Recurrent novel THBS1-ADGRF5 gene fusion in a new tumor subtype "Acral FibroChondroMyxoid Tumors"

Calcified chondroid mesenchymal neoplasm: a clinicopathological and molecular analysis

AIMS

Calcified chondroid mesenchymal neoplasm (CCMN) is a recently identified category of soft tissue neoplasms defined by cartilage or cartilaginous matrix formation and FN1 gene fusions. Its rarity and similarities to other soft tissue tumours pose diagnostic challenges. This study aims to deepen understanding of CCMN, highlighting molecular pathology's role in diagnosis to reduce misdiagnosis, overdiagnosis and overtreatment.

METHODS

We conducted a clinicopathological analysis of five newly identified CCMN cases and reviewed 87 cases documented in PubMed. Next-generation sequencing was used to detect molecular alterations, while clinical, radiological and histopathological features were extensively reviewed.

RESULTS

CCMN typically affects adults, presenting as a slow-growing, painless mass in soft tissue. Histologically, CCMN exhibits a chondroid matrix with variable calcification. Molecular analyses in our cases identified FN1::FGFR1, FN1::FGFR2 and FN1::TEK fusions. Review of the 87 cases revealed consistent clinical, imaging and molecular profiles, underscoring CCMN's distinct characteristics.

CONCLUSIONS

CCMN should be considered in the differential diagnosis of soft tissue tumours with chondroid and calcified components. Detecting FN1 gene fusions aids in distinguishing CCMN from morphologically similar tumours.

Acral Fibrochondromyxoid Tumor: A Clinicopathologic and Molecular Genetic Study of 37 Cases

Acral fibrochondromyxoid tumor (AFCMT) is a recently described likely benign mesenchymal neoplasm arising in the distal extremities with distinctive histologic features and a recurrent THBS1::ADGRF5 fusion. We studied an additional 37 cases of AFCMT and expanded on the so-far reported clinicopathologic and molecular findings. Tumors occurred in 21 females and 16 males, ranging in age from 17 to 78 years (median age: 47), and solely involved the hands (24/37, 65%) or feet (13/37, 35%). Histologic examination revealed well-delineated uni- or multinodular tumors with prominent vasculature-rich septa and bland, chondrocyte-like tumor cells set within abundant chondromyxoid stroma. Immunohistochemical studies showed that tumor cells were positive for CD34 (25/27; 93%) and ERG (27/27; 100%), whereas negative for S100 protein (0/31). Molecular analysis revealed evidence of a THBS1::ADGRF5 fusion in 17 of 19 (89%) successfully tested tumors. Clinical follow-up was available in 8 cases (median: 97 months), with multiple local recurrences in 1 case at 276, 312, and 360 months. We conclude that AFCMT is a distinct entity with reproducible morphologic, immunohistochemical, and molecular genetic features that should be differentiated from other similar appearing acral mesenchymal neoplasms.

Recurrent Inflammatory Myofibroblastic Tumor of Larynx Harboring a Novel THBS1::ALK Fusion

Inflammatory myofibroblastic tumor (IMT) is a rare soft tissue tumor primarily occurring in the abdominopelvic region of young patients, and it is characterized by spindle-shaped myofibroblasts, or fibroblasts surrounded by inflammatory infiltrate. Herein, we report a case of a 24-year-old male with a firm submucosal mass in the anterior right vocal fold diagnosed as an IMT that recurred 14 months later. The tumor demonstrated a novel THBS1::ALK fusion containing Exons 1-7 of the thrombospondin 1 (THBS1) gene fused to Exon 19 of the anaplastic lymphoma kinase (ALK) gene via next-generation sequencing with the NextSeq sequencer. The fusion of THBS1 to ALK potentially results in increased expression and constitutive activation of the ALK kinase domain. These findings not only broaden the repertoire of known ALK fusion partners implicated in tumorigenesis but also provide a novel avenue for investigating the etiology of recurrent IMT by considering this fusion event as a causal factor. To our knowledge, this is the second case of IMT of the larynx with this novel mutation reported in the literature and the first such case with a detailed description of this specific fusion and clinical recurrence.

Comprehensive Molecular Characterization of a Large Series of Calcified Chondroid Mesenchymal Neoplasms Widening Their Morphologic Spectrum

Recently, FN1 fusions to receptor tyrosine kinase genes have been identified in soft tissue tumors with calcified chondroid matrix named calcifying chondroid mesenchymal neoplasms (CCMNs). We collected 33 cases of CCMN from the French network for soft tissue and bone tumors. We performed whole-exome RNA sequencing, expression analysis, and genome-wide DNA methylation profiling in 33, 30, and 20 cases of CCMN compared with a control group of tumors, including noncalcified tenosynovial giant cell tumor (TGCT). Among them, 15 cases showed morphologic overlap with soft tissue chondroma, 8 cases with tophaceous pseudogout, and 10 cases with chondroid TGCT. RNA-sequencing revealed a fusion of FN1 in 76% of cases (25/33) with different 5' partners, including most frequently FGFR2 (14 cases), TEK or FGFR1. Among CCMN associated with FGFR1 fusions, 2 cases had overexpression of FGF23 without tumor-induced osteomalacia. Four CCMN had PDGFRA::USP8 fusions; 3 of which had histologic features of TGCT and were located in the hip, foot, and temporomandibular joint (TMJ). All cases with FN1::TEK fusion were located at TMJ and had histologic features of TGCT with or without chondroid matrix. They formed a distinct cluster on unsupervised clustering analyses based on whole transcriptome and genome-wide methylome data. Our study confirms the high prevalence of FN1 fusions in CCMN. In addition, through transcriptome and methylome analyses, we have identified a novel subgroup of tumors located at the TMJ, exhibiting TGCT-like features and FN1::TEK fusions.

Calcified Chondroid Mesenchymal Neoplasms

Calcified chondroid mesenchymal neoplasms (CCMN) represent a morphologic spectrum of related tumors. Historically, chondroid matrix or chondroblastoma-like features have been described in soft tissue chondroma, tenosynovial giant cell tumors (especially of the temporomandibular joint (TMJ) region), and in a subset of tophaceous pseudogout. Recently, these tumors have been found to share FN1-receptor tyrosine kinase (RTK) fusions. This review discusses the clinical, morphologic, immunohistochemical, and molecular genetic features of CCMN. The distinction from morphologic mimics is also discussed.

Myoepithelioma, myoepithelioma-like, and chondroid soft-tissue tumors arising at acral sites: a review

Myoepithelial neoplasms comprise a histologically and immunophenotypically diverse spectrum of entities. The following review is a comprehensive summary of acral lesions demonstrating myoepithelial-like and chondroid histomorphology, as well as recently described mimics that are diagnostically challenging to distinguish. The salient clinicopathologic, immunophenotypic, and molecular features of each entity are described.

Calcified Chondroid Mesenchymal Neoplasm: Exploring the Morphologic and Clinical Features of an Emergent Entity With a Series of 33 Cases

Calcified chondroid mesenchymal neoplasm is a term proposed for tumors with a spectrum of morphologic features, including cartilage/chondroid matrix formation, that frequently harbor FN1 gene fusions. We report a series of 33 cases of putative calcified chondroid mesenchymal neoplasms, mostly referred for expert consultation out of concern for malignancy. Patients included 17 males and 16 females, with a mean age of 51.3 years. Anatomic locations include the hands and fingers, feet and toes, head and neck, and temporomandibular joint; 1 patient presented with multifocal disease. Radiologic review showed soft tissue masses with variable internal calcification, which occasionally scalloped bone but in all cases appeared indolent/benign. Tumors had a mean gross size of 2.1 cm and a homogenous rubbery to fibrous/gritty tan-white cut surface. Histology demonstrated multinodular architecture with a prominent chondroid matrix and increased cellularity towards the periphery of the nodules. The tumor cells were polygonal with eccentric nuclei and bland cytologic features and showed a variable amount of increased spindled / fibroblastic forms in the perinodular septa. The majority of cases had notable grungy and/or lacy calcifications. A subset of cases demonstrated at least focal areas of increased cellularity and osteoclast-like giant cells. Herein, we confirm the distinct morphologic and clinicopathologic features associated with this entity with the largest series to date, with a focus on practical diagnostic separation from similar chondroid neoplasms. Awareness of these features is critical in avoiding pitfalls, including a malignant diagnosis of chondrosarcoma.

The clinical relevance of the adhesion G protein-coupled receptor F5 for human diseases and cancers

Among the numerous adhesion G protein-coupled receptors (GPCRs), adhesion G protein-coupled estrogen receptor F5 (ADGRF5) contains unique domains in the long N-terminal tail which can determine cell-cell and cell-matrix interaction as well as cell adhesion. Nevertheless, the biology of ADGRF5 is complex and still poorly explored. Accumulating evidence suggests that the ADGRF5 activity is fundamental in health and disease. For instance, ADGRF5 is essential in the proper function of lungs and kidney as well as the endocrine system, and its signification in vascularization and tumorigenesis has been demonstrated. The most recent studies have provided findings about the diagnostic potential of ADGRF5 in osteoporosis and cancers, and ongoing studies suggest other diseases as well. Here, we elaborate on the current state of knowledge about the ADGRF5 in the physiology and pathophysiology of human diseases and highlight its high potential as a novel target in various therapeutic areas.

Clinicopathologic and Molecular Study of Hybrid Nerve Sheath Tumors Reveals Their Common Association With Fusions Involving VGLL3

A subset of benign peripheral nerve sheath tumors are "hybrid" combining several lines of differentiation, most often schwannian and perineurial features. The pathogenesis of these tumors was poorly described until the recent discovery of recurrent VGLL3 rearrangements in hybrid schwannoma/perineuriomas, supporting the hypothesis that this entity represents a distinct subgroup of tumors and not only a morphologic variation of other peripheral nerve sheath tumors. Following this finding, we investigated 10 cases of hybrid peripheral nerve sheath tumors with immunohistochemistry, RNA sequencing, and array comparative genomic hybridization. By light microscopy, 7 tumors were hybrid schwannoma/perineurioma tumors, and 3 were hybrid schwannoma/neurofibroma. Most cases of hybrid schwannoma/perineuriomas displayed VGLL3 rearrangements fused in 5' either to CHD7 or CHD9 (n=6/7) and had simple diploid genetic profiles with few copy number alterations. Compared with a control group composed of 28 tumors associated with varied neural phenotypes, all VGLL3-fused tumors clustered together by transcriptomic analysis. In contrast, 1 case of hybrid schwannoma/perineurioma tumor harbored a CDH9-ZFHX3 fusion, a prominent perineurial component identified by immunohistochemistry and clustered with perineuriomas. No recurrent genetic alteration was seen in the 3 hybrid schwannoma/neurofibromas. To summarize, this study confirms and expands the recent findings on hybrid schwannoma/perineurioma, highlighting the predominance of VGLL3 fusions in these tumors.

[Soft tissue tumours with FN1 (Fibronectin 1) fusion gene]

Translocations involving FN1 gene have been described in several tumours, which share the presence of a cartilaginous matrix with or without calcifications and a good prognosis. They encompass: soft tissue chondroma, synovial chondromatosis, calcifying aponeurotic fibroma, phosphaturic mesenchymal tumour and a new spectrum of tumours: "the calcified chondroid mesenchymal neoplasms". We review all the clinical, histopathological and molecular data of these tumours and discuss the differential diagnoses.

Wholistic approach - transcriptomic analysis and beyond using archival material for molecular diagnosis

Many neoplasms remain unclassified after histopathological examination, which requires further molecular analysis. To this regard, mesenchymal neoplasms are particularly challenging due to the combination of their rarity and the large number of subtypes, and many entities still lack robust diagnostic hallmarks. RNA transcriptomic profiles have proven to be a reliable basis for the classification of previously unclassified tumors and notably for mesenchymal neoplasms. Using exome-based RNA capture sequencing on more than 5000 samples of archival material (FFPE), the combination of expression profiles analyzes (including several clustering methods), fusion genes, and small nucleotide variations has been developed at the Centre Léon Bérard (CLB) in Lyon for the molecular diagnosis of challenging neoplasms and the discovery of new entities. The molecular basis of the technique, the protocol, and the bioinformatics algorithms used are described herein, as well as its advantages and limitations.

Acral FibroChondroMyxoid tumor: imaging features of a new entity

"Acral FibroChondroMyxoid tumor" (AFCMT) is a recently described distinctive subtype of acral soft tissue tumor that typically arises on the fingers and toes. We herein present the unreported imaging features of AFCMT in a 44-year-old woman. This otherwise healthy patient was referred for a painful, slow-growing, soft tissue mass in the middle finger of her right hand. Initial radiographs and computed tomography showed a small lesion centered in the soft tissue of the ulnar aspect of the proximal phalanx, associated with scalloping of the underlying bone. Magnetic resonance imaging confirmed the presence of a well-circumscribed soft tissue tumor that exhibited relatively high T2-weighted signal intensity and marked enhancement after contrast administration. Subsequent excisional biopsy was performed. Histologically, the tumor was characterized by an abundant stroma displaying fibrous, chondroid, and myxoid areas. By immunohistochemistry, tumor cells stained for CD34, ERG, and focally S100 protein. RNA-sequencing allowed detection of THBS1-ADGFR5 gene fusion which confirmed the diagnosis of AFCMT. At 2-year follow-up, the patient remains free of recurrence. AFCMT is a previously unrecognized entity that may mimic chondroma and should be considered in the differential diagnosis of soft tissue tumors with cartilaginous or myxoid stroma in the extremities.