Radiation change versus recurrent astrocytoma: diagnostic utility of the proliferation index?

Differentiation of recurrent glioma from radiation damage can be a challenge to neurologists, neurosurgeons, neuroradiologists, and even neuropathologists. We hypothesized that by evaluating sections of recurrent lesions with proliferation markers we might objectively differentiate between radiation damage gliosis and recurrent astrocytoma. We compared the labeling indices of radiation damage and recurrent neoplasm immunohistochemically, using an antibody to MIB-1, a monoclonal antibody to the Ki-67 proliferation marker. Five of the six recurrent neoplasms were gliomas; four these were astrocytic tumors. In most cases, the MIB-1 LI of radiation damage was < 1% and the LI of recurrent neoplasm was > 3%, with pertinent exceptions. We discuss our findings and their possible interpretation.