Progress in rare central nervous system tumors.

Abstract

Although all primary central nervous system (CNS) tumors are rare, certain tumor types each represent less than 2% of the total and an annual incidence of about 1000 patients or less. Most of them are disproportionally diagnosed in children and young adults, but older adults can also be affected and are rarely recruited to clinical trials. Recent new molecular techniques have led to reclassification of some of these tumors and discovery of actionable molecular alterations. We review recent progress in the molecular understanding and therapeutic options of selected rare CNS tumors, with a focus on select clinical trials (temozolomide and lapatinib for recurrent ependymoma; vemurafenib for BRAFV600E-mutated tumors), as well as tumor-agnostic approvals (pembrolizumab, larotrectinib) and their implications for rare CNS tumors. Although rare CNS tumors are a very small fraction of the total of cancers, they represent a formidable challenge. There is a need for dedicated clinical trials with strong correlative component in patients of all ages with rare CNS tumors. Critical research questions include relevance of the selected target for specific tumor types, persistence of the actionable biomarker at recurrence, blood-brain barrier penetration, and analysis of mechanisms of primary and acquired resistance.