Long-term molecular changes in WHO grade II astrocytomas following radiotherapy.

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.

Molecular markers relating to malignant progression in Grade II astrocytoma.

OBJECT: Astrocytoma may progress rapidly or remain stable for many years. To clarify whether molecular characteristics could be prognostic factors, several cell cycling-associated molecular alterations in the diffuse astrocytoma have been investigated. METHODS: Thirty-three patients in whom WHO Grade II astrocytoma had been initially diagnosed were assigned to 1 of 3 groups. Group 1 consisted of 10 patients with malignant progression; the tumor had recurred within 5 years and histological analysis had confirmed that the tumor progressed to Grade III or IV. Group 2 consisted of 10 patients in whom there was no malignant progression; the tumor recurred within 5 years, but histological analysis confirmed that the tumor remained at Grade II. Group 3 consisted of 13 patients who did not experience recurrence within 5 years. Expression of Ki 67, TP53, p27, and p21 was examined using immunohistochemical analysis for the tumor samples obtained during the first and second (in recurrent cases) surgeries. Exons 5, 7, and 8 of TP53 were scanned by DNA sequencing. RESULTS: The Ki 67 labeling index expression was significantly higher in Group 1 (even though it was similar between initial and recurrent tumors) than that of Group 3 (p < 0.05). However, there was no difference between Group 2 (both initial and recurrent tumors) and Group 3. The TP53 protein accumulation was also higher in Group 1 than in Group 2 or 3 (p < 0.05); a difference in TP53 expression was not found between Groups 2 and 3. The p27 and p21 was expressed in all cases, but no predictive values were found. The p53 mutation was found only in 6 cases in Group 1. CONCLUSIONS: Overexpression of TP53, TP53 mutation, and Ki 67 labeling index could be molecular markers in astrocytomas predicting malignant progression.