Epithelioid Soft Tissue Neoplasm of the Soft Palate with a PTCH1-GLI1 Fusion: A Case Report and Review of the Literature

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.

GLI1, CDK4, and MDM2 Co-Amplification Gastric Plexiform Fibromyxoma: A Case Report and Literature Review

Plexiform fibromyxoma (PF) is a rare mesenchymal tumor that primarily occurs in gastric origin with a benign behavior. PF commonly harbors the MALAT1::GLI1 fusion gene. Here, we describe a case of a 36-year-old female with a PF. Abdominal computed tomography (CT) showed a 3.3 cm mass in the stomach. She underwent laparoscopic partial gastrectomy. Immunohistochemistry (IHC) of the tumor revealed strongly positive staining for CD34, SDHB, STAT6, MDM2, and CDK4. And the tumor showed TP53 mutant expression. Next-generation sequencing (NGS) comprehensive genomic profiling identified GLI1, CDK4, and MDM2 co-amplification and TP53 mutations. Here, we first report a case of a young woman with a PF harboring co-amplification of GLI1, CDK4, and MDM2 genes. The patient underwent complete removal of the tumor without the use of radiotherapy or chemotherapy. No recurrence was observed during the follow-up period of 8 months. This study aims to improve our understanding of PF by analyzing the clinicopathological characteristics of this case, including immunohistochemical (IHC) and genetic examination, and reviewing relevant literature.

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 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.

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

BACKGROUND

GLI1 is a transcription factor protein that has recently gained recognition in a morphologically distinct group of epithelioid soft tissue tumors characterized by GLI1 fusions or amplifications. The head and neck region, particularly the tongue, is a common location for GLI1-altered tumors. DDIT3 break apart fluorescence in situ hybridization (FISH), commonly used to identify translocations in myxoid/round cell liposarcoma, has been used as a surrogate test to detect both fusions and amplifications of the 12q13.3 region encompassing DDIT3 and GLI1 gene loci.

METHODS

We herein report 5 cases of GLI1-altered soft tissue tumors. Three arose in the oropharynx (base of tongue/vallecula, tonsil) and two arose in the tongue. Given the frequent oropharyngeal location and epithelioid morphology, p16 immunohistochemistry was performed on cases with available material. Commercially available DDIT3 break apart FISH, custom GLI1 specific FISH, and RNA sequencing were performed on select cases.

RESULTS

Two cases showed amplification using DDIT3 FISH which was confirmed using GLI1 specific FISH. The remaining cases harbored ACTB::GLI1, one of which showed rearrangement of the 12q13.3 region by DDIT3 FISH with absence of amplification by GLI1 specific FISH. STAT6 immunoexpression was positive in the GLI1-amplified cases and negative in the GLI1-rearranged cases while MDM2 expression was positive in the 4 cases tested. CDK4 expression was strong and diffuse in the GLI1-amplified cases. p16 immunohistochemistry showed strong nuclear and cytoplasmic staining in 50-70% of tumor cells in all four tested cases.

CONCLUSION

Here we show that GLI1-altered soft tissue tumors are frequently positive for p16 and can occur in tonsillar regions of the oropharynx. As such, positive p16 immunohistochemistry alone cannot be used as evidence for the diagnosis of HPV-related squamous cell carcinoma as strong and diffuse p16 expression may also occur in GLI1-altered soft tissue tumors. Commercially available DDIT3 break apart FISH, which is readily available in many cytogenetic laboratories, may be useful as a sensitive surrogate test for GLI1 fusions and amplifications.

Proceedings of the North American Society of Head and Neck Pathology, Los Angeles, CA, March 20, 2022. Emerging Bone and Soft Tissue Neoplasms in the Head and Neck Region

In the past decade, several emerging bone and soft tissue neoplasms of the head and neck region have been described in the literature, including GLI1-altered mesenchymal tumors, (intraosseous) rhabdomyosarcoma with TFCP2 fusion, and adamantinoma-like Ewing sarcoma. This review provides a summary of the clinical features, histologic characteristics, immunoprofile, key diagnostic features, and differential diagnoses of these emerging entities. Notably, all three entities show epithelioid morphology and cytokeratin immunopositivity, highlighting the need to consider these mesenchymal neoplasms in the differential diagnoses of cytokeratin-positive epithelioid tumors in the head and neck region. Appropriate workups including detection of the characteristic molecular alterations are essential for the correct diagnosis.