Expanding the spectrum of GLI1-altered mesenchymal tumors-A high-grade uterine sarcoma harboring a novel PAMR1::GLI1 fusion and literature review of GLI1-altered mesenchymal neoplasms of the gynecologic tract

GLI1-altered Mesenchymal Tumor - Multi-omic Characterization of a Case Series and Patient-level Meta-analysis of 167 cases for Risk Stratification

GLI1-altered mesenchymal tumors have recently emerged as a distinctive group of neoplasms characterized by GLI1 fusions or amplifications. While there is clearly metastatic potential, the clinicopathological 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 to 68). They arose from 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 partner 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 median follow-up of 30 months (range 17.3 to 102 months), and one 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 clinicopathological 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 predicting 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 which 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.

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.

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.

Emerging mesenchymal tumour types and biases in the era of ubiquitous sequencing

New tumour types are being described at increasing frequency, and most new tumour types are now identified via retrospective review of next-generation sequencing data. This contrasts with the traditional, morphology-based method of identifying new tumour types, and while the sequencing-based approach has accelerated progress in the field, it has also introduced novel and under-recognised biases. Here, we discuss tumour types identified based on morphology, including superficial CD34-positive fibroblastic tumour, pseudoendocrine sarcoma and cutaneous clear cell tumour with melanocytic differentiation and ACTIN::MITF fusion. We also describe tumour types identified primarily by next-generation sequencing, including epithelioid and spindle cell rhabdomyosarcoma, round cell neoplasms with EWSR1::PATZ1 fusion, cutaneous melanocytic tumour with CRTC1::TRIM11 fusion, clear cell tumour with melanocytic differentiation and MITF::CREM fusion and GLI1-altered mesenchymal neoplasms, including nested glomoid neoplasm.

Gastroblastoma Treated by Endoscopic Submucosal Excavation with a Novel PTCH1::GLI2 Fusion: A Rare Case Report and Literature Review

Gastroblastoma is an extremely rare stomach tumor that primarily presents in adolescent and early adulthood, with a biphasic cell morphology of epithelioid and spindle cells. In light of its similarity to other childhood blastomas, it has been named gastroblastoma. Few patients showed a potential of metastasis and recurrence, however, most of the reported cases were alive, with no evidence of the disease after surgical treatment. Commonly, MALAT1-GLI1 fusion has been considered to be the most relevant mutation. Herein, we present a case of an asymptomatic 58-year-old man who happened to find a submucosal gastric mass during a gastroscope and received endoscopic submucosal excavation (ESE). He turned out to have a gastroblastoma with a novel PTCH1::GLI2 fusion confirmed by Sanger sequencing. The patient was discharged two days after ESE without any complication and was recurrence-free during his one-year follow-up. According to the previous literature and our own experience, in cases with characteristic histopathology and immunohistochemistry patterns, a diagnosis of gastroblastoma should be considered even without a MALAT1-GLI1 fusion. Gastroblastoma pursues a favorable clinical outcome and endoscopic therapy could be an effective alternative treatment choice.