Cryo-Forum

From: Proceedings 10th World Congress of Cryosurgery
Cryosurgery of the AT-1 Dunning prostate tumor in vitro, in vivo and in the dorsal skin flap chamber

Cryosurgery, or tissue destruction with freezing, is a promising therapy for the treatment of solid tumors. Two main questions involved in the use of this technique are:

1. What is the mechanism by which freezing destroys tissues, and
2. 2. What part of the cryosurgical iceball is destroyed? An animal model, the AT-1 prostate tumor grown in the Copenhagen rat, has been developed to help answer these questions. Small pieces of excised AT- I tumor were frozen using a directional solidification stage at various freezing rates and end temperatures in order to assess injury in vitro. The tissue was then kept in culture for 1, 3, 5, or 7 days, and then fixed in Bouins solution for later histological examination. Tumors were also grown in the hind limb. They were then frozen using a Cryo-Tech cryoprobe inserted in the tissue, creating an iceball of roughly 11.5 cm completely within the tumor, in order to gain a qualitative understanding of injury in vivo. The tumor was then left in situ and was later excised and fixed at 1, 3, 5, 7, 14, or 21 days after cryoinjury. The in vitro tissue showed signs of nuclear pyknosis and karryorhexis, as well as increased eosinophilia, consistent with cellular level inury. The in vivo tissue showed a neutrophil infiltration at I day post cryo, and macrophages, granulation tissue, and what appears to be fibrosis at 3 to 21 days post cryo. This is typical of the progression from acute inflammation to chronic inflammation and repair as seen after ischemic injury except that the inflammation was limited to a single band surrounding the cryolesion. The tumor was propagated within a dorsal skin flap chamber implanted in the rat, in order to assess vascular injury. Cryosurgery was performed in the chamber with a smaller cryoprobe (-I mm) being placed in the center of the chamber with thermocouples placed within the tumor to monitor the temperature profile. The tumor vasculature was viewed after cryoinjury under brightfield and FITC-labeled dextran contrast enhancement to assess the amount and type of vascular injury. The results showed that there was complete destruction of the vasculature in the center and a gradual return to patency from the center outward. The tissue was removed from the window at I and 7 days post cryoinjury. Histologic examination showed a neutrophil infiltration at the edge of the destroyed region after I day, and macrophages and lymphocytes after 7 days, as was found in the hind limb. Also, the size of the iceball was qualitatively larger than the size of the injury, and roughly corresponded to the area of vascular injury seen. These results are consistent with the hypothesis that vascular injury and inflammation as well as cellular injury are important to the overall tissue destruction.