[Neuroepithelial tumor with PATZ1 fusion - case report and focus on an ill-defined entity]. / Tumeur neuroépithéliale avec fusion PATZ1 ­ à propos d'un cas et mise au point sur une entité mal définie.

The neuroepithelial tumor with PATZ1 fusion is a recently described tumor type, at the border between central nervous system and mesenchymal tumors. The histopathological diagnosis of this neoplasm, not recognized by the 2021 WHO classification, is challenging due to its varied and non-specific morphologic features. Most cases are densely cellular with monomorphous nuclei. Perivascular pseudo-rosettes of the ependymal type and astroblastic features are frequent. Blood vessels may be hyalinized. The tumor may display low- or high-grade features. OLIG2 and GFAP are variably expressed. Guided by DNA methylation profiling, a pathologist aware of this tumor type will search for a fusion involving PATZ1 and EWSR1 or MN1. The physiopathology of neuroepithelial tumor with PATZ1 fusion is not fully understood. The prognosis appears to align with that of intermediate-grade tumors but follow-up data are scarce. The therapeutic management is often similar to that of high-grade neoplasms. Nonetheless, PATZ1 fusion is a potential therapeutic avenue that may lead to personalized and less aggressive treatments.

[Fusion genes in salivary gland tumors]. / Les tumeurs des glandes salivaires associées à des transcrits de fusion.

Salivary gland tumors represent a diagnostic challenge for pathologists due to their rarity, their very wide histopathological and immuno-phenotypic spectrum, and the recent identification of new entities. This article presents the main molecular characteristics of these tumors in order to allow any pathologist to perceive the diagnostic tracks of these ENT tumors and to better guide the molecular approach to establish the diagnosis and guide therapy.

Beneath HMGA2 alterations in Pleomorphic Adenomas: Pathological, Immunohistochemical, and Molecular Insights.

AIMS: Most salivary gland neoplasms are distinguished by specific recurrent gene fusions. Recently, a subset of pleomorphic adenomas (PAs) originated from the parotid gland harboring the HMGA2::WIF1 fusion was described with a canalicular adenoma-like morphology and a greater propensity for recurrence and carcinomatous transformation. METHODS AND RESULTS: This study delineates the clinicopathological attributes of 54 cases of PAs exhibiting HMGA2 alterations, predominantly characterized by the HMGA2::WIF1 fusion, alongside a comparative analysis of their morphological and immunohistochemical profiles. The cohort consisted of 23 females and 31 males (n=54), mean age was 56.7 (25-84), tumors predominantly originated from the parotid gland (94.4%, 51/54), with 3 cases from seromucous glands (5.6%). Mean tumor size was 2.6 cm (0.8-7.5). No clinical difference (demographic, follow-up) was observed among histological subsets (conventional, hybrid, and pure). Complete excision was performed in all cases, with follow-up data available for 41% (22/54) of patients, showing 13.6% of recurrence (3/22) between 5 and 8 months. Various histological growth patterns were identified, with the pure hypercellular monomorphic subset being the most prevalent. The HMGA2::WIF1 gene was identified in all subsets without any particular predominance. Novel gene partners of HMGA2 were identified, comprising NRXN1, INPP4B, MSRB3, PHLDA1, and FLJ41278. CONCLUSIONS: The present study reports that the HMGA2::WIF1 gene fusion was present in all subsets of PAs without significant predominance. However, further investigations are warranted to explore the relationship between histological subsets of PAs and the molecular alterations underlying them.

CNS tumors with PLAGL1-fusion: beyond ZFTA and YAP1 in the genetic spectrum of supratentorial ependymomas.

A novel methylation class, "neuroepithelial tumor, with PLAGL1 fusion" (NET-PLAGL1), has recently been described, based on epigenetic features, as a supratentorial pediatric brain tumor with recurrent histopathological features suggesting an ependymal differentiation. Because of the recent identification of this neoplastic entity, few histopathological, radiological and clinical data are available. Herein, we present a detailed series of nine cases of PLAGL1-fused supratentorial tumors, reclassified from a series of supratentorial ependymomas, non-ZFTA/non-YAP1 fusion-positive and subependymomas of the young. This study included extensive clinical, radiological, histopathological, ultrastructural, immunohistochemical, genetic and epigenetic (DNA methylation profiling) data for characterization. An important aim of this work was to evaluate the sensitivity and specificity of a novel fluorescent in situ hybridization (FISH) targeting the PLAGL1 gene. Using histopathology, immunohistochemistry and electron microscopy, we confirmed the ependymal differentiation of this new neoplastic entity. Indeed, the cases histopathologically presented as "mixed subependymomas-ependymomas" with well-circumscribed tumors exhibiting a diffuse immunoreactivity for GFAP, without expression of Olig2 or SOX10. Ultrastructurally, they also harbored features reminiscent of ependymal differentiation, such as cilia. Different gene partners were fused with PLAGL1: FOXO1, EWSR1 and for the first time MAML2. The PLAGL1 FISH presented a 100% sensitivity and specificity according to RNA sequencing and DNA methylation profiling results. This cohort of supratentorial PLAGL1-fused tumors highlights: 1/ the ependymal cell origin of this new neoplastic entity; 2/ benefit of looking for a PLAGL1 fusion in supratentorial cases of non-ZFTA/non-YAP1 ependymomas; and 3/ the usefulness of PLAGL1 FISH.