical treatment. However, the high incidence of DMH-induced extracolonic cancers may make the model unsuitable for studies of adjuvant therapy.