LG-05PEDIATRIC GRADE II GLIOMA MOLECULAR SCREENING IN ADOLESCENTS AND YOUNG ADULTS.

The grade II gliomas are rare and represent 10% of all gliomas in adult and pediatric populations. Those gliomas are mostly represented by a heterogeneous group of oligodendrogliomas, oligoastrocytomas and diffuse astrocytomas. As in rare tumors, the molecular definition is difficult to establish. Furthermore, those tumors are covering a large range of age from adolescent to young adults. Recent advances in young adult grade II gliomas showed a predominance of ATRX loss expression, 1p/19q codeletion and IDH1/2 mutations, whereas in pediatric setting FGFR1, MYBL1 and BRAF were frequently involved. Then, the major question was why the tumors in patients less than 18 years and in young adults were so different molecularly. Therefore, in a cohort of 37 grade II gliomas (7 pediatric patients less than 18 years and 30 adults), a molecular screening based on both pediatric and adult molecular abnomalities was performed. ATRX, 1p/19q codeletion, IDH1/2, FGFR1, MYBL1 and BRAF status was analyzed. This population had a pattern mixing the molecular and histological data previously described but without any age-dependent dichotomy. Some of the pediatric grade II were presenting IDH1 mutation with ATRX loss, whereas few young adults had BRAF mutations. These results suggest that a larger cohort should be closely analyzed to confirm these preliminary data which considered the grade II glioma in a larger group of age than previously.