Translocation t(1;3)(p36.3;q25) is a nonrandom aberration in epithelioid hemangioendothelioma

Epithelioid hemangioendothelioma-its history, clinical features, molecular biology and current therapy

Epithelioid hemangioendothelioma (EHE) is a remarkably rare tumor arising from endothelial cells that is classified as a vascular tumor in the WHO classification. The tumor is predominantly characterized by the presence of fusion genes, such as WWTR1-CAMTA1 or YAP1-TFE3, with a minority of cases exhibiting other rare fusion genes. EHE exhibits a broad age of onset, typically presenting at ~50 years, but it is not uncommon in pediatric populations. It manifests in a variety of organs, including the liver, lung, soft tissue and bone. Initial multiple-organ involvement is also observed. The tumor's biological behavior and prognosis vary substantially based on the primary site of manifestation. From a therapeutic perspective, initial active surveillance might be considered in selected cases, although surgical intervention remains the mainstay of treatment, especially for localized single-organ involvement. Chemotherapy is administered to patients with progressive unresectable tumors. Recent advances in the biological analysis of EHE fusion genes have elucidated their diverse functions. Additionally, next-generation sequencing has facilitated the identification of other mutations beyond the fusion genes. These continuous efforts to understand the biology of the fusion genes themselves and/or the dysregulated signaling by fusion genes are expected to lead to the development of novel therapeutic strategies for EHE. This article aims to provide a comprehensive review of EHE, encompassing its historical context, clinical manifestations, molecular biology and the current state of treatment.

Update on immunohistochemistry in bone and soft tissue tumors: Cost-effectively replacing molecular testing with immunohistochemistry

Soft tissue tumors form part of a challenging domain in diagnostic pathology owing to their comparative rarity, astonishing histologic diversity, and overlap between entities. Many of these tumors are now known to be defined by highly recurrent, or, in some instances, unique molecular alterations. Insights from gene profiling continue to elucidate the wider molecular landscape of soft tissue tumors; many of these advances have been co-opted by immunohistochemistry (IHC) for diagnostic applications. There now exists a multitude of antibodies serving as surrogate markers of recurrent gene fusions, amplifications, and point mutations, which, in certain settings, can replace the need for more resource and time-intensive cytogenetic and molecular genetic analyses. IHC presents many advantages including rapid turnaround time, cost-effectiveness, and interpretative reproducibility. A sensible application of these immunohistochemical markers complemented by a working knowledge of the molecular pathogenesis of bone and soft tissue tumors permits accurate diagnosis in the majority of cases. In this review, we will outline some of these biomarkers while emphasizing molecular correlates and highlighting interpretative challenges and pitfalls.

Primary vascular tumors of bone: A comprehensive literature review on classification, diagnosis and treatment

Primary vascular tumors of bone are a heterogeneous group of neoplasms, ranging from benign hemangiomas to frankly malignant epithelioid hemangioendotheliomas and angiosarcomas. Over the years, their classification has been a matter of discussion, due to morphologic similarities and uncertainty regarding biologic behavior. Over the past decade, with the development of next-generation sequencing, there has been a significant improvement in the molecular characterization of these lesions. The integration of their morphologic, immunohistochemical and molecular features has led to a better stratification, with important prognostic and therapeutic implications. Nevertheless, primary vascular bone tumors still represent a challenge for medical oncologists. Given their rarity and heterogeneity, in the last few years, there has been no significant progress in medical treatment options, so further research is needed. Here we present a review of the current knowledge regarding primary vascular tumors of the bone, correlating clinicopathologic features with tumor behavior and therapeutic approaches.

Mesenchymal tumours of the pleura: review and update

Primary mesenchymal tumours of the pleura are uncommon and can be diagnostically challenging due to their overlapping histopathologic and immunophenotypic features. Herein we discuss selected mesenchymal tumours of the pleura, including solitary fibrous tumour, calcifying fibrous tumour, desmoid fibromatosis, synovial sarcoma, schwannoma, malignant peripheral nerve sheath tumour, inflammatory myofibroblastic tumour, follicular dendritic cell sarcoma, epithelioid hemangioendothelioma, and desmoplastic small round cell tumour. We review their clinicopathologic characteristics, along with an update on the relevant immunohistochemical and molecular features.

The oncogenic fusion protein TAZ::CAMTA1 promotes genomic instability and senescence through hypertranscription

TAZ::CAMTA1 is a fusion protein found in over 90% of Epithelioid Hemangioendothelioma (EHE), a rare vascular sarcoma with an unpredictable disease course. To date, how TAZ::CAMTA1 initiates tumour formation remains unexplained. To study the oncogenic mechanism leading to EHE initiation, we developed a model system whereby TAZ::CAMTA1 expression is induced by doxycycline in primary endothelial cells. Using this model, we establish that upon TAZ::CAMTA1 expression endothelial cells rapidly enter a hypertranscription state, triggering considerable DNA damage. As a result, TC-expressing cells become trapped in S phase. Additionally, TAZ::CAMTA1-expressing endothelial cells have impaired homologous recombination, as shown by reduced BRCA1 and RAD51 foci formation. Consequently, the DNA damage remains unrepaired and TAZ::CAMTA1-expressing cells enter senescence. Knockout of Cdkn2a, the most common secondary mutation found in EHE, allows senescence bypass and uncontrolled growth. Together, this provides a mechanistic explanation for the clinical course of EHE and offers novel insight into therapeutic options.

Mesenchymal Neoplasms of the Liver

Mesenchymal neoplasms of the liver can be diagnostically challenging, particularly on core needle biopsies. Here, I discuss recent updates in neoplasms that are specific to the liver (mesenchymal hamartoma, undifferentiated embryonal sarcoma, calcifying nested stromal-epithelial tumor), vascular tumors of the liver (anastomosing hemangioma, hepatic small vessel neoplasm, epithelioid hemangioendothelioma, angiosarcoma), and other tumor types that can occur primarily in the liver (PEComa/angiomyolipoma, inflammatory pseudotumor-like follicular dendritic cell sarcoma, EBV-associated smooth muscle tumor, inflammatory myofibroblastic tumor, malignant rhabdoid tumor). Lastly, I discuss metastatic sarcomas to the liver, as well as pitfalls presented by metastatic melanoma and sarcomatoid carcinoma.

Hepatic epithelioid hemangioendothelioma-a single-institution experience with 51 cases

Objectives

The aim of the present study was to describe the experience at a single institution in the management of hepatic epithelioid hemangioendothelioma (HEHE).

Methods

We included 51 patients with histologically confirmed HEHE. We performed log-rank (Cox-Mantel) survival analyses using Kaplan-Meier methods to test differences in survival between patients in different groups. Univariate Cox regression analyses and multivariate proportional hazards regression model were carried out to identify independent prognostic factors.

Results

Different imaging modalities were used to diagnose HEHE with various presentations. Liver resection (LR), liver transplantation (LT), systemic treatment (ST), and surveillance had been used in our study. A significant difference was noted between the LR group and the surveillance group with respect to mean survival (p = 0.006), as was in the LR group and the ST group (p = 0.036), and in surgical approach (LR and LT) and nonsurgical approach (ST and surveillance) (p = 0.008). The mean survival between the ST group and the surveillance group was not significantly different (p = 0.851). LR (p = 0.010) and surgical approach (p = 0.014) were favorable predictors of outcome, while macrovascular invasion (MaVI) (p = 0.037), lung metastasis (p = 0.040), and surveillance (p = 0.033) were poor prognostic factors in univariate analysis. Multivariate analysis showed that LR (p = 0.010) and surgical approach (p = 0.014) were independently associated with good OS, while surveillance (p = 0.033) was independently associated with poor OS. After adjusting for confounding factors, patients in the LR group have much better OS than those in the surveillance group (p = 0.013). However, there was no significant difference in OS between the LR group and ST group (p = 0.254), as was in the ST group and the surveillance group (p = 0.857).

Conclusions

The definitive diagnosis of HEHE was dependent on histopathology, and it was not possible to make a specific diagnosis without biopsy because the radiological findings were similar to those in some hepatic malignancies. ST was not recommended for patients who were not candidates for surgical approaches, and surgical approaches should be warranted regardless of disease stage. The retrospective nature and the small size of the data limited the generalizability of the study, designing a worldwide database that contains all data about patients with HEHE independent of their therapy, which was highly recommended.

Current Model Systems for Investigating Epithelioid Haemangioendothelioma

Epithelioid haemangioendothelioma (EHE) is a rare sarcoma of the vascular endothelium with an unpredictable disease course. EHE tumours can remain indolent for long period of time but may suddenly evolve into an aggressive disease with widespread metastases and a poor prognosis. Two mutually exclusive chromosomal translocations define EHE tumours, each involving one of the transcription co-factors TAZ and YAP. The TAZ-CAMTA1 fusion protein results from a t(1;3) translocation and is present in 90% of EHE tumours. The remaining 10% of EHE cases harbour a t(X;11) translocation, resulting in the YAP1-TFE3 (YT) fusion protein. Until recently, the lack of representative EHE models made it challenging to study the mechanisms by which these fusion proteins promote tumorigenesis. Here, we describe and compare the recently developed experimental approaches that are currently available for studying this cancer. After summarising the key findings obtained with each experimental approach, we discuss the advantages and limitations of these different model systems. Our survey of the current literature shows how each experimental approach can be utilised in different ways to improve our understanding of EHE initiation and progression. Ultimately, this should lead to better treatment options for patients.

Case report: Surgical treatment of a primary giant epithelioid hemangioendothelioma of the spine with total en-bloc spondylectomy

Background

Epithelioid hemangioendothelioma (EHE) is an extremely uncommon malignant neoplasm that originates from vascular endothelial or pre-endothelial cells. In this report, we present the case of patient who was diagnosed with a primary giant EHE of the spine and underwent treatment with total en-bloc spondylectomy (TES).

Case presentation

A 43-year-old male patient with a history of he presented to our hospital with chronic and progressive back pain. Physical examination revealed weakened sensation of acupuncture and touch on the left costal arch, while relatively normal neurological functions were preserved. Radiological examinations identified a giant destructive soft tissue lesion occupying the T8 vertebral region, with moderate destruction of the pedicle and lamina, as well as the 7th left rib. A preoperative biopsy of the 8th vertebra resulted in a diagnosis of epithelioid hemangioendothelioma(EHE). Postoperative immunohistochemical and pathological reports confirmed the presence of EHE in the left ribs and T8 ribs. The patient underwent resection of the 7th left rib and posterior pedicle screw fixation with 8 pairs of screws and a titanium mesh cage. Subsequently, thoracic en bloc spondylectomy was performed on the T8 vertebra. The patient did not receive radiation or chemotherapy following surgery. Over a period of 3 years, the patient remained free of disease and relapse.

Conclusion

The use of transarterial embolization with spherical embolic agents (TES) has been demonstrated to be a safe, effective, and reliable treatment option for hepatic epithelioid hemangioendothelioma (EHE). Nevertheless, it is crucial to conduct long-term follow-up of this patient in order to assess their clinical outcome.

The Recent Advances in Molecular Diagnosis of Soft Tissue Tumors

Soft tissue tumors are rare mesenchymal tumors with divergent differentiation. The diagnosis of soft tissue tumors is challenging for pathologists owing to the diversity of tumor types and histological overlap among the tumor entities. Present-day understanding of the molecular pathogenesis of soft tissue tumors has rapidly increased with the development of molecular genetic techniques (e.g., next-generation sequencing). Additionally, immunohistochemical markers that serve as surrogate markers for recurrent translocations in soft tissue tumors have been developed. This review aims to provide an update on recently described molecular findings and relevant novel immunohistochemical markers in selected soft tissue tumors.

Genetic Alterations and Deregulation of Hippo Pathway as a Pathogenetic Mechanism in Bone and Soft Tissue Sarcoma

The Hippo pathway is an evolutionarily conserved modulator of developmental biology with a key role in tissue and organ size regulation under homeostatic conditions. Like other signaling pathways with a significant role in embryonic development, the deregulation of Hippo signaling contributes to oncogenesis. Central to the Hippo pathway is a conserved cascade of adaptor proteins and inhibitory kinases that converge and regulate the activity of the oncoproteins YAP and TAZ, the final transducers of the pathway. Elevated levels and aberrant activation of YAP and TAZ have been described in many cancers. Though most of the studies describe their pervasive activation in epithelial neoplasms, there is increasing evidence pointing out its relevance in mesenchymal malignancies as well. Interestingly, somatic or germline mutations in genes of the Hippo pathway are scarce compared to other signaling pathways that are frequently disrupted in cancer. However, in the case of sarcomas, several examples of genetic alteration of Hippo members, including gene fusions, have been described during the last few years. Here, we review the current knowledge of Hippo pathway implication in sarcoma, describing mechanistic hints recently reported in specific histological entities and how these alterations represent an opportunity for targeted therapy in this heterogeneous group of neoplasm.

Treatment modalities and long-term outcomes of hepatic hemangioendothelioma in the United States

BACKGROUND

We analyzed the outcomes of patients with hepatic epithelioid hemangioendothelioma (HEHE) in the United States after stratification by their most definitive treatment.

METHODS

The National Cancer Data Base was used to identify patients with HEHE between 2004 and 2018. Patients were divided in four treatment groups: no surgical therapy, ablation, liver resection or liver transplantation. Demographics and clinical characteristics were compared, and Kaplan Meier functions and Cox-regression were used for unadjusted and adjusted survival analyses.

RESULTS

Among a total of 334 patients, 218 (65.2%) were managed non-surgically, 74 (22.1%) underwent hepatic resections, 35 (10.4%) underwent liver transplantation and 7 (2.1%) underwent ablations. The overall median survival was 111 months (95%CI 73-149) after liver transplantation, 69 months (95%CI 45-92) after hepatic resection, 38 months (95%CI 0-78) after ablation and 80 months (95%CI 70-90) for patients managed by watchful waiting (P < 0.001). After adjustment, patients who underwent liver transplantation were found to have a better survival when compared to other therapies (Hazard Ratio: 0.61, 95% Confidence Interval: 0.38-0.97, p = 0.035).

CONCLUSIONS

This study reports the outcomes of the largest cohort of patients with HEHE. The longest survival was observed after liver transplantation, followed by non-surgical management and hepatic resection. Because of selection bias, future studies to better characterize what criteria should be used for the selection of treatment modalities for HEHE are urgently needed.

Primary malignant epithelioid hemangioendothelioma of the pleura: A review and report of a novel case

Epithelioid hemangioendothelioma is considered an uncommon tumor originating from vascular tissues. Although this disease is an extremely rare malignant cancer, its pleural subtype is even less common. We discuss a 68-year-old man with isolated pleural epithelioid hemangioendothelioma, along with a literature review of all similar cases.

Epithelioid Hemangioendothelioma with WWTR1-CAMTA1 Fusion in the Parotid Gland Presenting as Bell’s Palsy

Epithelioid hemangioendothelioma is a rare tumor of endothelial differentiation most commonly arising in soft tissue, liver, and lung, following a variable clinical course. Most cases are characterized by a t(1;3)(p36;q23-25) resulting in WWTR1-CAMTA1 fusion. Only five epithelioid hemangioendothelioma have been previously reported arising in the salivary glands. None have presented as Bell’s palsy. In the current case, a 37-year-old female presented with a longstanding complaint of pain and fullness in the right preauricular region and progressive episodes of Bell’s palsy and facial nerve weakness. Surgical resection showed a tumor comprised of atypical cells with occasional intracytoplasmic vacuoles in a fibromyxoid stroma. Immunohistochemical stains demonstrated the neoplastic cells expressed ERG, CD31, and CD34, confirming vascular differentiation. Fluorescence in situ hybridization revealed a t(1;3)(p36;q25), confirming a diagnosis of epithelioid hemangioendothelioma. At 12-month follow-up, the patient has no evidence of disease.

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.

A novel WWTR1 :: AFF2 fusion in an intra‐abdominal soft tissue sarcoma with associated endometriosis

Application of molecular testing in clinical practice has led to significant advances in the classification of soft tissue sarcomas. Despite remarkable progress, there are still challenging cases that remain unclassified. In this study, we present an unusual spindle cell sarcoma arising in the abdominal cavity of a 37-year-old female. An extensive panel of immunostains was nonspecific for a line of differentiation and the tumor was subjected to targeted RNA sequencing for further classification. The findings showed a novel WWTR1::AFF2 fusion, which was further confirmed by break-apart FISH analysis for WWTR1 gene rearrangement. The tumor was attached to the wall of sigmoid colon and showed a highly cellular proliferation of plump spindle to epithelioid cells arranged in intersecting fascicles. Areas of extensive endometriosis were identified adjacent to the tumor. The immunoprofile was significant for reactivity with desmin, calponin, WT-1, ER, and PR, while negative for CD10, SMA, caldesmon, pan-keratin, ALK, CD117, and S100. The patient is alive and well after 11 months of follow-up. The exact histogenesis of this sarcoma remains unclear, however, the presence of adjacent endometriosis and coexpression of WT1/ER/PR raises the possibility of an unusual endometrioid stromal sarcoma, occurring outside the GYN tract. Additional cases are needed to establish the recurrent potential of this fusion event and to better define its pathogenesis and clinical behavior.

Diagnosis of epithelioid hemangioendothelioma eight days postpartum: Is there a link with pregnancy? A case report and review of the literature

Epithelioid hemangioendothelioma (EHE) is a rare and heterogeneous malignant vascular tumor. Decision making on a treatment strategy is difficult and a standard of care does not exist. EHE shows a wide age distribution but is rare in children. It can appear anywhere in the body, although lung and liver involvement are most common. There is a female predominance for visceral lesions and several case reports in which EHE developed during or after pregnancy are described in literature, hinting towards a putative role of sex hormones in the course of the disease. We present a case of a 32-year-old woman diagnosed with symptomatic pulmonary metastatic hepatic EHE (HEHE) 8 days postpartum, while the patient was completely asymptomatic before. A wait and see policy was chosen and the patient became asymptomatic in the months following the diagnosis. Although no expression of estrogen and progesterone receptors was found in the diagnostic liver biopsy specimen, we presume that the increased level of sex hormones during pregnancy may have triggered disease progression. The clinical behaviour of the disease in this case report reinforces the suspicion of female hormonal involvement in this type of malignancy and hints toward the potential role of other pregnancy-related factors, e.g. placental growth factor (PlGF), in the development of the disease.

Diagnosis of soft tissue tumors using immunohistochemistry as a surrogate for recurrent fusion oncoproteins

Soft tissue neoplasms encompass a broad spectrum of clinicopathologic manifestations. In a subset of soft tissue tumors, spanning a wide range of clinical behavior from indolent to highly aggressive, recurrent genetic translocations yield oncogenic fusion proteins that drive neoplastic growth. Beyond functioning as primary mechanisms of tumorigenesis, recurrent translocations represent key diagnostic features insofar as the presence of a particular oncogenic gene fusion generally points to specific tumor entities. In addition to more direct methods for identifying recurrent translocations, such as conventional cytogenetics or fluorescence in situ hybridization, immunohistochemistry for a component of the fusion oncoprotein increasingly is being used as a surrogate marker, exploiting the tendency of these fusion components to be distinctively overexpressed by translocation-bearing tumor cells. Diagnostic immunohistochemistry can also be used to identify the characteristic gene expression changes that occur downstream of oncogenic fusions. Here, we review the use of immunohistochemistry to detect surrogate markers of recurrent translocations in soft tissue tumors, focusing on the practical applications and limitations of this diagnostic approach.

Loss of expression of YAP1 C-terminus as an ancillary marker for epithelioid hemangioendothelioma variant with YAP1-TFE3 fusion and other YAP1-related vascular neoplasms

Epithelioid hemangioendothelioma (EHE) with YAP1-TFE3 fusion is a recently characterized distinctive variant of EHE that accounts for a small subset (<5%) of cases. It is composed of nests of epithelioid cells with voluminous pale cytoplasm and often shows focally vasoformative architecture. TFE3 immunohistochemistry (IHC) can be used to support the diagnosis; however, studies have questioned its specificity. Yes-associated protein 1 (YAP1), part of the Hippo signaling pathway, is expressed in normal endothelial cells, but becomes disrupted in EHE variant with YAP1-TFE3, such that only a small N-terminal region of YAP1 is expressed in the fusion protein. A recent study also reported YAP1 rearrangements in a subset of retiform and composite hemangioendotheliomas (RHE and CHE). In this study, we evaluated the diagnostic utility of an antibody directed against the C-terminus of YAP1 (YAP1-CT) for EHE with YAP1-TFE3, RHE, and CHE. In total, 78 tumors were included in the study: EHE variant with YAP1-TFE3 (n = 13), conventional (CAMTA1-positive) EHE (n = 20), pseudomyogenic hemangioendothelioma (n = 10), epithelioid hemangioma (n = 19), epithelioid angiosarcoma (n = 10), RHE (n = 4), and CHE (n = 2). IHC was performed using a rabbit monoclonal anti-YAP1 C-terminus antibody. EHE variant showed complete loss of YAP1-CT expression in 10 of 13 (77%) cases. All cases of RHE and CHE, with previously confirmed YAP1 rearrangements, also showed loss of YAP1-CT expression. Loss of YAP1-CT was seen in one conventional EHE (1/20; 5%). All other epithelioid vascular tumors showed retained YAP1-CT expression. Loss of expression of YAP1-CT appears to be associated with good sensitivity and specificity for EHE variant with YAP1-TFE3 fusion and may provide additional support along with TFE3 and CAMTA1 IHC in challenging cases. This marker may also be useful in the diagnosis of RHE and CHE.

Fusion Oncoproteins in Childhood Cancers: Potential Role in Targeted Therapy

Cancer remains the leading cause of death from disease in children. Historically, in contrast to their adult counterparts, the causes of pediatric malignancies have remained largely unknown, with most pediatric cancers displaying low mutational burdens. Research related to molecular genetics in pediatric cancers is advancing our understanding of potential drivers of tumorigenesis and opening new opportunities for targeted therapies. One such area is fusion oncoproteins, which are a product of chromosomal rearrangements resulting in the fusion of different genes. They have been identified as oncogenic drivers in several sarcomas and leukemias. Continued advancement in the understanding of the biology of fusion oncoproteins will contribute to the discovery and development of new therapies for childhood cancers. Here we review the current scientific knowledge on fusion oncoproteins, focusing on pediatric sarcomas and hematologic cancers, and highlight the challenges and current efforts in developing drugs to target fusion oncoproteins.

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.

WWTR1(TAZ)-CAMTA1 gene fusion is sufficient to dysregulate YAP/TAZ signaling and drive epithelioid hemangioendothelioma tumorigenesis

Epithelioid hemangioendothelioma (EHE) is a genetically homogenous vascular sarcoma that is a paradigm for TAZ dysregulation in cancer. EHE harbors a WWTR1(TAZ)-CAMTA1 gene fusion in >90% of cases, 45% of which have no other genetic alterations. In this study, we used a first of its kind approach to target the Wwtr1-Camta1 gene fusion to the Wwtr1 locus, to develop a conditional EHE mouse model whereby Wwtr1-Camta1 is controlled by the endogenous transcriptional regulators upon Cre activation. These mice develop EHE tumors that are indistinguishable from human EHE clinically, histologically, immunohistochemically, and genetically. Overall, these results demonstrate unequivocally that TAZ-CAMTA1 is sufficient to drive EHE formation with exquisite specificity, as no other tumor types were observed. Furthermore, we fully credential this unique EHE mouse model as a valid preclinical model for understanding the role of TAZ dysregulation in cancer formation and for testing therapies directed at TAZ-CAMTA1, TAZ, and YAP/TAZ signaling.

Hepatic epithelioid hemangioendothelioma: Update on diagnosis and therapy

With an estimated incidence of only 1-2 cases in every 1 million people, hepatic epithelioid hemangioendothelioma (HEHE) is a rare vascular endothelial cell tumor occurring in the liver and consisting of epithelioid and histiocyte-like vascular endothelial cells in mucus or a fibrotic matrix. HEHE is characterized as a low-to-moderate grade malignant tumor and is classified into three types: solitary, multiple, and diffuse. Both the etiology and characteristic clinical manifestations of HEHE are unclear. However, HEHE has a characteristic appearance on imaging including ultrasound, magnetic resonance imaging, and positron emission tomography/computerized tomography. Still, its diagnosis depends mainly on pathological findings, with immunohistochemical detection of endothelial markers cluster of differentiation 31 (CD31), CD34, CD10, vimentin, and factor VIII antigen as the basis of diagnosis. Hepatectomy and/or liver transplantation are the first choice for treatment, but various chemotherapeutic drugs are reportedly effective, providing a promising treatment option. In this review, we summarize the literature related to the diagnosis and treatment of HEHE, which provides future perspectives for the clinical management of HEHE.

[Fluorescence in situ hybridization for the diagnosis of soft-tissue and bone tumors]

Mesenchymal tumors, especially high-grade sarcomas, frequently harbor chaotic genotypes. Few tumors arise in association with genetic tumor predisposition syndromes with germline mutations in tumor suppressor genes. An increasing number of soft-tissue and bone tumors are characterized by recurrent genomic alterations, which can be utilized for diagnostic purposes. These include translocations and amplifications and less frequently deletions. These alterations can be detected by fluorescence in situ hybridization among other techniques. The rising number of whole genome sequencing of soft-tissue and bone tumors leads to an improved understanding of tumor genetics. On this basis, fluorescence in situ hybridization has gained relevance as a diagnostic tool. This review covers relevant genetic alterations in lipomatous tumors, soft-tissue tumors with spindle-cell and epithelioid morphology, vascular tumors, small-blue-round-cell tumors, and bone tumors that are detectable by fluorescence in situ hybridization.

How Technology Is Improving the Multidisciplinary Care of Sarcoma

Sarcomas are rare tumors but comprise a wide histologic spectrum. Advances in technology have emerged to address the biologic complexity and challenging diagnosis and treatment of this disease. The diagnostic approach to sarcomas has historically been based on morphologic features, but technologic advances in immunohistochemistry and cytogenetic/molecular testing have transformed the interdisciplinary work-up of mesenchymal neoplasms in recent years. On the therapeutic side, technologic advances in the delivery of radiation have made it a linchpin in the treatment of localized and oligometastatic sarcoma. In this review, we discuss recent advances in the pathologic diagnosis of sarcomas and discuss select sarcoma types that illustrate how newly discovered diagnostic, prognostic, and predictive biomarkers have refined existing classification schemes and substantially shaped our diagnostic approach. Such examples include conventional and epithelioid malignant peripheral nerve sheath tumors (MPNSTs), emerging entities in the group of round cell sarcomas, and other mesenchymal neoplasms with distinct cytogenetic aberrations. Recent advances in radiation oncology, including intensity-modulated, stereotactic, MRI-guided, and proton radiotherapy (RT), will be reviewed in the context of neoadjuvant or adjuvant localized soft-tissue sarcoma and oligometastatic or oligoprogressive disease. Innovations in translational research are expected to be introduced into clinical practice over the next few years and will likely continue to affect the rapidly evolving field of sarcoma diagnostics and therapy.

Genetic investigation of childhood vascular tumor biology reveals pathways for therapeutic intervention

Vascular tumors are neoplasms of endothelial cells, a significant number of which present in childhood. Recent studies have examined the mutational landscape of many subtypes of vascular tumors, identifying mutations primarily within the Ras–mitogen-activated protein kinase (MAPK) pathway and providing a unique opportunity to consider targeted therapeutics. This review will summarize the current understanding of childhood vascular tumor pathobiology.

The Molecular Diagnostics of Vascular Neoplasms

In this review, we provide an update of the recently discovered, diagnostically significant genetic aberrations harbored by a subset of vascular neoplasms. From benign (epithelioid hemangioma, spindle cell hemangioma), to intermediate (pseudomyogenic hemangioendothelioma), to malignant (epithelioid hemangioendothelioma, angiosarcoma), each neoplasm features a mutation or gene fusion that facilitates its diagnosis by immunohistochemistry and/or molecular ancillary testing. The identification of these genetic anomalies not only assists with the objective classification and diagnosis of these neoplasms, but also serves to help recognize potential therapeutic targets.

Clinical characteristics of epithelioid hemangioendothelioma: a single-center retrospective study

Background

Epithelioid hemangioendothelioma (EHE) is a rare malignant vascular neoplasm with increasing incidence. However, its clinical characteristics remain unclear due to its low incidence. This study aimed to investigate the features of EHE.

Methods

Patients with EHE treated at our institution between January 2000 and June 2018 were enrolled. Data including demographic characteristics, treatment patterns, pathological results, and prognosis were collected, and a retrospective database was constructed for analysis.

Results

The cohort comprised 33 patients with a mean age of 48.0 ± 16.0 years. Eighteen (54.5%) patients were asymptomatic. The laboratory tests were unremarkable except in five and two patients who had increased CA 125 and CA 19-9, respectively. Twenty-one patients underwent surgery, while 12 patients underwent only biopsy. The postoperative morbidity rate was 28.6% (6/21). The anatomical sites of the primary lesions varied. Immunohistochemical staining was positive for CD34 and CD31 in most patients. Twenty-six patients (78.8%) were followed up at a range of 1–201 months, and 6 patients died during this period. The 1-, 3-, and 5-year cumulative survival rates were 96.2%, 87.0%, and 75.3%, respectively. The patients who had metastases or only underwent biopsy showed significantly higher mortality.

Conclusions

EHE is a rare malignant vascular tumor that can occur in any site of the body. Surgery is the primary choice of treatment, and pathologic evaluation is the gold standard for diagnosis. Metastases and unresectability are associated with poor prognosis.

Hepatic Epithelioid Hemangioendothelioma

Epithelioid hemangioendothelioma is a rare vascular tumor, composed of epithelioid and histiocytoid vascular endothelial cells in myxoid or fibrotic stroma, which can arise in multiple locations throughout the body. In the liver, this neoplasm usually presents on imaging as an incidental finding of multifocal, heterogeneously enhancing nodules in both lobes or presents clinically with nonspecific abdominal symptoms. Histologically, the tumor has been mistaken for metastatic carcinoma, angiosarcoma, hepatocellular carcinoma, and cholangiocarcinoma. The neoplasm usually stains positive for vascular markers, such as factor VIII-related antigen, CD31, and CD34, and negative for cytokeratins. The translocation t(1;3)(p36.3;q25), resulting in the CAMTA1- WWTR1 fusion product, is the most commonly identified genetic abnormality with this tumor. Although hepatic epithelioid hemangioendothelioma can have a varied clinical course, it is generally considered less aggressive than angiosarcoma. There is no consensus treatment protocol and techniques including liver transplantation, liver resection, chemotherapy and/or radiation therapy, and surveillance have all been used with varying outcomes.

Limited biopsies of soft tissue tumors: the contemporary role of immunohistochemistry and molecular diagnostics

Diagnosing soft tissue tumors is challenging, even on ample incisional biopsies or resection specimens. There are more than 100 distinct types of soft tissue neoplasms, including more than 80 benign and intermediate mesenchymal tumors and around 40 soft tissue sarcomas. Accurate diagnosis relies first upon recognition of characteristic histologic and cytologic features, including architecture, stromal characteristics, vascular patterns, and dominant cytology; these features may not be represented or apparent in limited core needle biopsy or fine needle aspiration specimens. Once a differential diagnosis is established, application of immunohistochemistry and cytogenetic or molecular diagnostic assays (especially fluorescence in situ hybridization) is used in an attempt to reach a specific diagnosis. In recent years, the diagnostic armamentarium for soft tissue tumors has expanded dramatically, following the discovery of molecular alterations that underlie the pathogenesis of soft tissue tumors. These include new diagnostic immunohistochemical markers that serve as useful surrogates for molecular genetic alterations. Availability of such markers has improved our ability to render accurate and specific diagnoses based on limited biopsy samples. In this review, examples of recently developed markers for the diagnosis of selected soft tissue tumor types will be discussed, including solitary fibrous tumor (STAT6), malignant peripheral nerve sheath tumor (H3K27me3), epithelioid hemangioendothelioma (CAMTA1), dedifferentiated liposarcoma (MDM2), and CIC-DUX4 sarcoma (WT1 and ETV4).

Diagnostic Immunohistochemistry for Soft Tissue and Bone Tumors: An Update

Although some soft tissue and bone tumors can be identified based on histologic features alone, immunohistochemistry plays a critical diagnostic role for most mesenchymal tumor types. The discovery of recurrent genomic alterations in many benign and malignant mesenchymal neoplasms has added important biologic insights and expanded the spectrum of some diagnostic subgroups. Some tumors are defined by unique genomic alterations, whereas others share abnormalities that are not tumor-specific and can be observed in a sometimes broad range of biologically unrelated neoplasms. We herein focus on novel immunohistochemical markers, based on molecular genetic alterations, which are particularly useful in the diagnostic workup of selected groups of soft tissue and bone tumors, including recently described entities, specifically round cell sarcomas (Ewing sarcoma, CIC-rearranged sarcoma, and BCOR-rearranged sarcoma), vascular tumors (epithelioid hemangioma, epithelioid hemangioendothelioma, and pseudomyogenic hemangioendothelioma), SMARCB1-deficient neoplasms, adipocytic tumors (spindle cell/pleomorphic lipoma, atypical spindle cell lipomatous tumor, and conventional atypical lipomatous tumor), giant cell-rich bone tumors (giant cell tumor of bone and chondroblastoma), and biphenotypic sinonasal sarcoma. Given the complex nature of sarcoma classification, and the rarity of many mesenchymal tumor types, careful integration of clinical presentation, imaging features, histology, immunophenotype, and cytogenetic/molecular alterations is crucial for accurate diagnosis of soft tissue and bone tumors.

Epithelioid Hemangioendothelioma as a Model of YAP/TAZ-Driven Cancer: Insights from a Rare Fusion Sarcoma

Epithelioid hemangioendothelioma (EHE) is a rare soft-tissue sarcoma involving cells with histologic markers that suggest an endothelial origin. Around 90% of EHEs are caused by the fusion of Transcriptional Co-activator with a PDZ-motif (TAZ) with Calmodulin Binding Transcription Activator 1 (CAMTA1), a central nervous system-specific transcription activator. The 10% of EHEs that lack the TAZ–CAMTA1 fusion instead have a fusion of Yes-associated Protein (YAP) and Transcription Factor E3 (TFE3) genes (YAP-TFE3). YAP and TAZ are well-defined downstream effectors in the Hippo pathway that promote cell growth when translocated to the nucleus. The TAZ–CAMTA1 fusion transcript is insensitive to the Hippo inhibitory signals that normally prevent this process and thus constitutively activates the TAZ transcriptome. In EHE, this causes tumors to form in a variety of organs and tissue types, most commonly the liver, lung, and bone. Its clinical course is unpredictable and highly variable. TAZ activation is known to contribute to key aspects of the cancer phenotype, including metastasis and fibrosis, and increased expression of TAZ is thought to be causally related to the progression of many cancers, including breast, lung, and liver. Therefore, understanding TAZ biology and the molecular mechanisms by which it promotes unregulated cell proliferation will yield insights and possibly improved treatments for both EHE as well as much more common cancers.

Recent advances in the diagnosis of soft tissue tumours

Soft tissue tumours are relatively rare, but are diagnostically challenging as they comprise a large spectrum of diagnostic entities. Substantial advances have been made in recent years in identifying the underlying recurrent chromosomal and genomic alterations in a significant subset of soft tissue tumours, and this continues to enrich our understanding of the biological mechanisms of tumour development and progression. Ongoing validation and integration of these findings into existing pathological-diagnostic algorithms has led to re- or subclassification of diagnostic categories and will continue to shape a more nuanced (and hopefully clinically relevant) tumour classification system in the future. This review provides a selective overview of recent diagnostic or conceptual advances in the categories of peripheral nerve sheath tumours, vascular and adipocytic tumours, round cell and myogenic sarcomas, and gastrointestinal stromal tumours, as well as their underlying molecular mechanisms, some of which have been translated successfully into useful immunohistochemical stains. A thorough and critical validation of newly identified diagnostic markers-acknowledging the fact that some genetic alterations may not necessarily be tumour-specific-and ongoing correlation with clinical and prognostic implications will be necessary in this regard.

New Insights about Pulmonary Epithelioid Hemangioendothelioma: Review of the Literature and Two Case Reports

Pulmonary epithelioid hemangioendothelioma (PEH) is a rare neoplasm of vascular origin. There are three different major imaging patterns identified in thoracic manifestation of epithelioid hemangioendothelioma: (1) multiple pulmonary nodules; (2) multiple pulmonary reticulonodular opacities; and (3) diffuse infiltrative pleural thickening. Radiographically, presence of bilateral multiple nodules is the most common pattern of presentation. The diagnosis is made on the basis of histopathological findings and confirmed by positive immunohistochemistry staining. Although the prognostic factors for PEH have not yet been well established, a better prognosis is usually associated with the multinodular pattern. We report two different imagological presentations of this rare disease, based on two institutional experiences, along with a review of the relevant literature.

Refractory Kaposiform Hemangioendothelioma Associated with the Chromosomal Translocation t(13;16)(q14;p13.3)

We report a 7-year-old male with a history of recurrent kaposiform hemangioendothelioma (KHE) in the sacral area and multiple thoracic vertebral lesions. Tumor karyotyping revealed the balanced translocation t(13;16)(q14;p13.3). He had mildly decreased platelet counts but never experienced any episodes of Kasabach-Merritt phenomenon. He was treated with vincristine for 1 year but improvement was minor. Significant clinical improvement was seen with sirolimus therapy. To the best of our knowledge, this is the first report to demonstrate that KHE is associated with a clonal karyotypic abnormality.

TFE3-rearranged hepatic epithelioid hemangioendothelioma-a case report with immunohistochemical and molecular study

A recurrent YAP1-TFE3 gene fusion has been identified in WWTR1-CAMTA1-negative epithelioid hemangioendotheliomas arising in soft tissue, bone, and lung, but not in liver. We present the first case of TFE3-rearranged hepatic epithelioid hemangioendothelioma in a 39-year-old Taiwanese woman. Computed tomography scan revealed multifocal, ill-defined nodules involving both hepatic lobes. She then underwent deceased donor liver transplantation. Histologically, the tumors in the liver explant showed a biphasic growth pattern. One component was composed of dilated and well-formed blood vessels lined by epithelioid cells with abundant eosinophilic cytoplasm, mimicking an alveolar pattern, whereas the other component was composed of cords and single cells, featuring intracytoplasmic vacuoles, separated by a myxoid stroma. The tumor cells showed vesicular nuclei and small indistinct nucleoli with mild to moderate cytologic atypia. Most tumor cells showed factor VIII, CD34, CD31, and TFE3 positivity in immunohistochemical study. Fluorescence in situ hybridization analysis for the tumor cells exhibited TFE3 gene rearrangement. The patient is currently alive, and no post-operative tumor recurrence developed during a 13-year follow-up. Awareness of this rare vasoformative variant and identification of the gene rearrangement would be helpful on differential diagnosis with other high-grade carcinoma and angiosarcoma of liver.

Advances in the Genetic Characterization of Cutaneous Mesenchymal Neoplasms: Implications for Tumor Classification and Novel Diagnostic Markers

Cutaneous mesenchymal neoplasms often pose significant diagnostic challenges; many such entities are rare or show clinical and histologic overlap with both other mesenchymal and non-mesenchymal lesions. Recent advances in the genetic classification of many cutaneous mesenchymal neoplasms have not only helped define unique pathologic entities and increase our understanding of their biology, but have also provided new diagnostic markers. This review details these recent discoveries, with a focus on their implications for tumor classification and diagnosis.

The clinical features of epithelioid hemangioendothelioma in a Han Chinese population: A retrospective analysis

Epithelioid hemangioendothelioma (EHE) is a rare indolent vascular tumor which occurs at liver, lung, bone, and so on. However, the etiology of EHE is evasive.These patients were enrolled at the First Affiliated Hospital of Xi'an Jiaotong University from January 2011 to December 2015. Retrospective analysis is done by demographic data of clinical manifestations, laboratory parameters, CT imaging, histological, and immunohistochemical features in 9 cases in Shaanxi.Of the patients, 8 were females (88.9%) and 1 were males (11.1%). The age ranged from 34 to 71 years (mean 49 years; median 49 years). Anatomical sites of primary lesions were as follows: liver (n = 6, 66.7%), upper extremities (n = 1, 11.1%), sublingual gland (n = 1, 11.1%), and spine (n = 1, 11.1%). Metastatic disease was diagnosed in 5 cases (55.6%) with occurrence in lung (n = 4, 44.4%), bone (n = 2, 22.2%), upper extremities (n = 1, 11.1%), pleura (n = 1, 11.1%), and spleen (n = 1, 11.1%). Tumor size ranged from 0.5 to 6.8 cm (mean 3 cm). The most tumors were composed of highly cellular areas with small and prominent nucleoli in vesicular nuclei, and ERG (100%) was the most frequently positive in these cases, followed by CD31 (88.9%) and CD34 (77.8%) via histology and immunohistochemistry techniques.EHE is a very rare in Shaanxi. It is significant to find its clinical, radiological, and pathological characters, helping for EHE early diagnosis and treatment, reducing misdiagnosis and improving life quality.

Relevance of Fusion Genes in Pediatric Cancers: Toward Precision Medicine

Pediatric cancers differ from adult tumors, especially by their very low mutational rate. Therefore, their etiology could be explained in part by other oncogenic mechanisms such as chromosomal rearrangements, supporting the possible implication of fusion genes in the development of pediatric cancers. Fusion genes result from chromosomal rearrangements leading to the juxtaposition of two genes. Consequently, an abnormal activation of one or both genes is observed. The detection of fusion genes has generated great interest in basic cancer research and in the clinical setting, since these genes can lead to better comprehension of the biological mechanisms of tumorigenesis and they can also be used as therapeutic targets and diagnostic or prognostic biomarkers. In this review, we discuss the molecular mechanisms of fusion genes and their particularities in pediatric cancers, as well as their relevance in murine models and in the clinical setting. We also point out the difficulties encountered in the discovery of fusion genes. Finally, we discuss future perspectives and priorities for finding new innovative therapies in childhood cancer.

Epithelioid hemangioendotheliomas with TFE3 gene translocations are compossible with CAMTA1 gene rearrangements

Epithelioid hemangioendotheliomas (EHEs) are vascular tumors of intermediate malignancy that can undergo high-grade malignant transformations. EHEs have been characterized by tumor-specific WW domain-containing transcription regulator 1(WWTR1)-calmodulin-binding transcription activator 1 (CAMTA1) translocations, and recently, a novel Yes-associated protein 1 (YAP1)-transcription factor E3 (TFE3) gene fusion was identified in EHEs. In this study, we examined the expression levels of TFE3 and CAMTA1 via immunohistochemical staining and identified chromosomal alterations using fluorescence in situ hybridization (FISH) assays and RT-PCR tests. Although all of the EHEs were CAMTA1-positive in immunohistochemical staining, only five out of 18 EHEs (27.78%) positively expressed nuclear TFE3. The five TFE3-positive EHEs exhibited TFE3 gene break-apart in FISH assays. YAP1-TFE3 gene fusions were confirmed by RT-PCR. Interestingly, we observed CAMTA1 gene break-apart in all of the five TFE3-positive EHEs via FISH assays, and four out of the five TFE3-positive EHEs exhibited WWTR1-CAMTA1 gene fusions via RT-PCR. These results indicate that these two chromosomal alterations are not mutually exclusive but compossible in EHEs. Finally, primary tumor sites in TFE3-positive EHEs consistently contained single masses (P = 0.0359) with larger sizes (P = 0.0550) compared to TFE3-negative EHEs. Similar to previous reports, we observed well-formed vessels more frequently in TFE3-positive EHEs than in TFE3-negative EHEs (P = 0.0441). In addition, TFE3-positive EHEs tended to more frequently demonstrate high-grade nuclear atypia (P = 0.0654) and hypercellularity (P=0.0987) than TFE3-negative EHEs. Thus, we have now established two clinically distinct subgroups of EHEs: TFE3-positive and TFE3-negative EHEs.

The 2015 World Health Organization Classification of Lung Tumors: Impact of Genetic, Clinical and Radiologic Advances Since the 2004 Classification

The 2015 World Health Organization (WHO) Classification of Tumors of the Lung, Pleura, Thymus and Heart has just been published with numerous important changes from the 2004 WHO classification. The most significant changes in this edition involve (1) use of immunohistochemistry throughout the classification, (2) a new emphasis on genetic studies, in particular, integration of molecular testing to help personalize treatment strategies for advanced lung cancer patients, (3) a new classification for small biopsies and cytology similar to that proposed in the 2011 Association for the Study of Lung Cancer/American Thoracic Society/European Respiratory Society classification, (4) a completely different approach to lung adenocarcinoma as proposed by the 2011 Association for the Study of Lung Cancer/American Thoracic Society/European Respiratory Society classification, (5) restricting the diagnosis of large cell carcinoma only to resected tumors that lack any clear morphologic or immunohistochemical differentiation with reclassification of the remaining former large cell carcinoma subtypes into different categories, (6) reclassifying squamous cell carcinomas into keratinizing, nonkeratinizing, and basaloid subtypes with the nonkeratinizing tumors requiring immunohistochemistry proof of squamous differentiation, (7) grouping of neuroendocrine tumors together in one category, (8) adding NUT carcinoma, (9) changing the term sclerosing hemangioma to sclerosing pneumocytoma, (10) changing the name hamartoma to "pulmonary hamartoma," (11) creating a group of PEComatous tumors that include (a) lymphangioleiomyomatosis, (b) PEComa, benign (with clear cell tumor as a variant) and

Epithelioid Hemangioendothelioma: a Rare Primary Thyroid Tumor with Confirmation of WWTR1 and CAMTA1 Rearrangements

We report a rare case of epithelioid hemangioendothelioma as a primary thyroid tumor. To our knowledge, there are only two prior unequivocal cases of primary thyroid epithelioid hemangioendothelioma reported in the English literature. This is the first case in the thyroid with molecular confirmation.

Advances in the clinicopathological and molecular classification of cutaneous mesenchymal neoplasms

In recent years, there have been several important refinements in the classification of cutaneous mesenchymal neoplasms, including the description of new tumour types, along with the identification of novel and recurrent molecular genetic findings. In addition to providing new insights into tumour biology, many of these advances have had significant clinical consequences with regard to diagnostics, management, and prognostication. Newly described entities include pseudomyogenic haemangioendothelioma, haemosiderotic fibrolipomatous tumour, and fibroblastic connective tissue naevus, which are reviewed in the context of the principal differential diagnoses and significant clinical implications. Genetic characterization of several soft tissue tumour types that occur in the skin has resulted in the identification of diagnostically useful markers: ALK gene rearrangement with corresponding ALK protein expression by immunohistochemistry in epithelioid fibrous histiocytoma; the WWTR1-CAMTA1 fusion gene with CAMTA1 protein expression in epithelioid haemangioendothelioma; MYC amplification and overexpression in radiation-associated angiosarcoma; and EWSR1 gene rearrangement in cutaneous myoepithelial tumours. Finally, the classification of intradermal smooth muscle tumours and unclassified/pleomorphic dermal sarcoma has been refined, resulting in both improved classification and improved prognostication. Many of the tumour types listed above are encountered not only by specialist dermatopathologists, but also by practising general surgical pathologists, and this review should therefore provide a widely applicable update on the histological and molecular classification of cutaneous mesenchymal neoplasms, along with the appropriate use of ancillary diagnostic tests, in particular immunohistochemistry, in the evaluation of such lesions and their histological mimics.