Choosing First-Line Therapy in PLGG: Chemotherapy, Targeted Agents, and Tumor Biology

In this segment, Dr. Chintagumpala, Dr. Chi, Dr. Margol, and Dr. Abdelbaki discuss first-line treatment selection for pediatric low-grade glioma (PLGG) harboring BRAF fusions or BRAF V600E mutations, and the unanswered question of tumor senescence.

The current regulatory landscape includes FDA approval of dabrafenib plus trametinib for newly diagnosed BRAF V600E-mutant PLGG and tovorafenib for BRAF-altered tumors in the recurrent setting. No targeted therapy is approved as first-line for BRAF-fusion PLGG, and head-to-head comparisons with chemotherapy are still underway.

The panel agrees that carboplatin and vincristine remains the evidence-based standard for newly diagnosed BRAF-fusion PLGG but acknowledges that extenuating circumstances—distance from the treatment center, family burden, inability to place a port, or a child's anxiety about intravenous therapy—can make a first-line MEK inhibitor such as selumetinib a reasonable alternative. Dr. Abdelbaki shares a case of a 14-year-old with a spinal cord pilocytic astrocytoma whose family refused port placement, leading to first-line selumetinib. The panel emphasizes that when targeted agents are used upfront, families must understand that chemotherapy remains the standard, that long-term outcomes with targeted agents are not yet established, and that chemotherapy may still be needed subsequently.

The discussion also highlights that chemotherapy continues to produce excellent responses, including vinblastine, and that stable disease is itself a meaningful outcome. The panel raises the critical question of tumor senescence: PLGG tumors are expected to "burn out" at some age, but it is unknown whether targeted inhibitors alter this biologic clock, potentially prolonging the overall treatment course compared to conventional chemotherapy.

For BRAF V600E-mutant tumors, the panel notes that dabrafenib plus trametinib has demonstrated superiority over both chemotherapy and single-agent trametinib but has not been compared to single-agent dabrafenib. Some panelists favor starting with single-agent dabrafenib for typical-appearing low-grade gliomas, citing favorable outcomes with single-agent BRAF inhibitors including vemurafenib on the PNOC study, and reserving the combination for tumors with additional concerning molecular alterations or more aggressive histology such as pleomorphic xanthoastrocytoma (PXA).

In the next episode, "Clinical Trial Endpoints in PLGG: Rebound Regrowth, and the Unanswered Question of Tumor Senescence," the panel debates which endpoints best capture treatment benefit and confronts persistent gaps in long-term survivorship data.