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.

NR1D1::MAML1 epithelioid and spindle cell sarcoma mimicking pseudomyogenic hemangioendothelioma in core biopsy: A case report and review of the literature.

Epithelioid and spindle cell sarcomas with NR1D1::MAML1/2 gene fusions are rare and emerging entities. Only six cases of NR1D1-rearranged mesenchymal tumors have previously been reported in the literature; they are often characterized by an epithelioid morphology, at least focal pseudogland formation, prominent cytoplasmic vacuoles, and focal to diffuse immunohistochemical expression of keratin. We herein report the first case of an NR1D1::MAML1 epithelioid and spindle cell sarcoma with dual immunohistochemical expression of ERG and FOSB, mimicking a pseudomyogenic hemangioendothelioma (PHE) on core biopsy. The sarcoma arose in the left forearm of a 64-year-old man. Initial biopsy showed a mesenchymal neoplasm composed of epithelioid and spindle cells dispersed in myxoid stroma with scattered stromal neutrophils. The morphologic features, combined with the dual immunohistochemical expression of ERG and FOSB, initially mimicked PHE, representing an important potential diagnostic pitfall. The patient subsequently underwent a radical resection, which showed a much more diffuse epithelioid appearance with nested architecture and pseudogland formation. Next-generation sequencing was performed on the resection specimen, which revealed an NR1D1::MAML1 gene fusion, confirming the final diagnosis. Given the fully malignant potential of this tumor, knowledge and recognition of this rare entity are essential to ensure proper management, prevent misdiagnosis, and further characterize the clinical course of this emerging entity. Comprehensive molecular testing can help to identify these rare tumors and exclude the possibility of epithelioid mimics, including PHE.

Cellular variant of kaposiform lymphangiomatosis: a report of three cases, expanding the morphologic and molecular genetic spectrum of this rare entity.

Kaposiform lymphangiomatosis (KLA) is a very rare form of generalized lymphatic anomaly, consisting of a diffuse proliferation of abnormal, dilated lymphatics, and small fascicles of hemosiderin-laden spindled lymphatic endothelial cells. KLA occurs in children and young adults and may present with multicentric disease, pleural and pericardial effusions, and life-threatening coagulopathy. Genetically, KLA most often harbors somatic activating mutations in NRAS. We recently encountered 3 cases of KLA with cellular features, resembling kaposiform hemangioendothelioma (KHE), and studied their clinicopathologic, radiologic, and molecular genetic features. The patients (1 male, 2 females; aged 2 years, 2 months, 4 years) presented with multicentric disease involving skin, soft tissue, bone, and spleen and thrombocytopenia/coagulopathy. Advanced imaging studies confirmed multicentric disease. Biopsies (skin, soft tissue, bone, and spleen) demonstrated both conventional KLA and much more cellular foci, consisting of sheets, nodules, glomeruloid structures, and sieve-like arrays of lymphatic endothelial cells (positive for CD31 and D2-40). Cellular areas superficially resembled KHE but displayed more epithelioid cytology and lacked surrounding hyaline fibrosis and minute platelet aggregates. Molecular genetic studies demonstrated NRAS c.181C > A p.Q61K (Gln61Lys) in 2 specimens from one patient and HRAS p.A59_Q61delinsGGSIL in another. Two patients were treated with sirolimus; all are currently alive with stable disease. We conclude that cellular morphology in KLA, a previously undescribed feature, does not appear to be associated with clinical features, site of disease, mutation type, response to sirolimus, or outcome. Although cellular KLA may mimic KHE, there are sufficient clinical, morphologic, and genetic differences such that these are likely unrelated diseases.

Recent advances in the diagnosis, classification and molecular pathogenesis of cutaneous mesenchymal neoplasms.

The diagnosis of cutaneous mesenchymal neoplasms remains challenging, due to a combination of overlapping histological features, the rarity of some diagnoses and often inadequate sampling in superficial biopsies. Here, we describe recent advances in cutaneous mesenchymal neoplasms. We discuss improvements in our understanding of the molecular pathogenesis of non-neural granular cell tumour, epithelioid fibrous histiocytoma, composite and retiform haemangioendothelioma and dermatofibrosarcoma protuberans. We also discuss recently described tumour types, including some discovered via molecular testing: EWSR1::SMAD3-rearranged fibroblastic tumour, clear cell neoplasm with MITF::CREM rearrangement and melanocytoma with CRCT1::TRIM11 rearrangement, and some discovered via traditional histopathology: superficial CD34-positive fibroblastic tumour, plexiform myofibroblastoma and clear cell neoplasm with melanocytic differentiation and ACTIN::MITF translocation.

The genetics of vascular tumours: an update.

Recent molecular advances have shed significant light on the classification of vascular tumours. Except for haemangiomas, vascular lesions remain difficult to diagnose, owing to their rarity and overlapping clinical, radiographic and histological features across malignancies. In particular, challenges still remain in the differential diagnosis of epithelioid vascular tumours, including epithelioid haemangioma and epithelioid haemangioendothelioma at the benign/low-grade end of the spectrum, and epithelioid angiosarcoma at the high-grade end. Historically, the classification of vascular tumours has been heavily dependent on the clinical setting and histological features, as traditional immunohistochemical markers across the group have often been non-discriminatory. The increased application of next-generation sequencing in clinical practice, in particular targeted RNA sequencing (such as Archer, Illumina), has led to numerous novel discoveries, mainly recurrent gene fusions (e.g. those involving FOS, FOSB, YAP1, and WWTR1), which have resulted in refined tumour classification and improved diagnostic reproducibility for vascular tumours. However, other molecular alterations besides fusions have been discovered in vascular tumours, including somatic mutations (e.g. involving GNA family and IDH genes) in a variety of haemangiomas, as well as copy number alterations in high-grade angiosarcomas (e.g. MYC amplifications). Moreover, the translation of these novel molecular abnormalities into diagnostic ancillary markers, either fluorescence in-situ hybridisation probes or surrogate immunohistochemical markers (FOSB, CAMTA1, YAP1, and MYC), has been remarkable. This review will focus on the latest molecular discoveries covering both benign and malignant vascular tumours, and will provide practical diagnostic algorithms, highlighting frequently encountered pitfalls and challenges in the diagnosis of vascular lesions.

Recurrent PTBP1::MAML2 fusions in composite hemangioendothelioma with neuroendocrine differentiation: A report of two cases involving neck lymph nodes.

Composite hemangioendothelioma (CHE) displaying neuroendocrine differentiation is a rare histologic variant that is often mistaken for angiosarcoma, having a predilection for visceral locations and being associated with an aggressive clinical course. Their pathogenesis is still evolving, with only two cases to date from separate studies reporting a recurrent PTBP1-MAML2 fusion. Herein, we report two new cases of neuroendocrine CHE harboring PTBP1-MAML2 fusions occurring in two elderly patients (70-year-old male and 71-year-old female), both involving neck lymph nodes. The first case presented with multifocal cervical lymphadenopathy, while the second case occurred unifocally in an enlarged neck lymph node. Histologically, the tumors displayed heterogenous architectural patterns with areas reminiscent of benign cavernous hemangioma, retiform hemangioendothelioma, epithelioid hemangioendothelioma, and angiosarcoma. Cytologically, the cells were monotonous with round to ovoid nuclei, open to fine chromatin, scant to moderate cytoplasm, and frequent vacuolization. In addition, the first case showed focal solid areas of large epithelioid cells with severe nuclear atypia, enlarged nuclei and prominent nucleoli, resembling epithelioid angiosarcoma. Tumor cells were diffusely positive for vascular markers and focally positive for synaptophysin. In both cases, a next-generation sequencing fusion panel confirmed an in-frame fusion between PTBP1 exon 10 and MAML2 exon 2. One case with clinical follow-up showed stable recurrent disease and metastatic lung deposits following treatment. Both patients were alive at 3 months and 1 year following initial diagnosis. Our findings lend further support to classifying CHE with PTBP1-MAML2 fusions as a distinct variant of CHE with unique clinicopathologic features, including neuroendocrine features.

A novel SERPINE1-FOSB fusion gene in pseudomyogenic hemangioendothelioma results in activation of intact FOSB and the PI3K-AKT-mTOR signaling pathway and responsiveness to sirolimus.

Pseudomyogenic hemangioendothelioma (PHE) is an extremely rare disease that affects mainly the young and more men than women. PHE are multicentric, locally aggressive, have low metastatic potential, and affect multiple tissue planes. Genetic aberrations are frequently detected in PHE and may play important roles in the occurrence, development, and treatment of this disease. In this study, we report a case of PHE with a novel SERPINE1-FOSB fusion gene. The fusion introduced a strong promoter near the coding region of FOSB, resulting in overexpression of intact FOSB. Immunohistochemical analysis showed overexpression of pAKT and mTOR in tumor cells, suggesting activation of the PI3K-AKT-mTOR signaling pathway. The patient responded well to targeted therapy with sirolimus, an mTOR inhibitor. Our study correlated dysregulation of a specific signaling pathway and the effectiveness of a targeted therapy to a specific genetic aberration. This information may be useful for future investigations of targeted therapeutics and provide a potential predictive biomarker for therapeutic effectiveness in PHE cases.

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.

Kaposiform hemangioendothelioma further broadens the phenotype of PIK3CA-related overgrowth spectrum.

Kaposiform hemangioendothelioma (KHE) is a rare locally aggressive mixed vascular tumor, with typical onset in early childhood and characterized by progressive angio- and lymphangiogenesis. Its etiopathogenesis and molecular bases are still unclear. Here, we report the first case of congenital KHE harboring a PIK3CA mosaic pathogenic variant (c.323G > A, p.Arg108His) in a boy with very subtle PIK3CA-related overgrowth spectrum (PROS) features. This finding provides insights into the pathophysiology of KHE, offering targeted therapeutic options by inhibition of the PI3K/Akt/mTOR pathway. We propose the inclusion of this mixed lymphatic and vascular anomaly within the PROS.

A novel CLTC-FOSB gene fusion in pseudomyogenic hemangioendothelioma of bone.

Pseudomyogenic hemangioendothelioma, an uncommon mesenchymal neoplasm composed of plump spindled and/or epithelioid endothelial cells, may present multicentrically and tends to locally recur but rarely metastasizes. Morphologic resemblance to epithelioid sarcoma and other spindle cell neoplasms may result in diagnostic confusion. Molecular characterization of pseudomyogenic hemangioendothelioma has revealed these neoplasms often harbor a rearrangement of the FOSB gene with SERPINE1 or ACTB as recurrent fusion gene partners. Herein, a case of a fibular pseudomyogenic hemangioendothelioma with minimal extension into the adjacent soft tissue arising in a 17 year-old male is presented. The neoplasm exhibited sheets of epithelioid cells with abundant eosinophilic cytoplasm and variably eccentric nuclei. RNA sequencing revealed a novel CLTC-FOSB fusion transcript that was subsequently confirmed by direct sequencing of reverse transcription-polymerase chain reaction products demonstrating an in-frame fusion between exon 17 of the clathrin heavy chain (CLTC) gene and exon 2 of the FOSB (FosB proto-oncogene, AP-1 transcription factor subunit) gene. CLTC-FOSB fusion has not been described in a neoplasm before.

Recurrent YAP1 and MAML2 Gene Rearrangements in Retiform and Composite Hemangioendothelioma.

Retiform and composite hemangioendotheliomas (CHEs) are both locally aggressive, rarely metastasizing vascular neoplasms characterized by arborizing vascular channels lined by endothelial cells with a hobnail morphology. CHE displays additional cytologic and architectural components, including often vacuolated epithelioid cells, solid areas, or features reminiscent of well-differentiated angiosarcoma. Triggered by an index case of a soft tissue retiform hemangioendothelioma (RHE) which revealed a YAP1-MAML2 gene fusion by targeted RNA sequencing, we sought to investigate additional cases in this morphologic spectrum for this genetic abnormality. A total of 24 cases, 13 RHE and 11 CHE involving skin and soft tissue were tested by fluorescence in situ hybridization using custom BAC probes for rearrangements involving these genes. An additional visceral CHE with neuroendocrine differentiation was tested by targeted RNA sequencing. Among the soft tissue cohort, 5/13 (38%) RHE and 3/11 (27%) CHE showed YAP1 gene rearrangements, with 5 cases showing a YAP1-MAML2 fusion, including all 3 CHE. The single neuroendocrine CHE showed the presence of a PTBP1-MAML2 fusion. All YAP1-positive CHE lesions occurred in female children at acral sites, compared with fusion-negative cases which occurred in adults, with a wide anatomic distribution. YAP1-positive RHE occurred preferentially in males and lower limb, compared with negative cases. These results suggest that RHE and CHE represent a morphologic continuum, sharing abnormalities in YAP1 and MAML2 genes. In contrast, the neuroendocrine CHE occurring in a 37-year-old male harbored a distinct PTBP1-MAML2 fusion and showed aggressive clinical behavior (pancreatic mass with multiple liver and lung metastases). These preliminary findings raise the possibility that neuroendocrine CHE may be genetically distinct from the conventional RHE/CHE spectrum. Further studies are needed to investigate the pathogenetic relationship of fusion-negative cases with this subset and, less likely, with other members of the HE family of tumors.

Molecular characterization of hepatic epithelioid hemangioendothelioma reveals alterations in various genes involved in DNA repair, epigenetic regulation, signaling pathways, and cell cycle control.

Epithelioid hemangioendotheliomas (EHE) of the liver are rare, low-malignant vascular tumors whose molecular pathogenesis is incompletely understood. The diagnosis of EHE is challenging, and the course of the disease can be highly variable. Therapeutic options for EHE are limited, including resection of primary and metastatic tumors, organ transplantation and rather ineffective systemic approaches. Driver mutations have been reported (fusion transcripts of either YAP-TFE3 or WWTR1-CAMTA1) but comprehensive molecular profiling has not been performed. Our aim was to molecularly characterize hepatic EHE to identify new molecular targets. Eight primary hepatic EHE were analyzed by next-generation sequencing using a 409-gene panel. The majority of primary hepatic EHE revealed a low number of mutations. Genes that were mutated primarily are involved in DNA repair, epigenetic regulation, signaling pathways and cell cycle control, indicating that EHE present with mutations in various functions. Although only detecting a low mutation rate, a comparison with comprehensive databases (target db V3) revealed mutations in five genes with putative therapeutical options. Therefore, our findings help to shed light on the molecular background of EHE and might pave the way to new therapeutic approaches.

What is new in endothelial neoplasia?

The classification of vascular neoplasms continues to evolve as we accumulate more genetic and clinical data, particularly for rare tumor types. Because of tumor rarity, changes to classification schema, overlapping histologic features, and in some cases, lack of morphologic evidence of vasoformation, vascular neoplasms present a diagnostic challenge. Here, we discuss recent developments in our understanding of vascular tumors, with a detailed discussion of epithelioid hemangioma, tufted angioma, kaposiform hemangioendothelioma, composite hemangioendothelioma, pseudomyogenic hemangioendothelioma, epithelioid hemangioendothelioma, and angiosarcoma.

Kaposiform hemangioendothelioma and tufted angioma - (epi)genetic analysis including genome-wide methylation profiling.

Kaposiform hemangioendothelioma (KHE) is a locally aggressive vascular condition of childhood and is clinicopathologically related to tufted angioma (TA), a benign skin lesion. Due to their rarity molecular data are scarce. We investigated 7 KHE and 3 TA by comprehensive mutational analysis and genome-wide methylation profiling and compared the clustering, also with vascular malformations. Lesions were from 7 females and 3 males. The age range was 2 months to 9 years with a median of 10 months. KHEs arose in the soft tissue of the thigh (n = 2), retroperitoneum (n = 1), thoracal/abdominal (n = 1), supraclavicular (n = 1) and neck (n = 1). One patient presented with multiple lesions without further information. Two patients developed a Kasabach-Merritt phenomenon. TAs originated in the skin of the shoulder (n = 2) and nose/forehead (n = 1). Of the 5 KHEs and 2 TAs investigated by DNA sequencing, one TA showed a hot spot mutation in NRAS, and one KHE a mutation in RAD50. Unsupervised hierarchical clustering analysis indicated a common methylation pattern of KHEs and TAs, which separated from the homogeneous methylation pattern of vascular malformations. In conclusion, methylation profiling provides further evidence for KHEs and TAs potentially forming a spectrum of one entity. Using next generation sequencing, heterogeneous mutations were found in a subset of cases (2/7) without the presence of GNA14 mutations, previously reported in KHE and TA.

Fusion of the Genes WWTR1 and FOSB in Pseudomyogenic Hemangioendothelioma.

BACKGROUND/AIM: Pseudomyogenic hemangioendothelioma is a rare endothelial tumor. Previous genetic investigations have shown that the tumors carry either a SERPINE1-FOSB or an ACTB-FOSB fusion gene. The aim of the study was to identify FOSB fusions linked with pseudomyogenic hemangioendothelioma. MATERIALS AND METHODS: RNA sequencing, reverse transcription polymerase chain reaction (RT-PCR) and Sanger sequencing analyses were performed on a pseudomyogenic hemangioendothelioma. RESULTS: An in-frame fusion was found between exon 4 of WWTR1 from 3q25 and exon 2 of FOSB from 19q13. The fusion gene not only places FOSB under the control of the WWTR1 promoter, but is predicted to encode a chimeric WWTR1-FOSB transcription factor. CONCLUSION: FOSB may be fused with SERPINE1, ACTB, or WWTR1 in pseudomyogenic hemangioendotheliomas. The resulting overexpression of FOSB fusion is a potentially useful marker that could be helpful in the diagnosis of these tumors.

Activation of Hedgehog Signaling in Aggressive Hepatic Hemangioma in Newborns and Infants.

BACKGROUND/AIM: Hepatic hemangiomas (HH) can show an aggressive course with significant complications. Prognostic markers that identify an aggressive course are entirely absent. Since we have showed that Hedgehog signaling is overexpressed in aggressive hemangiomas of the skin. Here, we hypothesize that it is also altered in aggressive HH. MATERIALS AND METHODS: Immunohistological staining for GLUT1 and quantitative PCR was performed in seven specimens with aggressive HH. For comparison, we included specimens of kaposiform hemangioendothelioma (KHE), skin hemangioma and normal liver tissue. RESULTS: Overexpression of the Hedgehog signaling components SHH and GLI2 and its target gene FOXA2 in HH were similar to those found in aggressive skin hemangioma and KHE, their expression being significantly higher than in mild skin hemangioma. High expression levels of SHH and FOXA2 positively correlated with HH, but not with normal liver tissue. CONCLUSION: Hedgehog signaling is up-regulated in aggressive HH. This finding may lead to a biomarker allowing early intervention.