Phylogenetic Analysis of Intra-tumor Molecular Heterogeneity on a Pilot Series of Diffuse Low-grade Multilobar Gliomas: Tumor Ontogenesis and Therapeutic Implications

Low-grade diffuse glioma (GDBG) are rare tumors of young adults, whose ontogenesis is poorly understood. Patient management is based on the molecular profile defined by two molecular markers : mutations of the IDH genes and chromosomal 1p19q co-deletion. To date, the IDH and 1p19q statuses are determined on a single fragment collected from the tumor. In the case of GDBGs infiltrating several brain lobes, the sampling is done randomly on only one of the infiltrated lobes. An intra-tumoral heterogeneity of genetic alterations has been suggested and would impact management.

Phylogenetic analysis of genetic alterations found, by high throughput sequencing, in each lobe invaded by the same GDBG will make it possible to assess intra-tumoral heterogeneity and to discuss, at a fundamental level, the hypothesis of a single tumor site with secondary diffusion or that of the convergent progression of two or three distinct tumor sites. Clinically, understanding the ontogenesis of GDBGs will improve their management because of the known link between brain location, dominant molecular profile, and prognosis.