Alterations in p53, p21, and MIB-1 labeling index in primary human astrocytomas following radiation therapy

Little is known about the cellular and genetic changes that occur in human astrocytomas following radiation therapy (RT). Experimental studies would suggest that early effects include induction of p53 and p21 expression, cell cycle arrest, and selection of tumor cells with molecular changes that correlate with radiation resistance. Unfortunately, tissue sampling of primary human astrocytomas closely following radiation therapy is uncommon, hindering comparative assessment of primary human tumors. Through local databases, we were able to collect eight cases in which tissue was resected within 8 weeks of RT because of bulky residual disease: two patients with grade II diffuse astrocytomas (LGA) and 6 patients with high-grade astrocytomas (HGA; 1 anaplastic astrocytoma, 5 glioblastomas). Routine histopathologic sections, MIB-1 labeling index (LI), p53 and p21 expression, and EGFR expression were compared between the pre- and post-RT samples. Only one tumor (52d post-RT) showed prominent radiation-induced histopathologic changes. p53 expression was detected in two tumors pre-RT and in six tumors post-RT. In the four tumors in which p53 expression was induced, the post-RT LI was lower in each case, and p21 expression had increased in 3/4 of these cases. No change in LI was detected in tumors in which p53 expression was unchanged. EGFR expression was not altered following RT. The results of this unique series document that some primary human astrocytomas increase expression of p53 and p21 and decrease proliferation in response to RT. However, the small size of the series argues for further studies of radiation induced molecular changes in primary human astrocytoma tissue.