Embryonal tumor with abundant neuropil and true rosettes (ETANTR) with a focal amplification at chromosome 19q13.42 locus: further evidence of two new instances in China.

Recently, the term "embryonal tumor with multilayered rosettes" (ETMR), including embryonal tumor with abundant neuropil and true rosettes (ETANTR) and ependymoblastoma (EBL) as a distinct tumor entity, has become an important topic of discussion for neuropathologists since the discovery of a unique genomic alteration in 2009. Here, we contribute two new East Asian instances of ETANTR in a 29-month-old boy who underwent subtotal resection of a large tumor in the bilateral parieto-occipital lobes and a 4-year-old boy who underwent subtotal resection of the right midpontine neoplasm. Both tumors showed a typical histopathological pattern of hypercellular clusters of undifferentiated small cells and ependymoblastic rosettes admixed with paucicellular neuropil-like zones indicative for ETANTR. Rare Homer-Wright neuroblastic rosettes and papillary pseudorosettes, as well as enlarged lumina with mucinous material, were also observed. Immunohistological studies revealed that tumor cells in hypercellular and paucicellular zones were diffusely positive for microtubule-associated protein 2; ependymoblastic rosette cells stained with epithelial membrane antigen at the luminal membrane and exhibiting strong immunoreactivity with p53 protein. β-Catenin and Nestin were frequently detected in the hypercellular zones as well as in the ependymoblastic rosettes. Fluorescence in situ hypribization analysis revealed that both cases contained a unique focal amplification at the 19q13.42 chromosome locus and chromosome 2 polysomy. A new WHO classification of tumors of the CNS should be considered for these neoplasms with unique focal amplification at the 19q13.42 chromosome locus, based on the clinicopathological and molecular features of ETANTR that are distinct and reproducibly recognizable.