Ultrastructural effects of therapeutic irradiation on human epithelial tumors

Irradiation induces several cellular changes leading to death of cancer cells and normal cells which is followed by repairing processes of normal cells. We have studied the effects of therapeutic irradiation on head and neck cancers. Tissue samples taken before and during the radical irradiation (50-80 Gy) of the squamous cell carcinomas of the head and neck region were examined by light and electron microscopy. Nuclear atypia was most pronounced cellular change during irradiation. The tumor invasion pattern remained unchanged but the number of mitoses decreased. Lymphocytic infiltration increased at the beginning of the therapy (from 10 to 30 Gy) but decreased at the end of radiotherapy. The amount of neutrophils and the keratinization pattern remained almost unchanged at the light microscopical level. However, by electron microscopy, intracellular filaments and desmosomes tended increase slightly especially in tumors responding more favorable to the treatment. The changes in nuclear morphology pointing in a more undifferentiated direction are considered to be due to cell damage rather than to a more aggressive behavior of the tumor cells. This is in agreement with the simultaneous decrease in mitoses, which might partly be due to radiation induced arrest of tumor cells to the G2 phase. These observed changes correspond to animal studies in the literature and might be responsible for the disappearance of tumors during irradiation.