Preliminary Studies on Factors Controlling the Rate of Regrowth of Heavily X-Irradiated Rat Rhabdomyosarcoma Tumors.

摘要

Following large single doses of x rays,rat rhabdomyosarcoma tumors exhibit a volume response which characteristically has a swelling phase, a regression phase, a rapid ''initial''regrowth phase and a slow ''late''regrowth phase. The preliminary experiments reported here were designed to examine three mechanisms that may underlie the reduction in growth rate occurring in the late regrowth phase; heritable non-lethal cellular damage,host immunity,delayed post-irradiation tissue and vascular damage. Based on retransplantation experiments and studies with immunosuppressed rats,neither heritable non-lethal damage nor host immune factors appear to influence the regrowth rate of tumors receiving radiation doses well below the cure level. After an x-ray dose approaching the cure level, regrowing tumors were observed to have a greatly reduced growth rate,possibly reflecting the presence of heritable non-lethal damage and/or an increased antigenicity of the heavily irradiated tumor cells. Morphometric analysis of histological sections did not reveal statistically significant abnormalities at the cellular level during the late regrowth phase,except for an increase in the percentage of necrotic tissue relative to non-irradiated tumors. The morphological resolution of small blood vessels was not adequate to evaluate delayed vascular damage in regrowing irradiated tumors. (ERA citation 03:041658)