Establishment and characterization of a patient-derived solitary fibrous tumor/hemangiopericytoma cell line model.

Solitary fibrous tumor/Hemangiopericytoma (SFT/HPC) is a rare subtype of soft tissue sarcoma harboring NAB2-STAT6 gene fusions. Mechanistic studies and therapeutic development on SFT/HPC are impeded by scarcity and lack of system models. In this study, we established and characterized a novel SFT/HPC patient-derived cell line (PDC), SFT-S1, and screened for potential drug candidates that could be repurposed for the treatment of SFT/HPC. Immunohistochemistry profiles of the PDC was consistent with the patient's tumor sample (CD99+/CD34+/desmin-). RNA sequencing, followed by Sanger sequencing confirmed the pathognomonic NAB2exon3-STAT6exon18 fusion in both the PDC and the original tumor. Transcriptomic data showed strong enrichment for oncogenic pathways (epithelial-mesenchymal transition, FGF, EGR1 and TGFß signaling pathways) in the tumor. Whole genome sequencing identified potentially pathogenic somatic variants such as MAGEA10 and ABCA2. Among a panel of 14 targeted agents screened, dasatinib was identified to be the most potent small molecule inhibitor against the PDC (IC50, 473 nM), followed by osimertinib (IC50, 730 nM) and sunitinib (IC50, 1765 nM). Methylation profiling of the tumor suggests that this specific variant of SFT/HPC could lead to genome-wide hypomethylation. In conclusion, we established a novel PDC model of SFT/HPC with comprehensive characterization of its genomic, epigenomic and transcriptomic landscape, which can facilitate future preclinical studies of SFT/HPC, such as in vitro drug screening and in vivo drug testing.

Infantile (congenital) anaplastic intracranial solitary fibrous tumor/hemangiopericytoma-A case report with brief literature review.

Solitary fibrous tumor/hemangiopericytoma (SFT/HPC) is a rare primary central nervous system (CNS) tumor, included in the World Health Organization (WHO) 2016 classification. Very few cases have been described in the literature so far, especially the infantile type. It is a mesenchymal tumor of the fibroblastic type, characterized by the fusion of NAB 2 and STAT 6 genes. A 10-month-old boy presented to our neurosurgery department with complaints of increasing head circumference since 1 month of age. The magnetic resonance imaging (MRI) showed a space-occupying lesion measuring 8.2 cm × 7 cm × 6.9 cm in the fronto-temporo-parietal region with a clinical diagnosis of glioma/atypical teratoid rhabdoid tumor (ATRT). The microscopy revealed a spindle cell tumor arranged in a patternless pattern with variable cellularity, increased mitosis, and areas of coagulative necrosis. The immunohistochemistry showed vimentin, CD 34, STAT6, CD99 positivity whereas Glial fibrillary acidic protein, Epithelial membrane antigen, and S-100 negativity. Hence, a diagnosis of anaplastic SFT/HPC (grade-III) was rendered. The patient improved after gross total resection (GTR). The primary intracranial congenital SFT/HPC are extremely rare, often a clinico-radiologically misdiagnosed entity. Thus, the immunohistochemistry/molecular study in addition to histology is mandatory for accurate diagnosis.

Primary intranasal perivascular wall tumors in 2 cats.

Perivascular wall tumors (PWTs) are common well-known canine mesenchymal tumors. The term PWT has not yet been applied to cats; only 2 cases of feline soft tissue hemangiopericytomas (HEPs) are available. In human medicine, sinonasal HEP-like tumor/glomangiopericytoma (SHPCL/GP) and intranasal solitary fibrous tumor (SFT) are well-known mesenchymal tumors with staghorn vasculature and low malignant potential; however, these entities have not been described in small animals. We describe here the pathologic and immunohistochemical features of 2 cases of feline intranasal mesenchymal tumors consistent with PWTs and resembling human SHPCL/GP (case 1), and human intranasal SFT (case 2). Both cats developed intranasal, unilateral, polypoid, expansile neoplasms with a mostly patternless growth of spindle cells, minimal stroma, and prominent staghorn vessels. The stroma was PAS negative, which excludes a glomus tumor. Immunohistochemistry identified diffuse vimentin and PDGFRß expression. Case 1 was α-SMA positive (as is human SHPCL/GP); case 2 was negative (as is human intranasal SFT). Both tumors were incompletely excised, leading to recurrence in case 1. Case 2 was lost to follow up. To our knowledge, intranasal PWTs have not been reported previously in cats. The frequency of the lesions is not known, but awareness of these entities may assist in their recognition and better characterization in the future.

Intracranial anaplastic solitary fibrous tumor/hemangiopericytoma: immunohistochemical markers for definitive diagnosis.

Intracranial anaplastic hemangiopericytoma (AHPC) is a rare and malignant subset of solitary fibrous tumor/hemangiopericytoma (SFT/HPC) as per the WHO 2016 Classification of Tumors of the Central Nervous System. AHPC portends a poor prognosis and is associated with higher rates of recurrence/metastasis in comparison with SFT/HPC. Accordingly, it is critical to continue to define the clinical course of patients with AHPC and in so doing further refine clinicopathologic/immunohistochemical (IHC) criteria needed for definitive diagnosis. Herein, we describe clinical/histological characteristics of six patients with AHPC. In addition, we reviewed and analyzed the expression of various IHC markers reported within the literature (i.e., a total of 354 intracranial SFT/HPCs and 460 meningiomas). Histologically, tumors from our six patients were characterized by a staghorn-like vascular pattern, mitotic cells, and strong nuclear atypia. Immunohistochemically, all tumors displayed positive nuclear staining for STAT6; other markers, including CD34 and Bcl-2, were expressed only in three patients. Analysis of IHC expression patterns for SFT/HPC and meningioma within the literature revealed that nuclear expression of STAT6 had the highest specificity (100%) for SFT/HPC, followed by ALDH1 (97.2%) and CD34 (93.6%). Of note, SSTR2A (95.2%) and EMA (85%) displayed a high specificity for meningioma. Anaplastic SFT/HPC is a tumor with poor prognosis that is associated with higher rates of recurrence and metastasis in comparison with SFT/HPC. Given that anaplastic SFT/HPC requires more aggressive treatment than meningioma despite of a similar presentation on imaging, it is crucial to be able to distinguish between these tumors.

Metastatic intracranial solitary fibrous tumors/hemangiopericytomas: description of two cases with radically different behaviors and review of the literature.

Solitary fibrous tumor/hemangiopericytoma with primary tumor location in the central nervous system accounts for less than 1% of all central nervous system tumors. Despite the relatively indolent clinical course, extracranial metastases are reported in 28% of cases. In recent years, NAB2-STAT6 gene fusion has been recognized as the pathognomonic molecular feature of solitary fibrous tumor/hemangiopericytoma and STAT6 immunohistochemistry has been shown to be a sensitive and specific surrogate for the identification of the gene fusion in these patients. Here we report two cases of patients who experienced occurrence of diffuse extracranial metastases several years after successful surgery for an intracranial solitary fibrous tumor/hemangiopericytoma. In the first patient, the metastases had maintained similar histological features to the primary tumor; in contrast, in the second case, a dedifferentiation occurred with loss of expression of CD34 and Bcl-2. These different histological features were associated with radically different behaviors. Whereas the first case experienced an indolent course of the disease, the second patient had a rapid disease progression and deterioration of clinical conditions. The molecular imaging findings in these two cases and the role of functional imaging for tumor detection, disease staging and monitoring in this rare cancer are also discussed. Recurrences and metastases maintained high expression of somatostatin receptors confirmed by somatostatin receptor imaging in the first case. In contrast, in the second patient, the abrupt transition into a highly aggressive form was associated with the absence of somatostatin receptors at 111In Pentetreotide scan and intense hypermetabolism at 18F-FDG PET.

A DSTYK mutation activates ERK1/2 signaling to promote intraspinal dissemination in a case of solitary fibrous tumor/hemangiopericytoma.

Intracranial solitary fibrous tumors/hemangiopericytomas (SFT/HPCs) are vascular tumors that have a high rate of local recurrence and extracranial metastases. Intradural extramedullary spinal dissemination of intracranial SFT/HPC is extremely rare. There is a paucity of data available to elucidate the molecular mechanisms of intraspinal dissemination of intracranial SFT/HPC. Herein, we presented a case of intracranial SFT/HPC with intraspinal metastasis. The resected tumor specimens were enrolled in a clinical sequencing program, including whole-exome and transcriptome sequencing. By comparing genomic sequencing data of the intracranial tumors with intraspinal metastasis, we established the somatic mutational profiles of these tumors. Clonality analysis revealed a distinct subclonal structure in the intracranial tumor and its intraspinal metastasis, which might reflect the possibility of intratumoral clonal selection and evolution during the process of tumor dissemination. Through bioinformatics analysis and Sanger sequencing validation, a DSTYK mutation (Met296Ile) was identified as a candidate driver of intraspinal metastasis in this SFT/HPC case. Further, an intracranial tumor-derived SFT/HPC cell line, HPC3, was established to explore the mechanisms of the DSTYK mutation in promoting SFT/HPC metastasis. Based on the HPC3 cell model, we found that the DSTYK mutation promoted cell migration and invasion of HPC3 cells via activation of ERK1/2 signaling, which was inhibited by the MEK/ERK inhibitor AZD6244. The DSTYK mutation was also shown to upregulate the expression of two metastasis-related molecules: MMP2 and MMP9 in HPC3 cells; however, this effect was attenuated by AZD6244 treatment. Therefore, the DSTYK mutation may activate ERK1/2/MMP2/9 signaling to promote tumor cell metastasis in SFT/HPC. In conclusion, our study revealed the potential role of DSTYK mutation in the regulation of intraspinal metastasis of SFT/HPC, which might provide new biological insights into this rare disease.

A case of solitary fibrous tumor/hemangiopericytoma in the central nervous system with papillary morphology.

This report describes the clinicopathological findings of a solitary fibrous tumor (SFT)/hemangiopericytoma (HPC) of the central nervous system in a 59-year-old man with space-occupying lesions on both the left anterior basicranial and on the top tail of falx cerebri. The tumor showed small quantities of solid papillary areas and a prominent papillary structure, where atypical cells were compactly arranged along the fibrovascular core. The tumor cells of both components showed nuclear relocalization of the signal transducer and activator of transcription 6 protein, with very high specificity and sensitivity for the diagnosis of SFT/HPC. In the literature, only three cases of SFTs with a papillary pattern have been reported, but this case showed a complete papillary pattern. "Papillary" SFT/HPC is a rare morphological variant of SFTs/HPCs, and its differential diagnosis among intracranial tumors is an important factor which clinicians should bear in mind during diagnosis.

Pathological prognostic markers in central nervous system solitary fibrous tumour/hemangiopericytoma: Evidence from a small series.

BACKGROUND: Primary central nervous system (CNS) solitary fibrous tumour/hemangiopericytoma (SFT/HPC) is a rare neoplasm and its classification criteria have been redefined by the latest WHO Classification of CNS Tumours. Outcome can vary significantly among patients, thus reliable prognostic markers are warranted. METHODS: Primary CNS SFT/HPC diagnosed at the Pathology Unit of our Institution between 2006 and 2016 were retrospectively collected. Tumour grade along with immunohistochemistry for Ki67, STAT6, PHH3, CD34 and Bcl-2 were assessed. TERT promoter status was evaluated by Sanger sequencing. RESULTS: Fifteen SFT/HPC were analysed: 9/15 (60%) female, median age at diagnosis 60 (range: 10-67). Six (40%) cases showed a SFT phenotype and mean H&E-mitotic count was 4.8/10 HPF. Tumour grade was I in 6, II in 4 and III in 5 cases. Mean PHH3-mitotic count was higher than H&E count (8.4 versus 4.8/10 HPF), but it would have determined a change in tumour grade in a sole case. Nuclear staining for STAT6 was present in 14/15 (93.3%). CD34 and Bcl-2 expression rates were lower in higher grade tumours. TERT promoter was mutated in two cases. Median follow up time was 2.4 years (6 months-7.4 years) and 5/15 (33%) patients developed local disease recurrence. Partial resection (p = 0.0185), higher WHO grade (p = 0.038), lower CD34 (p = 0.038) and Bcl-2 (p = 0.010) expressions were significantly associated with a poorer disease-free interval. CONCLUSIONS: WHO grade is the main prognostic tool in CNS SFT/HPC, but it could be integrated by other markers, like CD34 and Bcl-2, in the clinical practice. The relevance of TERT promoter mutations in this subset of CNS tumours needs further evaluation.

Meningeal solitary fibrous tumor/hemangiopericytoma: Emphasizing on STAT 6 immunohistochemistry with a review of literature.

BACKGROUND: The 2016 central nervous system (CNS) World Health Organisation (WHO) Update has merged the entities of meningeal solitary fibrous tumor (SFT) and hemangiopericytoma (HPC) into a single entity based on the presence of the nerve growth factor 1A (NGFI-A) binding protein 2 (NAB2)- signal transducer and activator of transcription 6 (STAT6) gene fusion in these tumors. Immunohistochemical (IHC) staining with STAT6 results in a strong nuclear positivity confirming the diagnosis. Meningeal SFT/HPCs are currently histologically graded according to a three-tiered system. Grade I (SFT phenotype) is benign, whereas grades II and III (HPC phenotype) are malignant and require radiotherapy in addition to gross total resection. OBJECTIVES: The objectives were to review the cases diagnosed as meningeal SFT or HPC between 2010 and 2017 and classify them into SFT (grade I) or HPC (grades II and III) phenotypes; to confirm the diagnosis by performing STAT6 immunohistochemistry; and to observe and record the histological features in detail and correlate the tumor grades with their behavior. The published literature on the subject was also reviewed. MATERIALS AND METHODS: A total of 21 cases diagnosed between 2010 and 2017 as meningeal SFT or HPC were included in the study. All cases were reviewed by the authors and were categorized and graded according to histologic phenotype and mitotic count. STAT6 immunohistochemistry was performed in all the cases. The epidemiological data and histologic findings in each case were recorded in detail. The follow-up of patients was obtained. RESULTS: Fifteen patients were males and six were females. The mean age was 43.5 years. The mean tumor size was 6.8 cm. The tumor specimens in 20 out of 21 cases corresponded to the HPC phenotype, of which 6 were in grade II while 14 were in grade III. Thus, over 95% cases had malignant lesions. The tumor in all the 21 cases recruited for the study showed immunohistochemical positivity for SAT6, while CD34 was positive in all the 18 tumor in which it was performed. The follow-up was available in 14 of the patients. Recurrence occurred in six patients who had either a grade II or a grade III tumor and three patients died (including one patient with a grade III tumor. This patient died a month after initial resection although there was no evidence of recurrence). Radiotherapy was given to only 4 out of 14 patients in whom follow-up was available. CONCLUSION: These rare tumors need to be accurately diagnosed and optimally treated (gross total resection and radiotherapy) to improve the prognosis.

Pazopanib efficacy in recurrent central nervous system hemangiopericytomas.

INTRODUCTION: There is currently no treatment for solitary fibrous tumors/hemangiopericytomas (SFT/H) of the central nervous system recurring after multiple surgeries and radiotherapies. The NAB2-STAT6 gene fusion is the hallmark of these tumors, and upregulates Early Growth Factor, activating several growth pathways. METHODS: We treated two patients presenting pluri-recurrent meningeal SFT/H with Pazopanib, a broad-spectrum tyrosine kinase inhibitor. We analyzed the exome and RNA sequencing data of one of them and, in addition to another meningeal SFT/H, compared it to the transcriptomic profiling of 5 systemic SFT/H. RESULTS: A dramatic clinical and radiological response was observed in both cases, respectively 84 and 43% decrease after 3 months. As a comparison, Pazopanib has only a stabilizing effect in systemic SFT/H. Indeed, central nervous system SFT/H show overexpression of different tyrosine kinases targeted by Pazopanib. CONCLUSIONS: Two consecutive patients with untreatable central nervous system SFT/H showed a spectacular partial response to Pazopanib, an unprecedented result in SFT/H. This result could be explained by differences in expression profiles and calls for a confirmation in a larger cohort of patients.

Association between programmed cell death ligand-1 expression and extracranial metastasis in intracranial solitary fibrous tumor/hemangiopericytoma.

BACKGROUND: Intracranial solitary fibrous tumor/hemangiopericytoma (SFT/HPC) often shows extracranial metastasis, and treatment options are very limited. Immune-checkpoint molecules have not been studied well in SFT/HPCs, and their role in intracranial SFT/HPCs remains unclear. METHODS: We investigated the expression of programmed cell death-1 (PD-1), programmed cell death ligand-1 (PD-L1), and tumor-infiltrating lymphocytes (TIL) in 16 patients of intracranial SFT/HPC by immunohistochemistry to determine if correlation with prognosis exists. RESULTS: Median overall survival (OS) of 16 patients was 9.2 years, and median follow-up of alive patients was 9.9 years. Recurrence was observed in 13 (81.3%) patients, and extracranial metastasis were observed in 6 (37.5%). PD-L1 expression was observed in all 16 tumors, whereas PD-1 expression was observed in 2. CD3 and CD8 expressions were observed in TILs in 12 and 13 patients respectively. Although the ratio of PD-L1 positive-tumor cells was not associated with OS, progression-free survival, or metastasis-free survival (MFS), diffuse staining of PD-L1 showed a trend toward shorter time to treatment failure (TTF: time to either extracranial metastasis or death) (p = 0.072). Similarly, the intense staining of PD-L1 was associated with shorter MFS (p = 0.0084) and TTF (p = 0.033). CD3 or CD8 expression was not associated with any of the prognostic parameters. In the combined analysis of PD-L1 and CD8, diffuse PD-L1 staining coupled with no or sparse CD8 expression was significantly associated with a shorter TTF (p = 0.005) and showed a trend toward shorter MFS (p = 0.0611). CONCLUSIONS: PD-L1 is frequently expressed in intracranial SFT/HPCs, and diffuse or intense PD-L1 expression might be associated with the early occurrence of extracranial metastases.

Reappraisal of morphological and immunohistochemical spectrum of intracranial and spinal solitary fibrous tumors/hemangiopericytomas with impact on long-term follow-up.

BACKGROUND: Hemangiopericytomas (HPCs) and solitary fibrous tumors (SFTs) are unique entities in the central nervous system (CNS) and even rarer in the spine with propensity to recurrence and metastasis. Both these tumors were detected to share the NAB2-STAT6 fusion gene with frequent morphologic overlap that necessitated the need for the combined term SFT/HPC in the CNS by the World Health Organization (WHO) in 2016. AIMS: This study aims to describe the clinical outcome of intracranial and spinal SFT/HPCs based on detailed histomorphologic and immunohistochemical features. MATERIALS AND METHODS: A retrospective analysis of these tumors was conducted over a period of 10 years from January 2006 to January 2017 at our institute. Based on the elaborative assessment of morphology and immunohistochemistry, these tumors were categorized into three grades as per WHO criteria. RESULTS: A total of 13 cases were encountered involving mainly extra-axial and supratentorial regions. Among intracranial HPCs, anaplastic subtypes constituted significantly higher proportion (39%) when compared with peripheral HPCs. Peculiar morphological patterns like micropapillae and pseudoangiomatous arrangement of tumor cells were observed in high-grade tumors. A panel of immunomarkers were used to confirm the diagnosis and rule out other mimickers. Gross total resection was achieved in 54% (7/13) of the cases with local recurrence observed in 31% (4/13). Grade II tumors showed recurrence in 28% cases. No case showed distant metastasis. CONCLUSION: To conclude, not just clinical parameters but morphologic features such as unusual patterns, mitosis, and proliferative index also play a pivotal role in predicting the clinical behaviour of SFT/HPC.

Orbital Hemangiopericytoma in 68Ga-Prostate-Specific Membrane Antigen-HBED-CC PET/CT.

A 76-year-old man with biochemical relapse of prostate cancer underwent Ga-prostate-specific membrane antigen PET/CT. Besides a local lymph node metastasis, a nodular structure inside the left orbit caudal to the optic nerve showed increased uptake. A metastasis in this location is unlikely. The subsequently performed MRI showed the structure being T1 hypointense, T2 indifferent, and strongly gadolinium contrast agent enhancing. Histopathologic examination after surgical removal identified the tumor as hemangiopericytoma, which rarely occurs in the orbit. Regarding the intense uptake observed, prostate-specific membrane antigen-targeting PET tracers could bear potential for staging purposes of this tumor entity.

Analyses of prognosis-related factors of intracranial solitary fibrous tumors and hemangiopericytomas help understand the relationship between the two sorts of tumors.

Increasing evidence has suggested a close relationship between solitary fibrous tumors (SFTs) and hemangiopericytomas (HPCs) in the central nervous system (CNS). However, CNS SFTs differentiate from HPCs in their clinical behavior and patient prognoses. Analyses of prognosis-related factors can help clarify the relationship between SFT and HPC. The intracranial SFT and HPC cases treated in our departments from January 2002 to December 2012 were retrospectively reviewed. The SFT and HPC cases were also combined into an SFT/HPC group. The factors associated with patient progression-free survival (PFS) and overall survival (OS) were statistically analyzed using uni- and multivariate analyses. Fifty-eight intracranial SFT/HPC patients including 38 SFT patients and 20 HPC patients were treated during this period. The "Marseille grading" evaluated upon the histological aggressive phenotypes was applied in this study. The grading reflected a malignant progression ranging from "conventional" SFTs (grade I) to WHO III HPCs (grade III), and grade was negatively correlated with the PFS and OS of the SFT, HPC and SFT/HPC patients (P < 0.05).The multivariate analyses revealed that gross total resection (GTR) was significantly positively correlated with PFS and OS in the SFT, HPC and SFT/HPC patients and that radiotherapy was significantly positively correlated with PFS in the HPC and SFT/HPC patients (P < 0.05). In conclusion, the intracranial SFTs and HPCs share common prognostic factors including extent of surgery and pathology, moreover, the histological grading of the aggressive phenotypes supports the unifying of the CNS SFT and HPC into one tumor entity of SFT/HPC.

Multifocal Congenital Hemangiopericytoma.

Congenital hemangiopericytoma (HPC) is a rare mesenchymal tumor with less aggressive behavior and a more favorable prognosis than similar tumors in adults. Multifocal presentation is even less common than isolated HPC and hence its clinical and histologic recognition may be challenging. A newborn infant with multifocal congenital HPC causing severe deformity but with a favorable outcome after chemotherapy and surgical removal is reported.

Hemangiopericytomas in the Central Nervous System: A Multicenter Study of Korean Cases with Validation of the Usage of STAT6 Immunohistochemistry for Diagnosis of Disease.

BACKGROUND: Hemangiopericytoma (HPC) in the central nervous system (CNS) is a rare disease with distinctive biological/clinical characteristics compared with meningioma. METHODS: Cases of HPCs of the CNS were collected, and clinicopathological records were retrospectively reviewed and analyzed. Immunohistochemistry (IHC) for proliferative markers (Ki-67, PHH3) and STAT6 were performed. RESULTS: A total of 140 cases were collected, with mean follow-up of 77 months (median 58.8 months; range 0.53-540.5 months). 1-, 5-, 10-, and 20-year survival rates were 99.1, 94.0, 74.4, and 61.9 %, respectively. Thirty-nine patients (27.9 %) had recurrent disease. Mean and median times to recurrence were 62.9 and 47.3 months with 1-, 5-, 10-, and 20-year recurrence-free survival rates of 98.3, 78.3, 50.1, and 11.0 %, respectively. Thirteen patients (9.3 %) developed extracranial metastases. No adjuvant radiation therapy, higher histologic grades, failure of gross-total resection, and cases with gamma-knife surgery (GKS) were factors associated with shorter disease-free survival (log-rank test, p = 0.02, 0.00, 0.02, 0.00), among which high histologic grade and cases with GKS were significant in multivariable analysis. Strong nuclear STAT6 expression was noted in HPCs in 62 cases of HPCs (60/62, 96.8 %), whereas diffuse weak positivity was demonstrated in all meningioma cases. CONCLUSIONS: The survival rate in patients with HPC of the CNS is comparable to that of previously reported series. Recurrence remains a critical clinical issue of the disease. Identification of NAB2-STAT6 fusion transcript with surrogate IHC marker is a valuable diagnostic tool in the differential diagnosis of the disease.

CD34-positive infantile myofibromatosis: Case report and review of hemangiopericytoma-like pattern tumors.

We describe a case of CD34-positive infantile myofibromatosis with hemangiopericytoma-like pattern. A 2-day-old Japanese boy presented with multiple hemispherical nodules on the extremities and back. There was a biphasic histological growth in the dermis, accompanied by a hemangiopericytoma-like pattern with antler-like branching vessels. Tumor cells were oval to spindle-shaped myoid cells with bland appearance. Immunohistochemically, vimentin, calponin and CD34 were positive, while α-smooth muscle actin, h-caldesmon, HHF35 and desmin were negative. Although CD34 was positive, the present case could be diagnosed as infantile myofibromatosis. Myopericytoma, myofibroma/myofibromatosis, glomus tumor, glomangiopericytoma and angioleiomyoma share a continuous spectrum of benign hemangiopericytoma-like pattern tumors. Myofibroma/myofibromatosis is nearly included in myopericytoma among pericytic (perivascular) tumors, and could be positive for CD34. Several immunohistochemical panels of smooth muscle markers are needed for the diagnosis of pericytic (perivascular) tumors.

Paediatric and adult soft tissue sarcomas with NTRK1 gene fusions: a subset of spindle cell sarcomas unified by a prominent myopericytic/haemangiopericytic pattern.

Neoplasms with a myopericytomatous pattern represent a morphological spectrum of lesions encompassing myopericytoma of the skin and soft tissue, angioleiomyoma, myofibromatosis/infantile haemangiopericytoma and putative neoplasms reported as malignant myopericytoma. Lack of reproducible phenotypic and genetic features of malignant myopericytic neoplasms have prevented the establishment of myopericytic sarcoma as an acceptable diagnostic category. Following detection of a LMNA-NTRK1 gene fusion in an index case of paediatric haemangiopericytoma-like sarcoma by combined whole-genome and RNA sequencing, we identified three additional sarcomas harbouring NTRK1 gene fusions, termed 'spindle cell sarcoma, NOS with myo/haemangiopericytic growth pattern'. The patients were two children aged 11 months and 2 years and two adults aged 51 and 80 years. While the tumours of the adults were strikingly myopericytoma-like, but with clear-cut atypical features, the paediatric cases were more akin to infantile myofibromatosis/haemangiopericytoma. All cases contained numerous thick-walled dysplastic-like vessels with segmental or diffuse nodular myxohyaline myo-intimal proliferations of smooth muscle actin-positive cells, occasionally associated with thrombosis. Immunohistochemistry showed variable expression of smooth muscle actin and CD34, but other mesenchymal markers, including STAT6, were negative. This study showed a novel variant of myo/haemangiopericytic sarcoma with recurrent NTRK1 gene fusions. Given the recent introduction of a novel therapeutic approach targeting NTRK fusion-positive neoplasms, recognition of this rare but likely under-reported sarcoma variant is strongly encouraged.

Ultrastructure and histogenesis of the acral calcified angioleiomyoma.

We studied the ultrastructure, immunohistochemistry, and histogenesis of the acral calcified angioleiomyoma, observing three concentric zones: (a) pseudocapsular, thin, with spindle-shaped stromal cells (SCs), presenting scarce organelles and expressing CD34, (b) muscular, forming a ring, with smooth muscle cells of heterogenous phenotype (mainly in quantity and thickness of filaments, and in expression of h-caldesmon, αSMA, and desmin), and (c) central, extensive, calcified (spicular and/or star-shaped calcium deposits around collagen fibers), with pericytic involutive vasculature. The intratumoral vessels were thick (several layers of perivascular cells, with a continuum of phenotypes, resembling myopericytoma vessels) and thin (slit-like channels), without adventitial SCs or elastic material. The extratumoral vessels showed adventitial SCs (which contribute to form the tumor pseudocapsule), hyperplasia of the media and intima layers, and/or occlusion of the lumen by a wide, homogenous fibrotic central zone. Histogenetically, the collagenous matrix may act as a mineralization substrate and the calcifying modified pericytes as inductors; intratumoral vessels may originate from the peritumoral vessels or from the vessel where the tumor develops; and extratumoral vessel modifications, mimicking tumor features, concur with a minor repetitive trauma pathogenesis.