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Pseudomyogenic hemangioendothelioma (PMHE) is a rare vascular neoplasm with an intermediate to low-grade malignant potential. Only 5% of PMHEs occur in the head and neck. This tumor exhibits different histological patterns and mimics other vascular tumors, myoid tumors, or carcinomas. The distinction between these tumors can be a very challenging situation for pathologists. In this article, we report the first case, to our knowledge, of PMHE arising in the maxillary sinus, to highlight this uncommon entity and discuss differential diagnoses.

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.

Osseous vascular anomalies can be characterized as vascular tumors or malformations. Classification is vital for prognosis and treatment. Much remains unknown about conditions such as Gorham-Stout disease. Treatments target the proposed genetic pathways such as PI3KCA/AKT/mTOR pathway.

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.

OBJECTIVE: 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.

Pseudomyogenic hemangioendothelioma (PMH) is a rare vascular tumor that occurs in young mostly male patients. Seventy percent of PMH cases are multifocal and 25% involve bones. PMH is an indolent tumor with mild local aggressiveness and an unclear pathology. Only two cases of spontaneous regressive bone PMH have been reported. Here, we report the case of a 17-year-old boy with a multifocal bone PMH diagnosed from a chronic pain in his left knee. The PMH affected the right scapula, both humeri, the right olecranon, the second metacarpal bone, the second and fourth right ribs, the thoracic and lumbar spine, the pelvic ring, the left and right femoral neck, and the left patella. Every lesion presented with a lobulated, lytic pattern, sometimes with a peripheral sclerotic rim. MRI showed a tissue lesion with a low intensity on T1-weighted sequences and high intensity on T2-weighted sequences. Enhancement of T1 gadolinium fat-saturated sequences was bright. After discussion, a national specialized board decided to actively monitor the patient and start general chemotherapy in the case of progression. The disease was stable at 3 and 6 months and showed signs of regression at 1 year, which was further confirmed at 2 years. CT scan and MRI highlighted a progressive filling of the tumor with cancellous bone and a regression of the tissue contingent. This case report highlights to a new therapeutic approach for indolent PMH that does not prevent further treatment in the case of progression.

Pseudomyogenic hemangioendothelioma (PMH) can be a challenge for diagnosis and might be confused with other tumors, such as epithelioid sarcoma. Here we present a case and a systematic review of the literature to identify and discuss PMH treatment in primary bone involvement. A 25-year-old woman was referred for bone pain (10/10) in the left lower limb. Magnetic resonance imaging (MRI) showed multiple bone lesions (left femur, tibia, patella, ankle, and foot) with well-defined borders without signs of local aggressiveness. Positron Emission Tomography-Computed Tomography (PET-CT) showed multiple metabolic musculoskeletal lesions in the left lower limb. A CT scan-guided biopsy was performed. Histological and immunohistochemical findings confirmed the diagnosis of PMH. After treatment with intravenous pamidronate (90 mg/monthly), the patient had clinical improvement, mild pain 2/10 without the use of non-steroidal anti-inflammatory drugs or opiates. Follow-up was assessed by MRI and PET-CT. PET-CT showed metabolic resolution of most of the bone and muscular lesions and a significant improvement of the femoral lesion. MRI showed that the lesions in the left femur, tibia, and foot had a marked decrease in size without intravenous post-contrast enhancement and smaller lesions had disappeared. After a 3-year follow-up, PET-CT showed no metabolically active images. Literature review identified 31 records including 58 clinical cases of PMH with primary bone involvement and treatment description for qualitative analysis. Most lesions (69%) were treated by local excision or curettage. In addition, amputations were performed in a significant percentage of cases (20.7%). In the last years, mTOR inhibitors (n = 7) and anti-resorptive treatments (n = 4) were considered as alternative treatment options, especially in multifocal lesions.

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

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.