EXPRESSION OF BCL-2 IN REACTIVE AND NEOPLASTIC ASTROCYTES - LACK OF CORRELATION WITH PRESENCE OR DEGREE OF MALIGNANCY

The bcl-2 protooncogene encodes a 26-kD protein that extends cell surv ival by blocking apoptosis. This protein has been found to be overexpr essed in neoplastic neural cell lines, although its expression in reac tive and neoplastic astrocytes in vivo has not been well characterized . The authors hypothesized that bcl-2 oncoprotein expression in glioma s might be positively correlated with the tumor's degree of malignancy . Sixty-three gliomas of various subtypes and histological grades were immunostained by bcl-2 protein and the percentage of positive cells w as quantitatively assessed. All tumors contained neoplastic cells that were immunoreactive for the bcl-2 protein (range of cell positivity 1 %-53%). It was found that bcl-2 expression did not vary significantly as a function of tumor subtype or grade (p < 0.1, one-way analysis of variance (ANOVA) on ranks) as compared to the cell proliferation marke r Ki-67 (MIB-1) in which a very significant correlation with tumor gra de was noted (p < 0.0000001, one-way ANOVA on ranks). In fact, the hig hest percentage of bcl-2 immunoreactive cells was noted in low-grade g liomas, that is, in juvenile pilocytic astrocytomas and oligoastrocyto mas. The specificity of bcl-2 overexpression was also assessed in 10 n onneoplastic lesions associated with prominent reactive astrocytosis. In nine of these cases (90%), bcl-2-positive reactive astrocytes were observed, often in large numbers, whereas relatively few Ki-67 immunor eactive cells were noted. The authors conclude that bcl-2 oncoprotein expression as assessed immunohistochemically does not correlate with g lial tumor type or grade and its overexpression is not confined only t o neoplastic conditions. Instead, the finding of robust bcl-2 expressi on in low-grade glial tumors and in reactive astrocytes warrants the i nference that resistance to apoptosis is a nonspecific finding in astr ocytes associated with both reactive and neoplastic conditions.