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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.

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.

Objectives Pseudomyogenic hemangioendothelioma (PHE) is a rare intermediate hemangioendothelioma. This article aims to study the clinicopathological features of PHE. Methods We collected the clinicopathological features of 10 new PHE, and examined their molecular pathological features by fluorescence in situ hybridization. In addition, we summarized and analyzed the pathological data of 189 reported cases. Results The case group consisted of six men and four women aged 12–83 years (median: 41 years). Five instances occurred in the limbs, three in the head and neck, and two in the trunk. Tumor tissues were composed of spindle cells and round or polygonal epithelioid cells, which were either arranged in sheets or interwoven, along with areas of transitional morphology. Scattered or patchy stromal neutrophil infiltration was observed. Tumor cells had abundant cytoplasm, and some contained vacuoles. The nuclei had mild to moderate atypia, with visible nucleoli, and mitosis was rare. PHE tissues diffusely expressed CD31 and ERG, but not CD34, Desmin, SOX-10, HHV8 or S100, while some samples expressed CKpan, FLI-1 and EMA. INI-1 stain is retained. The proliferation index of Ki-67 is 10–35%. Seven samples were detected by fluorescence in situ hybridization, six of which had breakages in FosB proto-oncogene (AP-1 transcription factor subunit). Two patients experienced recurrence; however, no metastasis or death occurred. Conclusions PHE is a rare soft tissue vascular tumor, which has biologically borderline malignant potential, local recurrence, little metastasis, and good overall survival and prognosis. Immunomarkers and molecular detection are valuable for diagnosis.

Background Malignant hemangioendothelioma is an endothelial cancer with heterogeneous clinical behavior that can range from indolent to aggressive, of which the majority are epithelioid (EHE). Its incidence and demographics have not been previously well defined in a large cohort. Methods This retrospective analysis used the US Cancer Statistics National Program of Cancer Registries – Surveillance Epidemiology End Results (SEER) combined database to identify patients in the US newly diagnosed with hemangioendothelioma between the years of 2001 and 2017 (n = 1986). Survival analyses were performed on a subset of patients within the SEER‐18 database with survival information available (n = 417). Outcomes included incidence, demographics of patients newly diagnosed with hemangioendothelioma, extent of disease at presentation, and overall survival. Results The incidence of hemangioendothelioma in the US is 0.4 cases per million person‐years. Although cases rose to 122 newly diagnosed in the year 2017 (90 EHE, 32 other hemangioendothelioma), incidence rates were stable. Skin and connective tissues were the most common presenting sites (33.4%), followed by liver (24.5%), lung (17.6%), and bone (12.5%). Median age at diagnosis was 55 years; 27.2% of patients were pediatric, adolescent, or young adult (<40 years). At presentation, 36.4% of patients had localized disease; 21.6% presented with regional and 41.7% with distant metastases. Observed survival at 3 years was 79.7%, 70.7%, and 46.0% for patients presenting with local, regional, and distant disease and most deaths occurred within the first 2 years. Conclusions Malignant hemangioendothelioma is ultra‐rare but meaningfully impacts affected patients. These data may provide benchmarks for comparison of new approaches to hemangioendothelioma therapy and highlight poor survival outcomes. Hemangioendothelioma is ultra‐rare with incidence of 0.4 cases per million person‐years but meaningfully impacts affected patients. These data may provide benchmarks for comparison of new approaches to hemangioendothelioma therapy and highlight poor survival outcomes.

We present here our experience with 24 cases of pseudomyogenic hemangioendothelioma (PMHE) to further delineate its clinicopathological spectrum. There were 18 males and 6 females with a median age of 28 years (range 10~64 years). Most patients presented with erythematous nodules or papules, with or without pain. The majority (63%) occurred in the lower extremities, whereas a minority involved the trunk (25%), upper extremities (8%), and head and neck (4%). Six cases (25%) had a primary bone origin. With physical and radiological examinations, 16 cases (67%) manifested as multifocal disease, involving multiple tissue planes or different bones within the anatomic region. Six cases (25%) involved skin, soft tissue, and bone simultaneously. Histologically, all cases showed features consistent with a PMHE characterized by loose fascicles or sheets of plump spindled to epithelioid cells harboring brightly eosinophilic cytoplasm and vesicular nuclei. In addition, five cases (21%) contained a prominent myxoid matrix, and one case displayed perineural and intravascular invasion. The follow-up information available in 18 patients revealed local recurrence in 4 patients (22%) and persistent disease in 8 patients (44%), respectively. One patient developed bilateral pulmonary metastases which showed significant remission after systemic chemotherapy. None of the patients died of the disease. As the clinical appearance of PMHE can be deceptive, a radiological examination is essential in identifying an insidious multifocal disease. Although PMHE has a predilection for the distal extremities of young males, this rare tumor type could also occur in unusual sites and affect middle-aged adults of both genders. The striking myoid appearance in association with myxoid stromal change may represent a potential diagnostic pitfall. Biologically, PMHE has an indolent clinical behavior, albeit metastatic disease may occur in rare instance.

Pseudomyogenic hemangioendothelioma (PMH) is a rare tumor of vascular origin with intermediate malignant potential which commonly presents as a subcutaneous and soft-tissue mass with or without concurrent bone involvement. However, PMH presenting as primary multifocal bone lesions is rare. Histomorphologically, it mimicks other epithelioid tumors and cytokeratin expression in PMH can prompt an erroneous diagnosis of metastatic carcinoma, especially in an elderly patient. Diligent histopathological examination and judicious immunohistochemistry panel can guide to the correct diagnosis. Due to its rarity, the optimal therapeutic strategy has not been established till date. We present a rare case of PMH of primary bone with multifocal bony disease in a 23-year-old male who presented with severe bone pains. The patient has been managed with four weekly denosumab, and the disease is stable with symptomatic relief after 6 months.

ABSTRACT Kaposiform haemangioendothelioma (KHE) research faces challenges due to the lack of established cell lines and suitable animal models. Our study aimed to establish KHE cell lines, spheroids and refine murine models to mimic disease characteristics, advancing our understanding of KHE pathogenesis and exploring novel therapies. Primary KHE cells were sorted using CD31 antibodies and cultured into spheroids. These cells were then injected into mice, and the resulting tumours were analysed using immunohistochemistry. Preliminary exploration of the potential mechanisms of sirolimus action on KHE was conducted through transcriptome sequencing. CD31+ KHE cells were isolated and characterised from three out of six patients. The CD31+ KHE cells demonstrated positive expression of essential markers such as CD31, Ki67 and LYVE1, consistent with the profiles observed in KHE tumours. Additionally, subcutaneous tumours displayed similar positive expression of key markers, reminiscent of KHE tumours. Transcriptome sequencing revealed downregulation of ATG9B after sirolimus treatment in CD31+ KHE cells. CD31+ KHE cells can replicate human KHE in murine models, offering a valuable tool for studying pathogenesis. Our findings also suggest a potential mechanism of sirolimus action in treating KHE, warranting further investigation into novel therapeutic strategies.

Pseudomyogenic hemangioendothelioma (PHE) is a rare, usually multifocal neoplasm typically affecting individuals in the second-to-fourth decade of life, with a male predominance. It often arises in the distal extremities and characteristically involves multiple tissue planes. Presentation of this neoplasm as a primary penile lesion is exceedingly rare, with only five cases previously documented in the literature. We report the clinicopathologic features of five additional PHEs presenting as primary penile tumors and review previously published cases. Tumors affected young to middle-aged adult patients and had a relatively bland clinical appearance, mimicking indolent lesions such as epidermal inclusion cysts. Microscopically, they were ill-defined nodules composed of plump spindle cells and round neoplastic cells with abundant, densely eosinophilic cytoplasm and eccentric nuclei resembling rhabdomyoblasts. Neoplastic cells demonstrated infiltrative growth, including foci of perineural invasion. Immunohistochemistry demonstrated invariable co-expression of keratins, endothelial markers (CD31 and/or ERG), and FOSB. In conclusion, penile PHE is rare but should be considered in the differential diagnosis of penile lesions with spindle cell and/or rhabdomyoblast-like morphology affecting young to middle-aged adult patients.

Background Pseudomyogenic hemangioendothelioma (PHE) is a rare, locally aggressive vascular tumor. Less than 200 cases of PHE have been reported. Surgery is the cornerstone of PHE treatment, and the data on systemic treatment is limited. Methods A retrospective multicenter study was conducted on patients with PHE between January 2016 to June 2024. The clinical characteristics were summarized and the efficacy and safety of the GD regimen (gemcitabine and docetaxel) were evaluated. The primary end point was progression-free survival (PFS). Secondary end points included overall survival (OS), objective response rate (ORR), disease control rate (DCR), and adverse events (AEs). Results 16 patients were identified, with a male/female ratio of 7:1. The average age at diagnosis was 33 years. 43.8% of cases had multifocal lesions involved. The incidence of metastasis was higher than that of recurrence (43.8% vs. 18.8%). The median OS was not reached. 9 patients received chemotherapy. Among them, 6 patients were treated with GD and most of them (5/6, 83.3%) were palliative. In this palliative subgroup, 1-year PFS rate was 80.0% (4/5), with an ORR of 60% (3/5), and a DCR of 100% (5/5). Grade ≥ 3 AEs were reported in 3 patients, all classified as grade 3, without impacting the continuation of chemotherapy after symptomatic management. Conclusions Gemcitabine and docetaxel demonstrated satisfactory efficacy and acceptable safety in PHE patients; however, clinical trials and large-scale studies are needed to validate these results.

Background Pseudomyogenic hemangioendothelioma (PHE) is an unusual vascular tumor of intermediate malignancy that rarely metastasizes and tends to arise in the lower limbs of young adults and children. Histologically, PHE shows fascicular proliferation of eosinophilic spindle cells and/or epithelioid cells showing “pseudomyogenic” morphology. Immunohistochemically, PHE is usually positive for vimentin, cytokeratin, CD31 and ERG. Method We examined FOSB immunohistochemistry (IHC) in 27 cases consisting of 4 PHE and its histologic mimics including 6 epithelioid hemangioendotheliomas (EHE), 8 angiosarcomas (AS), 4 Kaposi sarcomas (KS) and 5 epithelioid sarcomas (ES). In addition, we performed IHC of CAMTA1 which has recently been established as a useful marker of EHE. We elucidated the diagnostic utility of FOSB IHC in the differential diagnosis of PHE and its histological mimics and also examined the usefulness of FOSB and CAMTA1 IHC combination in the differential diagnosis of the tumors. Results IHC revealed diffuse and strong FOSB expression in all PHE cases, while the other tumor types demonstrated limited, weak or no FOSB expression. All EHE cases exhibited diffuse and moderate to strong expression of CAMTA1. All tumor types except for EHE showed limited, weak or no CAMTA1 reactivity. Conclusions Diffuse and strong FOSB expression was specific for PHE in the current series and FOSB IHC is an effective tool for differentiating between PHE and its histological mimics. Moreover, the combination of FOSB and CAMTA1 IHC is useful for distinguishing PHE from EHE.