Stereotactic biopsies are increasingly being used for the diagnosis and grading of astrocytomas, and there is a growing need to obtain maximum information from these tissue samples. In everyday practice, p53 protein and Ki-67 immunohistochemical analyses are the most frequently used ancillary studies to aid in diagnosis and grading, but their exact role is not clearly established. This study was undertaken to evaluate the practical value of these markers in stereotactic biopsy samples from diffuse astrocytomas as well as pilocytic astrocytomas. Methods/Results.-We analyzed the Ki-67 (MIB-1) and p53 labeling indexes in the stereotactic biopsy specimens from 11 pilocytic astrocytomas; 8 grade 2, 15 grade 3, and 16 grade 4 diffuse astrocytomas. Pilocytic astrocytomas and diffuse astrocytomas were evaluated as 2 separate groups. There was a strong correlation with poor outcome when both labeling indexes were higher than 15% in the same tumor for diffuse astrocytomas (P < 0.01). The indexes did not correlate with outcome in pilocytic astrocytomas.
Combined Ki-67 and p53 labeling indexes higher than 15% indicated a worse outcome than suggested by the histologic grading. The analysis aided or improved histologic evaluation of stereotactic biopsies in our patients. We believe that a realistic prognostic upgrading of diffuse astrocytomas should be made only when labeling indexes for both markers are greater than 15%.