Novel Universal Classification of Childhood Low-grade Gliomas Using Clinical, Pathological and Molecular Methods

The recent progress in both molecular understanding and the exciting preliminary results of targeted therapies in pediatric low-grade gliomas (PLGG) created both hope for a new era in front of us but also highlighted urgent issues that will be required to be addressed in the near future to optimize and ensure progress in the field.

The international meeting supported by the PLGA foundation in Padua highlighted examples of both the former and the latter.

Perhaps the most significant step forward was achieved by 2 reports on BRAF-V600E PLGG. An international collaboration funded in part by the PLGA Foundation and led by the SickKids and St. Jude groups confirmed that these tumors confer extremely poor outcomes and do not respond to current therapies. In parallel, early data from a prospective trial on these BRAF- V600E tumors using targeted inhibitor led by Dr. Kieran from Boston suggest extremely high response not previously seen in these tumors.

In contrast, specific challenges areas included:

• The need for a universal classification of PLGG for both outcome analysis and clinical trials
• The need to consolidate and synergize future clinical targeted therapeutics supported by pharma
• The need to develop and agree on robust clinical outcome measures for the short and long-term goals.

In order to address the first and most burning issue, a subcommittee of experts from the European Union (EU) and North America started plans to enable such a classification. The major obstacle to such a project is lack of consensus on molecular and pathological tests used among all centers. Specifically, lack of morphological and some mutation analysis in the EU group and lack of methylation arrays as a classification tool in the North American group.

Currently, the largest comprehensive database combining tissue, molecular analysis with long term outcome (>30 years) exist in Ontario, Canada and the St. Jude databases.

With current support of the PLGA Fund, an ambitious project between these centers and other US centers is being carried out to finalize the molecular classification using RNAseq and genome sequencing. However, without parallel methylation array analysis of all tumors, no comparison and classification with the EU will be possible.

To address this issue, we plan to undertake a stepwise approach:

We plan to initially address the first, and most urgent subtype of PLGG, the BRAF-V600E PLGG. We already assembled a cohort of 280 tumors with the mutation. Sequencing and specific copy number analysis were already done on all these PLGG.

Here we plan to finalize this proof of principle testing by performing 850k Methylation arrays on all these tumors. In order to further classify tumors with the EU group, we will also analyze the BRAF PLGG that transformed to high grade gliomas (n=30, Mistry et al, JCO 2015).

After gathering this information, parallel data from the EU tumors will be reanalyzed to see whether molecular classification can add to the current clinical morphological classification of this type of PLGG. This initial step is key as it will serve as a platform for future work including:

• It will inform both current and future clinical trials with BRAF V600E inhibitors.
• It will form the basis of comparative clinical, pathological and molecular analysis for future efforts on other subtypes of PLGG.

Funded in 2017.