Comparative immunological studies in rats following cryosurgery and surgical excision of 3-methylcholanthrene-induced primary autochthonous tumors.

Post-operative antitumor immunity was studied by comparing the results following cryosurgery and surgical excision of 3-methylcholanthrene-induced primary autochthonous tumors in WKA/Hok rats. Immunity was tested by challenge with the autochthonous tumors on the 4th and 21st days post-operatively. Antitumor resistance which developed following cryosurgery was found in 7 out of 14 rats (50%) challenged after 4 days and in 2 out of 13 rats (15%) challenged after 21 days. Following surgical excision, however, resistance was found in 13 out of 18 rats (72%) challenged after 4 days and in 10 out of 17 rats (58%) challenged after 21 days. Therefore, the development of antitumor immunity by surgical excision was more effective than by cryosurgery (P less than 0.02). In addition, the enhancement of autochthonous tumor growth as compared with that of the control rats was clearly demonstrated after cryosurgery in 4 out of 14 rats (29%) challenged 4 days afterwards and in 3 out of 13 rats (23%) challenged 21 days afterwards. After surgical excision, however, this was seen in only 3 out of 18 rats (17%) challenged 4 days afterwards, and in 0 out of 17 rats (0%) challenged 21 days afterwards. These results suggest not only that the development of antitumor immunity is delayed but also that the tumor growth is more likely to be enhanced by cryosurgery than by surgical excision.