Clinical impact of molecular profiling in rare brain tumors

Purpose of review The purpose of this review is to describe the commonly used molecular diagnostics and illustrate theprognostic importance to the more accurate diagnosis that also may uncover therapeutic targets. Recent findings The most recent WHO Classification of Central Nervous System Tumours (2021) lists over 100 distincttumor types. While traditional histology continues to be an important component, molecular testing isincreasingly being incorporated asrequisitediagnostic criteria. Specific molecular findings such as co-deletion of the short arm of chromosome 1 (1p) and long arm of chromosome 19 (19q) now define IDH-mutant gliomas as oligodendroglioma. In recent years, DNA methylation profiling has emerged as adynamic tool with high diagnostic accuracy. The integration of specific genetic (mutations, fusions) andepigenetic (CpG methylation) alterations has led to diagnostic refinement and the discovery of rare braintumor types with distinct clinical outcomes. Molecular profiling is anticipated to play an increasing role inroutine surgical neuropathology, although costs, access, and logistical concerns remain challenging. Summary This review summarizes the current state of molecular testing in neuro-oncology highlighting commonly usedand developing technologies, while also providing examples of new tumor types/subtypes that haveemerged as a result of improved diagnostic precision.