To the Editor.—Prayson and Suh1 recently reported the results of MIB-1 immunohistochemical analysis in a study of subependymomas and other ependymal neoplasms. We also recently published immunohistochemical data (MIB-1, p53, and bcl-2) in a series of 37 ependymal neoplasms, including 10 subependymomas.2 Our findings were similar to those of Prayson and Suh with very low to negligible MIB-1 reactivity in the grade I ependymomas, mean labeling indices of 1.7% and 1.3% in grade II ependymomas (not otherwise specified) and papillary ependymomas (also grade II), respectively, and a mean labeling index of 34% in our anaplastic ependymoma group. In our series, the subependymomas that gave rise to clinical symptoms had slightly higher MIB-1 labeling indices than those found incidentally at autopsy, suggesting that even marginal differences in growth rate might affect the clinical presentation.
In a separate study,3 we also demonstrated a virtual absence of telomerase activity in all our subependymomas, which is certainly in keeping with the authors' suggestion that these lesions may “be more akin to hamartomatous lesions than to true neoplasms.”