YAP1-TFE3 epithelioid hemangioendothelioma: a case without vasoformation and a new transcript variant

Vascular tumors of intermediate malignancy: An update

The term "hemangioendothelioma" is used for endothelial neoplasms of intermediate malignancy and describes a group of rare neoplasms having biologic behavior falling in between that of the benign hemangiomas and fully malignant angiosarcomas. The hemangioendotheliomas fall into several specific, clinicopathologically and genetically distinct entities, specifically epithelioid hemangioendothelioma, kaposiform hemangioendothelioma, papillary intralymphatic angioendothelioma and retiform hemangioendothelioma (hobnailed hemangioendothelioma), pseudomyogenic hemangioendothelioma, composite hemangioendothelioma, and YAP1::TFE3-fused hemangioendothelioma. The clinical, morphologic, immunohistochemical, and genetic features, and the differential diagnosis of each of these rare entities are discussed in this review.

Clear cell stromal tumor of the lung with multinucleated giant cells: a report of a case with YAP1-TFE3 fusion

BACKGROUND

Clear cell (hemangioblastoma-like) stromal tumor of the lung (CCSTL) is a rare pulmonary neoplasm. Recently, 9 cases of CCSTL harboring the YAP1-TFE3 gene fusion have been described, and it has been suggested that this aberration could be a characteristic feature of this tumor.

CASE PRESENTATION

We here report another case of CCSTL in a 57-year-old male, which presented as a solitary lung nodule 45 mm in the greatest dimension. Microscopically, the tumor consisted of epithelioid to spindled cells with mild-to-moderate nuclear atypia, finely granular or vesicular chromatin, and small nucleoli. Nuclear indentations were a common finding. There were up to 3 mitoses per 10 HPF. The cytoplasm was slightly eosinophilic or clear. Scattered non-tumor large multinucleated cells were present. Immunohistochemically, the tumor cells showed diffuse positivity for TFE3, CD10, vimentin, and IFITM1. Other markers examined were negative, and the expression of lineage-specific markers was not found. NGS analysis revealed a fusion transcript of the YAP1 and TFE3 genes, and a pathogenic variant of the MUTYH gene.

CONCLUSION

Our finding supports the recent data suggesting that CCSTL represents a distinct entity characterized by the recurrent YAP1-TFE3 fusion.

Unraveling the Biology of Epithelioid Hemangioendothelioma, a TAZ-CAMTA1 Fusion Driven Sarcoma

Simple Summary

Epithelioid hemangioendothelioma (EHE) is a rare vascular cancer that involves a gain-of-function gene fusion involving TAZ, a transcriptional coactivator, and one of two end effectors of the Hippo pathway. Although the activity of TAZ and/or YAP, a paralog of TAZ, is consistently altered in many cancers, genetic alterations involving YAP/TAZ are rare, and the precise mechanisms by which YAP/TAZ are activated are not well understood in most cancers. Because WWTR1(TAZ)–CAMTA1 is the only genetic alteration in approximately half of EHE, EHE is a genetically clean and homogenous system for understanding how the dysregulation of TAZ promotes tumorigenesis. Therefore, by using EHE as a model system, we hope to elucidate the essential biological pathways mediated by TAZ and identify mechanisms to target them. The findings of EHE research can be applied to other cancers that are addicted to high YAP/TAZ activity.

Abstract

The activities of YAP and TAZ, the end effectors of the Hippo pathway, are consistently altered in cancer, and this dysregulation drives aggressive tumor phenotypes. While the actions of these two proteins aid in tumorigenesis in the majority of cancers, the dysregulation of these proteins is rarely sufficient for initial tumor development. Herein, we present a unique TAZ-driven cancer, epithelioid hemangioendothelioma (EHE), which harbors a WWTR1(TAZ)–CAMTA1 gene fusion in at least 90% of cases. Recent investigations have elucidated the mechanisms by which YAP/TAP-fusion oncoproteins function and drive tumorigenesis. This review presents a critical evaluation of this recent work, with a particular focus on how the oncoproteins alter the normal activity of TAZ and YAP, and, concurrently, we generate a framework for how we can target the gene fusions in patients. Since EHE represents a paradigm of YAP/TAZ dysregulation in cancer, targeted therapies for EHE may also be effective against other YAP/TAZ-dependent cancers.

Primary Intranodal Epithelioid Hemangioendothelioma with Molecular Confirmation

Epithelioid hemangioendothelioma (EHE) is a rare low-grade malignant vascular tumor with indolent biology, characterized by reciprocal t(1;3)(p36.6;q25) with resultant WWTR1::CAMTA1 gene fusion in the vast majority of cases, regardless of anatomic location. Only a small subset, exhibiting well formed vasoformative features will contain YAP1::TFE3 gene fusion. Primary intranodal EHE is exquisitely rare. We report a case in a 54-year-old male with persistent left groin mass with discomfort for nine months. A CT of the abdomen and pelvis showed a minimally enlarged left inguinal lymph node measuring 2.8 cm with no other masses or lymphadenopathy. PET/CT and MRI imaging of the abdomen showed no evidence of disease elsewhere. Sections showed an epithelioid vasoformative neoplasm, centrally necrotic and involving a lymph node. The cells were arranged in anastomosing cords with intracytoplasmic lumens, resembling "signet ring cells". By immunohistochemistry, the tumor cells were positive for vimentin, CD31, CD34, ERG and CAMTA1; and negative for AE1/3, CAM 5.2, KRT7, KRT20, desmin, actin, HMB-45 and S-100. Ki-67 proliferation index was estimated at <1%. Molecular studies including next generation sequencing (NGS) revealed the presence of WWTR1::CAMTA1 gene fusion, and fluorescence in situ hybridization for CAMTA1 (1p36.23) and WWTR1 (3p25.1) showed fusion signals, diagnostic of EHE. We highlight a rare occurrence of EHE in a lymph node exhibiting morphologic mimicry with metastatic carcinoma.

A YAP1::TFE3 cutaneous low-grade fibromyxoid neoplasm: A novel entity!

Cutaneous fibromyxoid neoplasms (CFMN) comprise a vast category of benign and malignant tumors that include, but are not limited to, low-grade fibromyxoid sarcoma, myxofibrosarcoma, myxoid dermatofibrosarcoma protuberans, myxoid solitary fibrous tumor, and myxoid neurofibroma with differing implications for treatment and prognosis. Herein, a case of CFMN arising as a painless, slow-growing, flesh-colored forearm mass in a 53-year-old female is presented. The neoplasm comprised of copious myxoid material with banal spindle cells, exhibiting mild hyperchromasia, dissecting the dermal collagen table. Focal perivascular accentuation of spindle cells was identified in the absence of vasoformative features. Immunohistochemically, lesional cells were strongly and diffusely positive for CD34 and multifocally for Factor XIIIa and epithelial membrane antigen while negative for CD31, ERG, FLI-1, D2-40, smooth muscle actin, Desmin, S100, HMB-45, STAT6, MUC4, and keratins. RNA- and DNA-sequencing identified a YAP1::TFE3 fusion transcript that were subsequently corroborated by fluorescence in situ hybridization and immunohistochemistry for TFE3 (Xp11.23) locus rearrangement and strong, diffuse TFE3 immunoreactivity, respectively. To date, the YAP1::TFE3 fusion has only been identified in a subset of epithelioid hemangioendotheliomas and clear cell stromal tumors of the lung. This is the first report of a CFMN featuring a YAP1::TFE3 fusion (YAP1 Exon 1 and TFE3 Exon 4). The morphologic findings are unlike those previously described for epithelioid hemangioendothelioma and suggest that this neoplasm may represent a yet unclassified or novel CFMN entity. Although the patient is 1-year status postsurgical excision with no evidence of clinical recurrence, the clinical behavior of this novel entity remains to be fully characterized.

YAP1-TFE3-fused hemangioendothelioma: a multi-institutional clinicopathologic study of 24 genetically-confirmed cases

YAP1-TFE3-fused hemangioendothelioma is an extremely rare malignant vascular tumor. We present the largest multi-institutional clinicopathologic study of YAP1-TFE3-fused hemangioendothelioma to date. The 24 cases of YAP1-TFE3-fused hemangioendothelioma showed a female predominance (17 female, 7 male) across a wide age range (20-78 years old, median 44). Tumors were most commonly located in soft tissue (50%), followed by bone (29%), lung (13%), and liver (8%), ranging from 3 to 115 mm in size (median 40 mm). About two-thirds presented with multifocal disease, including 7 cases with distant organ metastasis. Histopathologically, we describe three dominant architectural patterns: solid sheets of coalescing nests, pseudoalveolar and (pseudo)vasoformative pattern, and discohesive strands and clusters of cells set in a myxoid to myxohyaline stroma. These patterns were present in variable proportions across different tumors and often coexisted within the same tumor. The dominant cytomorphology (88%) was large epithelioid cells with abundant, glassy eosinophilic to vacuolated cytoplasm, prominent nucleoli and well-demarcated cell borders. Multinucleated or binucleated cells, prominent admixed erythrocytic and lymphocytic infiltrates, and intratumoral fat were frequently present. Immunohistochemically, ERG, CD31, and TFE3 were consistently expressed, while expression of CD34 (83%) and cytokeratin AE1/AE3 (20%) was variable. CAMTA1 was negative in all but one case. All cases were confirmed by molecular testing to harbor YAP1-TFE3 gene fusions: majority with YAP1 exon 1 fused to TFE3 exon 4 (88%), or less commonly, TFE3 exon 6 (12%). Most patients (88%) were treated with primary surgical resection. Over a follow-up period of 4-360 months (median 36 months) in 17 cases, 35% of patients remained alive without disease, and 47% survived many years with stable, albeit multifocal and/or metastatic disease. Five-year progression-free survival probability was 88%. We propose categorizing YAP1-TFE3-fused hemangioendothelioma as a distinct disease entity given its unique clinical and histopathologic characteristics in comparison to conventional epithelioid hemangioendothelioma.

Vascular Tumors of Bone: Updates and Diagnostic Pitfall

Vascular tumors of bone can be diagnostically challenging because of their rarity and histologic overlap with diverse mimics. Vascular tumors of bone can be categorized as benign (hemangioma), intermediate-locally aggressive (epithelioid hemangioma), intermediate-rarely metastasizing (pseudomyogenic hemangioendothelioma), and malignant (epithelioid hemangioendothelioma and angiosarcoma). Recurrent genetic alterations have been described, such as FOSB rearrangements in pseudomyogenic hemangioendothelioma and a subset of epithelioid hemangiomas; CAMTA1 or TFE3 rearrangements in epithelioid hemangioendothelioma. This review discusses the clinical, histologic, and molecular features of vascular tumors of bone, along with diagnostic pitfalls and strategies for avoidance.

Gene fusions in vascular tumors and their underlying molecular mechanisms

INTRODUCTION

The group of vascular tumors contains many different entities, and is considered difficult by pathologists, as they often have overlapping histological characteristics. Chromosomal translocations have been identified in ~20% of mesenchymal tumors and are considered the drivers of tumor formation. Many translocations have been discovered over the past decade through next-generation sequencing. This technological advancement has also revealed several recurrent gene fusions in vascular tumors.

AREAS COVERED

This review will discuss the various vascular tumors for which recurrent gene fusions have been identified. The gene fusions and the presumed molecular mechanisms underlying tumorigenesis are shown, and potential implications for targeted therapies discussed. The identification of these gene fusions in vascular tumors has improved diagnostic accuracy, especially since several of these fusions can be easily detected using surrogate immunohistochemical markers.

EXPERT OPINION

The identification of gene fusions in a subset of vascular tumors over the past decade has improved diagnostic accuracy, and has provided the pathologists with novel diagnostic tools to accurately diagnose these often difficult tumors. Moreover, the increased understanding of the underlying molecular mechanisms can guide the development of targeted therapeutic strategies.

YAP1-TFE3 gene fusion variant in clear cell stromal tumour of lung: report of two cases in support of a distinct entity

AIMS

Clear cell (haemangioblastoma-like) stromal tumour of the lung is a newly described, rare pulmonary neoplasm. Recurrent YAP1-TFE3 gene fusions have recently been reported in three cases. We describe two additional cases and confirm the characteristic YAP1-TFE3 gene fusion.

METHODS AND RESULTS

Two mesenchymal tumours of lung were identified from our soft tissue pathology consultation services and RNA sequencing was performed. Both cases were in male patients, aged 35 and 77 years. Both presented as solitary lung nodules measuring 3.9 and 7.5 cm in greatest dimension. Histopathologically, the tumours were composed of epithelioid to plump spindle cells arranged in packets and solid sheets. The cells showed fusiform to ovoid nuclei with open chromatin, variably prominent nucleoli and scant to moderate, clear to eosinophilic cytoplasm. Cytological atypia and significant mitotic activity were minimal. None of the tumours expressed lineage-specific immunophenotypical markers. Both cases were diffusely positive for nuclear TFE3. Unlike YAP1-TFE3-fused epithelioid haemangioendothelioma, for which the fusion breakpoint occurs in YAP1 exon 1 and TFE3 exons 4 or 6, the fusion breakpoints of these tumours were located in YAP1 exon 4 and TFE3 exon 7. Following complete surgical resection, neither of the tumours has recurred or metastasised (follow-up period 6-7 months).

CONCLUSIONS

We validate the presence of YAP1-TFE3 gene fusion in a unique primary mesenchymal tumour of lung, adding additional support for clear cell stromal tumour of the lung as a distinct entity.

TFE3 rearranged epithelioid hemangioendothelioma of bone: A clinicopathological, immunohistochemical and molecular study of two cases

Epithelioid hemangioendothelioma (EHE) is a rare malignant angiocentric vascular neoplasm. Around 90% of classic EHE has a t(1;3)(p36;q25) that results in a WWTR1-CAMTA1 fusion gene, a histologically distinctive subset of EHE has been recently shown to have a t(10;14)(p13;q42)that results in a different fusion gene, YAP1-TFE3. Twenty-one cases of TFE3 Rearranged Epithelioid Hemangioendothelioma have been reported in the literature, and only two cases occurred in bone. In the report, we report additional two cases occurred in the femur and skull and review the related literature.

Multicentric visceral epithelioid hemangioendothelioma, with extremity dermal deposits, unusual late recurrence on the nasal bridge, and TFE3 gene rearrangement

Epithelioid hemangioendothelioma (EHE) is a malignant neoplasm with vascular differentiation that most frequently occurs within soft tissues, bone, lung, and liver. It is histologically typified by epithelioid or spindle cells present singly or in cords or clusters, many with cytoplasmic vacuoles that can contain intraluminal erythrocytes (in keeping with primitive vascular differentiation), within myxohyaline or sclerotic matrix. Up to 50% present with synchronous lesions as multifocal disease. The WWTR1-CAMTA1 fusion has been demonstrated in EHEs at a variety of sites and is considered to represent its genetic hallmark. We describe a case of EHE in a patient who initially presented with multiple liver and pulmonary deposits, was found to have a soft tissue lesion in the foot, and then presented with further lesions on the nasal bridge and the arm approximately 6 years after initial presentation. Interestingly, the case showed diffuse CAMTA1 expression but negative TFE3 immunohistochemically, but in contrast showed TFE3 gene rearrangement with fluorescence in situ hybridization but no evidence of WWTR1-CAMTA1 translocation. The clinical behavior of EHE is unpredictable, and this case highlights unusual anatomic, immunohistochemical, and molecular cytogenetic findings. Characterization of the genetics of EHE is important because targeted therapies toward products of the specific WWTR1-CAMTA1 gene fusion may have an impact in the near future.

Hepatic epithelioid haemangioendothelioma: Report of one case

Hepatic epithelioid hemangioendothelioma (EHE) is a rare vascular tumor with malignant biological behavior, which is frequently missed or misdiagnosed. Its diagnosis relies mainly on histological and immunohistochemical studies. Surgical resection is the main treatment. Here we report a case of hepatic EHE and performed a review of the relevant literature.