The effect of adjuvant immunotherapy on tumor recurrence after segmental resection of carcinogen-induced Wistar/Furth primary bowel adenocarcinomas

Primary bowel tumors were induced in Wistar/Furth (W/Fu) rats by 16 weekly subcutaneous injections of 1,2-Dimethylhydrazine (DMH). After ''curative'' resection of primary adenocarcinomas of the colon, 75% of control rats who received no further treatment developed local or regional recurrence within 22 wk. In 4 separate experiments, rats immunized after primary tumor resection by 3 weekly subcutaneous inoculations of 1 x 106 irradiated (10,000 rad) DMH-W15 sarcoma cells (no tumor-associated antigens cross-reacting with bowel adenocarcinomas) developed recurrent tumor at a rate similar to the controls. By contrast, after primary bowel tumor resection, rats immunized with DMH-W-163 colon adenocarcinoma (possessing tumor-associated antigens cross-reactive with W/Fu bowel adenocarcinomas) showed a consistently reduced rate of local or regional recurrence compared to either of the controls (x2 = 4.62, p < 0.05) or the rats immunized with sarcomas (X2 = 5.42, p < 0.05)= 4.62, p < 0.05). By 22 wk after primary tumor resection, only 35% of the DMH-W-163-immunized animals in each of the 4 experiments showed recurrence. No deaths from recurrences were note in any of the experimental groups after this time, and selected animals sacrificed in the immunized groups up to 30 wk after primary tumor resection were documented to be disease-free. Protection against tumor recurrence was, therefore, a reflection of increased disease-free survival. No change in the effectiveness of immunoprotection in this model could be demonstrated after resection of less invasive primary tumors. These data reflect the utility of a new model in which modification of the natural history of individual primary bowel adenocarcinomas can be examined. The similarities and differences between this system and humans with colon cancer are discussed