GNA11 and N-RAS mutations: alternatives for MAPK pathway activating GNAQ mutations in primary melanocytic tumours of the central nervous system.

AIM: Primary melanocytic tumours are uncommon neoplasms of the central nervous system. Although similarities with uveal melanomas have been hypothesized, data on their molecular features are limited. METHODS: In this study, we investigated the mutational status of BRAF(V600E) , KIT, GNAQ, GNA11, N-RAS and H-RAS in a series of 19 primary melanocytic tumours of the central nervous system (CNS). RESULTS: We identified six cases harbouring mutations in the hotspot codon 209 of the GNAQ gene and two cases with mutations in the hotspot codon 209 of the GNA11 gene. Two mutations in codon 61 of N-RAS were also found. In the single strand conformation polymorphism (SSCP) analysis, no shifts corresponding to BRAF(V600E) mutations or suggesting activating mutations in the KIT gene were observed. CONCLUSIONS: In primary melanocytic tumours of the CNS, GNA11 and N-RAS mutations represent a mechanism of MAPK pathway activation alternative to the common GNAQ mutations. On the other hand, BRAF(V600E) mutations and activating KIT mutations seem to be absent or very rare in these tumours.

TP53, ß-Catenin and c-myc/N-myc status in embryonal tumours with ependymoblastic rosettes.

BACKGROUND: The primitive neuroectodermal tumours of central nervous system (CNS-PNET) are a heterogeneous group of neoplasms, occurring in the CNS and composed of undifferentiated or poorly differentiated neuroepithelial cells which may display divergent differentiation along neuronal, astrocytic and ependymal lines. The WHO classification includes in this group of tumours also ependymoblastomas and medulloepitheliomas. Several groups have reported examples of CNS-PNET with combined histological features of ependymoblastoma and neuroblastoma, defined as 'embryonal tumour with abundant neuropil and true rosettes'. The presence of the amplification of chromosome region 19q13.42, common in both ependymoblastoma and embryonal tumour with abundant neuropil and true rosettes, suggests that they represent a histological spectrum of a single biological entity. METHODS: We examined 24 cases of ependymoblastoma/embryonal tumour with abundant neuropil and true rosettes (EPBL/ETANTR) for the presence of mutations of TP53 and ß-Catenin and for amplification of c-myc/N-myc. RESULTS: The single strand conformation polymorphism-mutational screening did not identify any mutation in exons 5 to 8 of the TP53 gene. However, we found a point mutation affecting codon 34 (GGA → GTA) of ß-Catenin gene resulting in a Glycine → Valine substitution. No cases presented c-myc/N-myc amplification. CONCLUSIONS: EPBL/ETANTRs show molecular features different from other CNS-PNET and medulloblastomas. The presence of alterations in the ß-Catenin/WNT pathway seems to be noteworthy due to the close relationship between this pathway and miR-520g encoded in chromosome 19q13.42 region amplified in these tumours.