ETMR-07. DNA methylation profiling of a series of rare CNS embryonal tumors in children: diagnostic and clinical impact

BACKGROUND: CNS embryonal tumors are a clinically and biologically heterogeneous group of tumors, more frequently arising in very young children. In the last few years, tumor classification through DNA methylation profiling has been demonstrated to be a powerful diagnostic tool which could be especially informative in this setting. METHODS: We reviewed original diagnosis and molecular profile of childhood CNS embryonal tumors other than medulloblastoma or AT/RT from a retrospective single-center cohort. Sixteen FFPE tissue samples from 14 unique patients (diagnosed from 1996 to 2017) were analyzed using DNA methylation arrays and matched with the Heidelberg classifier. Then, cohort characteristics and outcome were re-evaluated according to the results of the array. RESULTS: Median age at diagnosis was 2.7 years; there was no statistically significant difference between ETMRs and CNS embryonal tumors, NOS. Male to female ratio was 4:3. Median OS was 17,5 months (IQR 10.2-103.3 months) and ETMRs presented the worst outcome. Methylation profiling matched with an adequate score in 50% of samples (8/16). DNA methylation profile was consistent with ETMR in two samples but only one showed amplification of C19MC. Seven CNS embryonal tumors, NOS were properly reclassified as supratentorial ependymoma and diffuse pediatric-type HGG (4 and 1) or better defined as CNS neuroblastoma, FOXR2-altered (2). Methylation profiling added a unique diagnostic contribution in 64.3% of all cases (9/14). After the integration of methylation array results, survival markedly differed according to the novel integrated diagnoses; supratentorial ependymomas presented the longest median OS while no patients refined as CNS neuroblastoma or HGG survived. CONCLUSIONS: Our study confirmed that DNA methylation profiling provides relevant information for the classification of rare neoplasms like CNS embryonal tumors. Especially for selected cases with ambiguous histology, implementation of this tool should be considered to improve diagnostic precision and tailor patients’ management.