Enhancement of experimental pulmonary metastasis and inhibition of subcutaneously transplanted tumor growth following cryosurgery.

We have previously reported that inhibition of anti-tumor immune responses and a correspoding enhancement of metastatic tumor growth occurred in rats following cryosurgery of 3-methylcholanthrene-induced WKA rat fibrosarcoma (KMT-17). In this study, to evaluate the enhancement of metastasis arising from the inhibition of anti-tumor immune responses following cryosurgery, we examined how cryosurgery affected experimental pulmonary metastasis and the growth of subcutaneously transplanted tumor. To reveal the effect of cryosurgery on pulmonary metastasis, rats received a subcutaneous inoculation of KMT-17 tumor in the right flank (1×10 6 ) and i.v. injection (1×10 5 , on the same day or 4 days later. The right flank tumors were treated with cryosurgery 5 days after subcutaneous transplantation. The pulmonary metastasis of the rats, which were injected i.v. one day before treatment, was enhanced by cryosurgery as compared with surgical excision, though the pulmonary metastasis of rats, which were injected i.v. 5 days before treatment, was un-affected by cryosurgery. These observations suggest that cryosurgery may enhance the pulmonary metastasis in its early steps but has no effects in its later stages. To reveal the effect of cryosurgery on the growth of distant tumors, rats received subcutaneous inoculations of KMT-17 tumor in the right (1×10 6 ) and left (1×10 4 ∼ 10 5 ) flanks. Tumors in the right flank were treated with cryosurgery 5 days after inoculation and the growth of untreated left flank tumors was observed. In this double grafted tumor system, however cryosurgery significantly inhibited the growth of the unttreated left flank tumors. Spleen cells obtained from rats which had undergone cryosurgery 4 or 10 days previously (cryo-spleen cells) were used for in vivo neutralizing Winn assay. Antitumor activity of cryo-spleen cells was decreased as compared with that of rats after surgical excision in both spleen cells from 4 and 10 days after treatment. These findings suggest that effector cells in the spleen may not participate in subcutaneous tumor regression and that the evaluation of antitumor effect using the double grafted tumor system needs caution.