Alterations in tumor microvasculature during hyperthermia.

The pattern of response of tumor microvasculature to heating at 41 degrees C, 43 degrees C, and 45 degrees C for 30 minutes was studied in squamous cell carcinoma grown in the cheek pouch chamber of the hamster. At each temperature, the immediate response was a prominent reduction in vascular caliber. This was followed by a return to preheating caliber at 41 degrees C, vasodilatation at 43 degrees C, and vasodilatation in some tumors at 45 degrees C. Minimal pathologic alterations occurred in the vascular stroma at 41 degrees C, while at 43 degrees C, petechiae, stasis, occasional thromboses, some endothelial degeneration, and persistent hyperemia were characteristic. At 45 degrees C, compression/occlusion, hemorrhage, and stasis/thrombosis occurred, and in each tumor, complete shutdown of circulation led to a picture typical of coagulation necrosis. Pathophysiologic changes in the microvasculature of a tumor subjected to hyperthermia may account for a greater degree of cure than can be attributed to direct cell killing.