Characterization of the pseudocapsule of soft-tissue sarcomas. An experimental study in rats.

The effect of preoperative radiation therapy on the pseudocapsule of experimental rat soft-tissue sarcomas has not been histologically evaluated in a controlled study. The irradiated animal showed marked thickening of the capsular structure surrounding the sarcoma. Everywhere morphologically distinct from the tumor, there was no evidence of tumor invasion into or through this capsular structure. The membrane was consistently thicker and more hyalinized than in the control animals. The nonirradiated animals showed a minimal pseudocapsular structure with a characteristic tumor penetration. Irradiation produced distinct histologic changes in the pseudocapsule. Although assumed on the basis of clinical observations alone, irradiation-induced pseudocapsule has not previously been demonstrated in an experimental model of soft-tissue sarcoma.