Microdissection-based genotyping assists discrimination of reactive gliosis from glioma

We used molecular anatomic pathology to determine the mutational status (loss of heterozygosity [LOH]) to make the distinction between reactive gliosis and glial neoplasia. LOH has been shown to be absent in reactive states and present in neoplastic cellular proliferations. Three groups of patient specimens were analyzed: group 1, reactive gliosis (n = 15); group 2, gliomas of varying histologic type and grade (n = 54); group 3, diagnostically challenging reactive gliosis vs glioma (n = 16). No group 1 cases (0/15 [0%]) showed allelic loss, whereas all high-grade glial neoplasms, a subset of group 2 (35/35 [100%]) manifested at least 1 allelic loss alteration, with most cases (33/35 [94%]) displaying 2 or more such changes. During a look forward at the group 3 patients, clinical history clarified the problematic diagnosis in a subset of 11 patients: 8 (73%) of 11 clinical outcomes were predicted correctly by our analysis. The molecular anatomic pathology approach outlined herein is designed for minute, formalin-fixed, paraffin-embedded specimens, which are encountered in everyday surgical pathology practice. Molecular anatomic pathology opens the possibilities of molecular analysis to everyday pathology practice.