Expression pattern of apoptotic markers in vestibular schwannomas

The Fas-Fas-L system plays a major role in the regulation of apoptosis and hence in growth in benign and malignant human tumors. As the factors regulating cell death in benign schwannomas are not well understood, we investigated the immunoexpression of the Fas-Fas-L system, as well as that of the anti-apoptotic factor Bcl-2 and the pro-apoptotic factor Bax in 14 sporadic vestibular schwannomas, and related the findings to the MIB-1 labeling index as a marker for cell proliferation. Whereas cytoplasmic Fas expression was seen in only one tumor (7%), Fas-L was found in the nuclei of 12 schwannomas (86%). Bcl-2 expression was found in the cytoplasm of 9 tumors (64%), and Bax was found in 10 out of 14 schwannomas (71%). No significant correlations between different labeling indices were observed. However, schwannomas expressing Bax tended to show a higher proliferation rate as revealed by the MIB-1 LI, suggesting a balance between cell proliferation and cell death. Our study further showed that Fas-L is present in most vestibular schwannomas; however, due to the lack of Fas expression, apoptosis in vestibular schwannomas does not seem to be mediated via the Fas-Fas-L system.