GLI1-Altered Soft Tissue Tumors of the Head and Neck: Frequent Oropharyngeal Involvement, p16 Immunoreactivity, and Detectable Alterations by DDIT3 Break Apart FISH

Expanding the Spectrum of GLI1-rearranged Neoplasms of the Gastrointestinal Tract to Include Monophasic Keratin-positive Epithelial Neoplasms

GLI1-altered tumors form a diverse group occurring in various anatomic locations. In the alimentary tract, the most established are gastroblastoma, a biphasic epithelial-mesenchymal neoplasm of the stomach, and plexiform fibromyxoma, a pure spindle cell neoplasm. The spectrum of GLI1-rearranged gastrointestinal tumors has recently expanded with reports of cases in other parts of the GI tract, some exhibiting gastroblastoma-like features and others being pure mesenchymal neoplasms. These tumors often display a nonspecific immunophenotype, with only CD56 and cyclin D1 expression being common. Biphasic GLI1-altered tumors show diffuse keratin positivity in the epithelial component only, and GLI1-altered mesenchymal tumors typically lack or show only focal keratin expression. This study details 2 GLI1-rearranged gastrointestinal tract tumors with diffuse keratin and CD56 expression, composed entirely of epithelial cells with a nested growth pattern and finely stippled monotonous nuclei, leading to an initial suspicion of neuroendocrine tumor in both cases, despite lack of synaptophysin and chromogranin expression. Diffuse strong nuclear cyclin D1 expression was seen in both cases, and conversely, strong cyclin D1 staining was only seen in 5.4% (4/74) of well-differentiated neuroendocrine tumors tested. These 2 GI tract neoplasms highlight a widened spectrum of GLI1-rearranged tumors, now including monophasic epithelial neoplasms with diffuse keratin expression.

Malignant epithelioid neoplasm with GLI1 gene rearrangement (PANX3::GLI1 transcript) and MDM2 gene amplification

We hereby report the case of an epithelioid neoplasm arising from pterygopalatine fossa in a 13-year-old child harboring PANX3::GLI1 fusion and MDM2 amplification. Identified chimeric gene can explain observed signs of osteogenic differentiation. We discuss the challenges in differential diagnosis from osteogenic tumors and soft tissue neoplasms with epithelioid morphology. Our case is the first report of a tumor with such genetic abnormalities and it is about to replenish the spectrum of rare GLI1-rearranged tumors.

GLI1-Altered Mesenchymal Tumor-Multiomic Characterization of a Case Series and Patient-Level Meta-analysis of One Hundred Sixty-Seven Cases for Risk Stratification

GLI1-altered mesenchymal tumors have recently emerged as a distinctive group of neoplasms characterized by GLI1 fusions or amplifications. Although there is clearly metastatic potential, the clinicopathologic features predicting for metastasis are currently unknown. Herein, we present 6 cases of GLI1-altered mesenchymal tumors with multiomics analysis. The median patient age was 50 years (range, 3-68 years). They arose from the extremities and trunk (2/6), head and neck region (2/6), and gastrointestinal tract (2/6). Histologically, they featured uniform round to ovoid cells with nested architecture and a rich vascular network. One case displayed abundant multinucleated giant cells. All stained positive for GLI1 (5/5) and CD56 (6/6). Molecularly, they featured GLI1 fusion (5/6) and amplification (1/6). Fusion partners included ACTB (3/5), TXNIP (1/5), and novel TUBA1B (1/5). Multiomics analysis revealed they possessed distinct expression and epigenomic profiles. All the 6 cases had follow-up information, with 5 of them having no evidence of disease at a median follow-up of 30 months (range, 17.3-102 months), and 1 case being died of disease with regional neck lymph node and bilateral lung metastasis at 81.5 months of follow-up. By incorporating cases reported in the literature, we analyzed clinicopathologic features of a total of 167 cases predictive of malignant behavior. We found that size ≥6 cm and mitotic count ≥5 per 10 high-power fields are predictive of metastasis. Cases with both high-risk features had significantly poorer survival. This study expands the literature database of GLI1-altered mesenchymal tumors and identifies features that can be used for risk stratification.

A Comprehensive Clinicopathologic and Molecular Reappraisal of GLI1 -altered Mesenchymal Tumors with Pooled Outcome Analysis Showing Poor Survival in GLI1 - amplified Versus GLI1- rearranged Tumors

GLI1 -altered mesenchymal tumor is a recently described distinct pathologic entity with an established risk of malignancy, being defined molecularly by either GLI1 gene fusions or amplifications. The clinicopathologic overlap of tumors driven by the 2 seemingly distinct mechanisms of GLI1 activation is still emerging. Herein, we report the largest series of molecularly confirmed GLI1 -altered mesenchymal neoplasms to date, including 23 GLI1- amplified and 15 GLI1 -rearranged new cases, and perform a comparative clinicopathologic, genomic, and survival investigation. GLI1- rearranged tumors occurred in younger patients (42 vs. 52 y) and were larger compared with GLI1 -amplified tumors (5.6 cm vs. 1.5 cm, respectively). Histologic features were overall similar between the 2 groups, showing a multinodular pattern and a nested architecture of epithelioid, and less commonly spindle cells, surrounded by a rich capillary network. A distinct whorling pattern was noted among 3 GLI1 -amplified tumors. Scattered pleomorphic giant cells were rarely seen in both groups. The immunoprofile showed consistent expression of CD56, with variable S100, CD10 and SMA expression. Genomically, both groups had overall low mutation burdens, with rare TP53 mutations seen only in GLI1- amplified tumors. GLI1 -amplified mesenchymal tumors exhibit mostly a single amplicon at the 12q13-15 locus, compared with dedifferentiated liposarcoma, which showed a 2-peak amplification centered around CDK4 (12q14.1) and MDM2 (12q15). GLI1 -amplified tumors had a significantly higher GLI1 mRNA expression compared with GLI1 -rearranged tumors. Survival pooled analysis of current and published cases (n=83) showed a worse overall survival in GLI1 -amplified patients, with 16% succumbing to disease compared with 1.7% in the GLI1- rearranged group. Despite comparable progression rates, GLI1 -amplified tumors had a shorter median progression-free survival compared with GLI1 -rearranged tumors (25 mo vs. 77 mo). Univariate analysis showed that traditional histologic predictors of malignancy (mitotic count ≥4/10 high-power fields, presence of necrosis, and tumor size ≥5 cm) are associated with worse prognosis among GLI1 -altered mesenchymal tumors.

Unique case of a GLI1 amplified biphasic mesenchymal tumor of the orbit

GLI1-altered mesenchymal tumors are an emerging entity in soft tissue pathology. In the head and neck region, they are most commonly in the tongue. Limited published data indicate a propensity for local recurrence, regional spread, and distant metastasis in both GLI1-rearranged and GLI1-amplified tumors. The purpose of this report is to present the rare case of a GLI1-amplified spindle cell tumor of the orbit and a focused review of the literature. A 54-year-old woman presented with proptosis, eye pain, and ocular motility restriction in the left eye. Imaging demonstrated a tumor occupying the superomedial intraconal orbit that was distinct from the extraocular muscles, optic nerve, and globe. The tumor was totally resected with a combined open transorbital and endoscopic, endonasal approach. Pathological analysis demonstrated a spindled and epithelioid mesenchymal tumor with diffuse nuclear GLI1 expression. PCR-based, next*-generation sarcoma fusion panel was negative for GLI1 fusions, including GLI1::ACTB fusions; however, DDIT3 breaks apart fluorescence in situ hybridization (FISH), which can be used as a surrogate for GLI1 alterations due to proximity to 12q13.3, showing amplification. Post-operatively, the patient had recovered visual acuity. She received adjuvant radiation therapy (60 Gy in 30 fractions). Surveillance for recurrence, regional spread, and distant metastasis has been negative at a 6-month follow-up. Ultimately, we report the first case of a GLI1-amplified mesenchymal neoplasm of the intraconal orbit managed with gross total resection via a combined approach followed by adjuvant radiation therapy.

GLI1-Altered Soft Tissue Tumor in the Tongue-A Case Report and Literature Review

Background: Soft tissue tumors with fusions or amplifications of the GLI1 gene have distinctive molecular characteristics and have recently been considered a unique pathological entity, thus named "GLI1-altered soft tissue tumors." It is a rare mesenchymal neoplasm that involves soft tissues at any site. Case presentation: We report an example of this condition in a 13-year-old Chinese male patient who presented with a mass in the tongue. The tumor was multilobulated; the tumor cells were arranged in nests and sheets, had a rich, delicate fibrovascular network, and were separated by a hyalinized fibrous stroma. The tumor cells were epithelioid to ovoid, with variable eosinophilic to pale vacuolated cytoplasm and round to oval nuclei. Immunostaining revealed that the tumor cells were positive for CDK4 and CD56. Fluorescence in situ hybridization (FISH) for GLI1 translocation was positive, with a high level of amplification of the translocated segment. Literature review: We present a comprehensive literature review of this condition, focusing on its clinical presentation, histological features, immunohistochemical profile, molecular characteristics, and prognosis.

GLI1 Coamplification in Well-Differentiated/Dedifferentiated Liposarcomas: Clinicopathologic and Molecular Analysis of 92 Cases

GLI1(12q13.3) amplification is identified in a subset of mesenchymal neoplasms with a distinct nested round cell/epithelioid phenotype. MDM2 and CDK4 genes are situated along the oncogenic 12q13-15 segment, amplification of which defines well-differentiated liposarcoma (WDLPS)/dedifferentiated liposarcoma (DDLPS). The 12q amplicon can occasionally include GLI1, a gene in close proximity to CDK4. We hereby describe the first cohort of GLI1/MDM2/CDK4 coamplified WD/DDLPS. The departmental database was queried retrospectively for all cases of WD/DDLPS having undergone next-generation (MSK-IMPACT) sequencing with confirmed MDM2, CDK4, and GLI1 coamplification. Clinicopathologic data was obtained from a review of the medical chart and available histologic material. Four hundred eighty-six WD/DDLPS cases underwent DNA sequencing, 92 (19%) of which harbored amplification of the GLI1 locus in addition to that of MDM2 and CDK4. These included primary tumors (n = 60), local recurrences (n = 29), and metastases (n = 3). Primary tumors were most frequently retroperitoneal (47/60, 78%), mediastinal (4/60, 7%), and paratesticular (3/60, 5%). Average age was 63 years, with a male:female ratio of 3:2. The cohort was comprised of DDLPS (86/92 [93%], 6 of which were WDLPS with early dedifferentiation) and WDLPS without any longitudinal evidence of dedifferentiation (6/92, 7%). One-fifth (13/86, 17%) of DDLPS cases showed no evidence of a well-differentiated component in any of the primary, recurrent, or metastatic specimens. Dedifferentiated areas mostly showed high-grade undifferentiated pleomorphic sarcoma-like (26/86,30%) and high-grade myxofibrosarcoma-like (13/86,16%) morphologies. A disproportionately increased incidence of meningothelial whorls with/without osseous metaplasia was observed as the predominant pattern in 16/86 (19%) cases, and GLI1-altered morphology as described was identified in a total of 10/86 (12%) tumors. JUN (1p32.1), also implicated in the pathogenesis of WD/DDLPS, was coamplified with all 3 of MDM2, CDK4, and GLI1 in 7/91 (8%) cases. Additional loci along chromosomal arms 1p and 6q, including TNFAIP3, LATS1, and ESR1, were also amplified in a subset of cases. In this large-scale cohort of GLI1 coamplified WD/DDLPS, we elucidate uniquely recurrent features including meningothelial whorl-like and GLI-altered morphology in dedifferentiated areas. Assessment of tumor location (retroperitoneal or mediastinal), identification of a well-differentiated liposarcoma component, and coamplification of other spatially discrete genomic segments (1p and 6q) might aid in distinction from tumors with true driver GLI1 alterations.

The value of GLI1 and p16 immunohistochemistry in the premolecular screening for GLI1-altered mesenchymal neoplasms

Mesenchymal neoplasms with GLI1 alterations have recently been reported in several anatomic locations. Their morphology and immunohistochemistry (IHC) are nonspecific, making their recognition a true challenge. To assess the diagnostic value of GLI1 and p16 IHC for identifying GLI1-altered neoplasms, we evaluated 12 such neoplasms (6 GLI1-amplified and 6 with GLI1-fusions) using the GLI1 IHC. Additionally, we evaluated some of their morphological and molecular mimickers, including glomangiomas, Ewing sarcomas (ES), myxoid liposarcomas, and MDM2/CDK4-amplified sarcomas (well-differentiated liposarcoma/WDLPS, dedifferentiated liposarcoma/DDLPS, and intimal sarcoma). All successfully tested GLI1-altered tumors (11/11) demonstrated at least moderate/strong nuclear and/or cytoplasmic GLI1 IHC positivity. GLI1-amplified tumors exhibited a moderate/strong predominantly nuclear staining, compared to a moderate, patchy, and predominantly cytoplasmic GLI1 positivity in GLI1-fusion tumors. Among their mimics, GLI1 immunoreactivity, either cytoplasmic or nuclear, was observed in intimal sarcoma (3/3) and WDLPS/DDLPS (22/25). GLI1 IHC demonstrated 92% sensitivity and 90.8% specificity in diagnosing GLI1-altered neoplasms. Strong/moderate nuclear/cytoplasmic p16 immunoexpression was noted in all GLI1-amplified tumors compared to none of fused cases. Overall, the GLI1/p16 combination demonstrated a sensitivity and specificity of 100% and 93% for GLI1-amplified tumors. In conclusion, we confirm that GLI1 IHC represents a good, quick, and cheap helpful screening tool. The inclusion of p16 may aid in pre-screening for potential GLI1-amplified neoplasms and provide insights on which tumors warrant further molecular testing.

Gene of the month: DDIT3

DNA damage-inducible transcript 3 (DDIT3) gene, mapped to the human chromosome 12q13.3, encodes a protein that belongs to the CCAAT/enhancer-binding protein family of transcription factors. DDIT3 is involved in the proliferative control that responds to endoplasmic reticulum stress in normal conditions, dimerising other transcription factors with basic leucine zipper (bZIP) structural motifs. DDIT3 plays a significant role during cell differentiation, especially adipogenesis, arresting the maturation of adipoblasts. In disease, FUS/EWSR1::DDIT3 fusion is the pathogenic event that drives the development of myxoid liposarcoma. The amplification of DDIT3 in other adipocytic neoplasms mediates the presence of adipoblast-like elements. Another fusion, GLI1::DDIT3, has rarely been documented in other tumours. This paper reviews the structure and function of DDIT3, its role in disease-particularly cancer-and its use and pitfalls in diagnostic testing, including immunohistochemistry as a tissue-based marker.

GLI1-Altered Mesenchymal Tumors

GLI1-altered mesenchymal tumors comprise an emerging group of neoplasms characterized by fusions or amplifications involving GLI1, a gene that encodes a key regulator of the Hedgehog signaling pathway. In recent years, tumors with GLI1 alterations have been reported across a variety of anatomic sites and a broad age range. Although these tumors can exhibit a wide morphologic spectrum and a variable immunophenotype, they frequently present with monomorphic ovoid cells arranged in distinctive nests with a rich, arborizing vascular network. Recent evidence indicates that they have the potential to metastasize, which suggests that they may be best considered a sarcoma.

GLI1-Altered Mesenchymal Tumors With ACTB or PTCH1 Fusion: A Molecular and Clinicopathologic Analysis

Mesenchymal tumors with GLI1 fusions or amplifications have recently emerged as a distinctive group of neoplasms. The terms GLI1-altered mesenchymal tumor or GLI1-altered soft tissue tumor serve as a nosological category, although the exact boundaries/criteria require further elucidation. We examined 16 tumors affecting predominantly adults (median age: 40 years), without sex predilection. Several patients had tumors of longstanding duration (>10 years). The most common primary site was soft tissue (n = 9); other sites included epidural tissue (n = 1), vertebra (n = 1), tongue (n = 1), hard palate (n = 1), and liver (n = 1). Histologically, the tumors demonstrated multinodular growth of cytologically uniform, ovoid-to-epithelioid, occasionally short spindled cells with delicate intratumoral vasculature and frequent myxoid stroma. Mitotic activity ranged from 0 to 8 mitoses/2 mm2 (mean 2). Lymphovascular invasion/protrusion of tumor cells into endothelial-lined vascular spaces was present or suspected in 6 cases. Necrosis, significant nuclear pleomorphism, or well-developed, fascicular spindle-cell growth were absent. Half demonstrated features of the newly proposed subset, "distinctive nested glomoid neoplasm." Tumors were consistently positive for CD56 (n = 5/5). A subset was stained with S100 protein (n = 7/13), SMA (n = 6/13), keratin (n = 2/9), EMA (n = 3/7), and CD99 (n = 2/6). Tumors harbored ACTB::GLI1 (n = 15) or PTCH1::GLI1 (n = 1) fusions. The assays used did not capture cases defined by GLI1 amplification. We also identified recurrent cytogenetic gains (1q, 5, 7, 8, 12, 12q13.2-ter, 21, and X). For patients with available clinical follow-up (n = 8), half were disease free. Half demonstrated distant metastases (lungs, bone, or soft tissue). Of cases without follow-up (n = 8), 2 were known recurrences, and 1 was presumed metastasis. Our results imply a more aggressive biological potential than currently reported. Given the possibility for metastasis and disease progression, even in cytologically bland, nested tumors, close clinical surveillance, akin to that for sarcoma management, may be indicated. The term GLI1-altered mesenchymal tumor with malignant potential is proposed.

Soft Tissue Sarcomas with Chromosomal Alterations in the 12q13-15 Region: Differential Diagnosis and Therapeutic Implications

The chromosomal region 12q13-15 is rich in oncogenes and contains several genes involved in the pathogenesis of various mesenchymal neoplasms. Notable genes in this region include MDM2, CDK4, STAT6, DDIT3, and GLI1. Amplification of MDM2 and CDK4 genes can be detected in various mesenchymal and nonmesenchymal neoplasms. Therefore, gene amplification alone is not entirely specific for making a definitive diagnosis and requires the integration of clinical, radiological, morphological, and immunohistochemical findings. Neoplasms with GLI1 alterations may exhibit either GLI1 rearrangements or amplifications of this gene. Despite the diagnostic implications that the overlap of genetic alterations in neoplasms with changes in genes within the 12q13-15 region could create, the discovery of coamplifications of MDM2 with CDK4 and GLI1 offers new therapeutic targets in neoplasms with MDM2/CDK4 amplification. Lastly, it is worth noting that MDM2 or CDK4 amplification is not exclusive to mesenchymal neoplasms; this genetic alteration has also been observed in other epithelial neoplasms or melanomas. This suggests the potential use of MDM2 or CDK4 inhibitors in neoplasms where alterations in these genes do not aid the pathological diagnosis but may help identify potential therapeutic targets. In this review, we delve into the diagnosis and therapeutic implications of tumors with genetic alterations involving the chromosomal region 12q13-15, mainly MDM2, CDK4, and GLI1.

Small biopsies in the head and neck: Bone and soft tissue

Bone and soft tissue lesions in the head and neck encompass not only a broad morphologic spectrum but also significant inherent clinicopathologic overlap. Epidemiology, radiology, and location - similar to the diagnostic assessment in other sites - are especially important considerations in the context of an established mesenchymal proliferation. Herein, the approach towards diagnosis is stratified by morphology (spindle, sarcomatoid, epithelioid, round cell), cellular lineage (fibroblastic, nerve sheath, rhabdomyogenic), and tumor grade (benign, low- to high-grade malignant) as the basis of further immunohistochemical or molecular investigation.