Monitoring the long-term radiotherapy-associated molecular changes in low-grade gliomas(LGGs) facilitates the understanding of LGG response to radiotherapy.In this study,we used immunohistochemistry to analyze the expression of Ki-67,tumor protein P53(TP53),P21,and P27 in 8 paired WHO grade II astrocytoma samples.The interval between radiotherapy(RT) and the second surgery was more than 3 months in all cases.The average Ki-67 labeling index(LI) was 5.3% in pre-RT samples and 11.54% in post-RT samples.Ki-67 LI was higher in the primary tumors that underwent malignant transformation observed at the second surgery after radiation.Post-RT Ki-67 LI decreased in 2 cases with an interval of less than 12 months between RT and the second surgery.TP53 expression was found in 3 out of 4 pre-RT samples with malignant transformation and in 1 out of 4 pre-RT samples without malignant transformation.Post-RT TP53 increased in 2 cases in which increased expression of P21 or P27 was also observed.Our study suggests that radiotherapy can inhibit WHO grade II astrocytoma proliferation as reflected by Ki-67 LI,but the effect attenuates with time.In addition,there is a tendency of malignant transformation for WHO grade II astrocytomas with a high Ki-67 level or TP53 expression in initial samples. Monitoring the long-term radiotherapy-associated molecular changes in low-grade gliomas (LGGs) facilitates the understanding of LGG response to radiotherapy. In this study, we used immunohistochemistry to analyze the expression of Ki-67, tumor protein P53 P21, and P27 in 8 paired WHO grade II astrocytoma samples. Interval between radiotherapy (RT) and the second surgery was more than 3 months in all cases. Average Ki-67 labeling index (LI) was 5.3% in pre-RT samples and 11.54% in post-RT samples. Ki-67 LI was higher in the primary tumors that underwent malignantant transformation observed at the second surgery after radiation. Post-RT Ki-67 LI decreased in 2 cases with an interval of less than 12 months between RT and the second surgery. TP53 expression was found in 3 out of 4 pre-RT samples with malignant transformation and in 1 out of 4 pre-RT samples without malignant transformation. Post-RT TP53 increased in 2 cases in which increased expression of P21 or P27 was also observed.Our st udy suggests that radiotherapy can inhibit WHO grade II astrocytoma proliferation as reflected by Ki-67 LI, but the effect attenuates with time. addition, there is a tendency of malignant transformation for WHO grade II astrocytomas with a high Ki-67 level or TP53 expression in initial samples.