Neurofibroma with glomus-like bodies: A novel association-Thoughts about origin.

A neurofibroma with focal glomus-like body differentiation is an unusual phenomenon recently encountered in an excision specimen from the right lateral distal forearm of a 26-year-old man. Glomus cells are modified smooth muscle cells normally present in glomus-like bodies but can also be found in glomus tumors (GT) or lesions considered in the spectrum of GT, including myopericytoma, myofibroma, and angiolipoma. Neurofibromas are peripheral nerve sheath tumors derived from the neural crest cells. While both GT and its variants and neurofibroma are thought to be derived from different cell types, there is growing evidence that glomus cells have a neural crest origin. This is based on multiple theories, with some overlapping pathways, including neural crest cell differentiation, Schwann cell reprogramming, VEGF expression, and NF1 gene biallelic inactivation. This report adds to the growing evidence of possible neural crest origin for glomus cells and would help explain finding glomus-like bodies scattered through a neurofibroma.

Loss-of-function variants in GLMN are associated with generalized skin hyperpigmentation with or without glomuvenous malformation.

BACKGROUND: Inherited hyperpigmented skin disorders comprise a group of entities with considerable clinical and genetic heterogenicity. The genetic basis of a majority of these disorders remains to be elucidated. OBJECTIVES: This study aimed to identify the underlying gene for an unclarified disorder of autosomal-dominant generalized skin hyperpigmentation with or without glomuvenous malformation. METHODS: Whole-exome sequencing was performed in five unrelated families with autosomal-dominant generalized skin hyperpigmentation. Variants were confirmed using Sanger sequencing and a minigene assay was employed to evaluate the splicing alteration. Immunofluorescence and transmission electron microscopy (TEM) were used to determine the quantity of melanocytes and melanosomes in hyperpigmented skin lesions. GLMN knockdown by small interfering RNA assays was performed in human MNT-1 cells to examine melanin concentration and the underlying molecular mechanism. RESULTS: We identified five variants in GLMN in five unrelated families, including c.995_996insAACA(p.Ser333Thrfs*11), c.632 + 4delA, c.1470_1473dup(p.Thr492fs*12), c.1319G > A(p.Trp440*) and c.1613_1614insTA(Thr540*). The minigene assay confirmed that the c.632 + 4delA mutant resulted in abolishment of the canonical donor splice site. Although the number of melanocytes remained unchanged in skin lesions, as demonstrated by immunofluorescent staining of tyrosinase and premelanosome protein, TEM revealed an increased number of melanosomes in the skin lesion of a patient. The GLMN knockdown MNT-1 cells demonstrated a higher melanin concentration, a higher proportion of stage III and IV melanosomes, upregulation of microphthalmia-associated transcription factor and tyrosinase, and downregulation of phosphorylated p70S6 K vs. mock-transfected cells. CONCLUSIONS: We found that loss-of-function variants in GLMN are associated with generalized skin hyperpigmentation with or without glomuvenous malformation. Our study implicates a potential role of glomulin in human skin melanogenesis, in addition to vascular morphogenesis.

A group of skin conditions known as 'inherited hyperpigmented skin disorders' includes some diseases with different clinical and genetic traits. The genetic basis of the majority of these diseases is not understood. To identify the gene responsible for a disease that causes darker patches of skin (hyperpigmentation) with or without the abnormal growth of blood vessels and the presence of cells named glomus cells (a glomuvenous malformation), we used genetic techniques called whole-exome sequencing and Sanger sequencing in five unrelated families with this disease. We also used a technique called a 'minigene assay' to evaluate genetic alterations in a gene called GLMN, which encodes a protein called glomulin. Immunofluorescence and transmission electron microscopy (TEM) were used to determine the number of pigment-producing cells (called melanocytes) and melanosomes (where the pigment melanin is synthesized, stored and transported) in hyperpigmented skin lesions. We identified five different variants of the GLMN gene in five unrelated families. Although the number of melanocytes remained unchanged in skin lesions, TEM revealed an increased number of melanosomes. By 'switching off' the GLMN gene, we found that skin cells produced more pigment, as well as the proteins MITF and tyrosinase; they also showed a decrease in the phosphorylated protein p-p70S6 K. Overall, we found that loss-of-function mutations in GLMN caused skin hyperpigmentation with or without abnormal blood vessels. The results suggest there could be a potential role of the protein glomulin in human skin colour and blood vessel changes.

Novel ATG7::RAF1 gene fusion in malignant glomus tumor.

Glomus tumors are classified as members of the perivascular myoid family of tumors. Nearly half of these show NOTCH-gene fusions and a smaller subset has BRAF V600E mutations. Here, we report a novel ATG7::RAF1 fusion in malignant glomus tumor occurring in a 40-year-old female which has not been reported in the malignant glomus tumor before. A 40-year-old female presented with a persistent lateral heel pain and an increase in the size of a mass along the lateral ankle for nearly 10 years. Resected specimen showed a well circumscribed lesion composed of spindled and epithelioid cells with moderate nuclear atypia and mitotic figures (7/10 high-power fields) including atypical forms without any necrosis, lymphovascular, or perineural invasion. The tumor was positive for smooth muscle actin, smooth muscle myosin heavy chain, H-caldesmon, collagen type IV, and discovered on gastronintestinal stromal tumors-1 but negative for AE1/3, desmin, S-100, CD34, and CD117. RNA sequencing showed presence of ATG7-RAF1 fusion. This fusion has not been reported in the malignant glomus tumor before. Future studies on larger cohorts are needed to ascertain the biological significance of these tumors with novel gene fusions.

A Rapidly Expanding Hemorrhagic BRAF-Mutant Orbital Atypical Glomus Tumor.

A healthy 32-year-old woman presented with the acute onset of left sided eye pain, upper eyelid fullness, and binocular diplopia during light weightlifting. Examination elevated intraocular pressure, proptosis, upper eyelid ptosis, and motility deficits. CT demonstrated a well-circumscribed, homogeneous-appearing extraconal mass in the superior left orbit. The patient underwent an urgent orbitotomy with the excision of a hemorrhagic mass. Histopathology showed a glomus tumor with atypical features and hemorrhagic infarction, best classified as having uncertain malignant potential. A B-Raf proto-oncogene V600E mutation was detected with immunohistochemistry, which suggests a more aggressive tumor behavior yet presents an opportunity for targeted primary or adjunctive therapy. This is the first reported case of a B-Raf proto-oncogene-mutant atypical glomus tumor arising in the orbit.

Gastric glomus tumor on EUS-FNA-based cytology: clinicopathologic and immunohistochemical features of 4 cases, including 1 case with associated MIR143HG-NOTCH2 fusion gene.

INTRODUCTION: Gastric glomus tumor (GT) is a rare submucosal tumor for which the preoperative diagnosis can be challenging. We report the cytomorphologic and immunohistochemical features of 4 gastric GTs diagnosed by endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) cytology. MATERIALS AND METHODS: Files were searched to identify gastric GTs diagnosed by EUS-FNA between 2018 and 2021. A total of 4 cases of gastric GTs (3 men and 1 women; mean age, 60 years) were included. RESULTS: Three GTs were located in the gastric antrum and one in the gastric body. Their size ranged from 2 to 2.5 cm. Three patients presented with epigastric discomfort and one with chest wall discomfort. Rapid on-site evaluation was performed for 3 cases; the findings for all 3 were indeterminate. The smears were moderate to highly cellular and showed loose clusters of evenly distributed small- to medium-size bland tumor cells. The tumor cells had centrally located round to oval nuclei with inconspicuous nucleoli and scant to moderate amount of eosinophilic to clear cytoplasm. Examination of the cell blocks revealed branching small vessels surrounded by small- to medium-size cells. The neoplastic cells were positive for smooth muscle actin and synaptophysin and negative for AE1/AE3 and S-100. C-KIT and CD34 were variably positive. Ki-67 was <2% positive. In 1 case, the fusion panel-solid tumor (50 genes) revealed the MIR143HG-NOTCH2 fusion gene. CONCLUSIONS: Smears and cell block preparation revealed angiocentric sheets of uniform, small round to oval tumor cells with pale to eosinophilic cytoplasm, intermingled with endothelial cells. The differential diagnosis of gastric GTs on rapid on-site evaluation includes neuroendocrine tumors and epithelioid or spindled cell neoplasms. Immunohistochemical and molecular studies can be helpful in the preoperative diagnosis of gastric GT.

Oesophageal glomus tumours: rare neoplasms with aggressive clinical behaviour.

AIMS: Glomus tumours are neoplasms with perivascular smooth muscle differentiation, which rarely occur in the oesophagus and may behave aggressively in this site based upon prior case reports. This study describes the clinicopathologic features of three oesophageal glomus tumours diagnosed at two large academic institutions between 1984 and 2022. METHODS AND RESULTS: Three cases of oesophageal glomus tumours were identified. Patients included two females and one male, with an age range of 19-65 years. All three tumours behaved in a malignant fashion, with metastases to various sites (lymph nodes, lung, pericardium, pleura, diaphragm, scalp). One patient developed an aorto-oesophageal fistula, resulting in a fatal haemorrhage. Tumours ranged in size from 4.5 to 8.1 cm. Histologically, all tumours had a multinodular, perivascular growth pattern. The neoplasms showed varying degrees of cytologic atypia and spindling, elevated mitotic activity (2-12 mitotic figures per 10 high-power fields), and necrosis was seen in in two cases. All tumours expressed smooth muscle actin by immunohistochemistry, and harboured NOTCH gene alterations (MIR143::NOTCH2 fusion in two cases; NOTCH3 rearrangement and NOTCH1 point mutation in one case). An ATRX splicing mutation in exon 10 was also identified in one case. CONCLUSION: Oesophageal glomus tumours pose diagnostic challenges, given their rarity at this site, but can be recognised by their characteristic perivascular growth pattern, round central nuclei, and supportive ancillary studies. Given the propensity for aggressive behaviour in this location, we recommend management by a multidisciplinary sarcoma team for optimal outcome.

PDGFRB and NOTCH3 Mutations are Detectable in a Wider Range of Pericytic Tumors, Including Myopericytomas, Angioleiomyomas, Glomus Tumors, and Their Combined Tumors.

Pericytic tumors are subclassified as myopericytomas, myofibromas, angioleiomyomas, and glomus tumors according to the current World Health Organization classification. These pericytic tumors form a continuous morphologic spectrum, including those with combined morphology. However, to our knowledge, no widely accepted criteria for classifying tumors with combined morphology are available. Recent studies have identified platelet-derived growth factor receptor-beta (PDGFRB) gene mutations in a subset of myofibromas, myopericytomas, and myopericytomatoses but not in angioleiomyomas. NOTCH receptor 3 (NOTCH3) mutations have been reported in a subset of infantile myofibromatosis. To assess their potential role in classifying pericytic tumors, we investigated PDGFRB and NOTCH3 mutations in 41 pericytic tumors of variable morphology, including some combined forms. Our results show these mutations to be present in a variety of pericytic tumors, such as myopericytomas (PDGFRB, 3/11; NOTCH3, 4/11), myopericytomatoses (1/2; 1/2), myofibromas (3/6; 0/6), angioleiomyomas (2/13; 3/13), and glomus tumors (5/9; 1/9). Point mutations were identified in 3 tumors in PDGFRB exon 12 (Y562C, S574F, and G576S), 12 tumors in PDGFRB exon 14 (M655I, H657L, and N666K), and 9 tumors in NOTCH3 exon 25 (A1480S/T, D1481N, G1482S, T1490A, E1491K, G1494S, and V1512A). All PDGFRB mutations and NOTCH3 G1482S, T1490A, and G1494S mutations were classified as "deleterious/damaging" by ≥4 of 6 pathogenicity prediction tools in silico. Five-mutation-positive tumors, including 1 myopericytoma-angioleiomyoma, 2 myopericytomatoses-myofibroma, 1 myofibroma-myopericytoma and 1 angioleiomyoma-myopericytoma, were of combined morphology. Therefore, we found PDGFRB and NOTCH3 mutations to be detectable in a much wider variety of pericytic tumors than previously reported and confirmed myopericytomas, myofibromas, angioleiomyomas, and glomus tumors as members harboring PDGFRB or NOTCH3 mutations. Our results thus suggest that PDGFRB or NOTCH3 mutations are not useful for subclassifying members of the pericytic tumor family.

A rapidly growing cutaneous malignant glomus tumor with a CCND3 mutation.

Glomus tumors are rare mesenchymal neoplasms composed of cells resembling the glomus body. They are most frequently seen in subungual regions but have been reported to arise in almost every anatomic location. Malignant glomus tumors, also called glomangiosarcomas, of cutaneous origin are exceedingly rare with only 47 reported cases. The genetic alterations that lead to the development of cutaneous malignant glomus tumors are not well understood. Small studies report glomus tumors with mutations in glomulin (GLMN), NF1, BRAF, NOTCH, PDGFRB, KRAS, and SMARCB1. These mutations have mostly been studied in deep or visceral glomus tumors. We report a case of a cutaneous malignant glomus tumor with a CCND3 point mutation identified on next generation sequencing, without any of the previously described genetic mutations. CCND3 mutations that cause cyclin D3 amplification may prove to be targets for CDK4/6 inhibitors in the treatment of malignant glomus tumors.

Superficial GLI1-amplified mesenchymal neoplasms: Expanding the spectrum of an emerging entity which reaches the realm of dermatopathology.

Mesenchymal neoplasms with GLI1 alterations (rearrangements and/or amplification) have been reported recently in several anatomic locations, which include head and neck, soft tissue, and gastrointestinal tract. Herein, to the best of our knowledge, we describe the first three cases of superficial/subcutaneous mesenchymal neoplasm with GLI1 amplification. The neoplasms exhibited low-grade cytologic features with predominant round cell morphology, glomangioma-like areas and a rich background capillary network. There were two to three mitotic figures per 10 HPF and focal necrosis in one case. The tumors exhibited variable expression of CDK4, MDM2, STAT6, D2-40, CD56 and cyclin D1. p16 had strong and diffuse nuclear and cytoplasmic expression in two cases. Numerous other stains were negative. Fluorescence in situ hybridization detected GLI1, DDIT3, and CDK4 coamplification in all cases, while next generation sequencing did not detect a GLI1 gene fusion. The overall features were compatible with a GLI1-amplified mesenchymal neoplasm. In Case 1 a new distant skin lesion appeared 1 month after the surgery exhibiting similar morphology albeit with a higher mitotic index. In Cases 2 and 3, there is no evidence of local recurrence or systemic disease after 8 years and 1 month of follow-up, respectively. These new cases of superficial GLI1-amplified neoplasm expand its clinical spectrum and enter the realm of dermatopathology. The combination of CDK4, cyclin D1, D2-40, and p16 expression with variable MDM2, STAT6, CD56, and S100 immunoreactivity in a low-grade neoplasm with round/ovoid cytomorphology resembling a vascular or adnexal neoplasm may suggest the possibility of GLI1-amplified neoplasm.

Gastroesophageal Glomus Tumors: Clinicopathologic and Molecular Genetic Analysis of 26 Cases With a Proposal for Malignancy Criteria.

Although criteria for malignancy have been established for glomus tumors of soft tissue, there are no accepted criteria for gastroesophageal glomus tumors, the behavior of which is considered to be unpredictable. Recently, both benign and aggressive gastroesophageal glomus tumors have been shown to harbor CARMN :: NOTCH2 fusions, but, as yet, there are no described genetic features that predict clinical behavior. Here, we evaluated 26 gastroesophageal glomus tumors to investigate histologic and genetic features that might predict malignant behavior. Seventeen patients (65%) were male. The median age at presentation was 54.5 years (range: 16 to 81 y). Primary sites were stomach (25 tumors) and distal esophagus (1). The median tumor size was 4.05 cm (range: 0.8 to 19.5 cm). Tumors were composed of lobules of rounded cells with sharp borders, palely eosinophilic to clear cytoplasm, and round nuclei. All tumors involved the muscularis propria, and 12 also involved the serosal surface. Mitoses ranged from <1 to 53/10 HPF (median: 5/10 HPF). Sixteen tumors, including all 15 with mitoses ≥2/10 HPF, showed atypia (3 mild, 10 moderate, 3 severe), defined as spindle cell morphology, nuclear irregularity, nuclear size variability, enlarged nuclei, or coarse chromatin. Considering these histologic features and clinical behavior, tumors were classified as malignant (15 tumors) if they measured ≥5 cm or showed both atypia and mitoses ≥2/10 HPF, or benign (11 tumors) if these criteria were not met. Follow-up was available for 19 patients (73%; range: 1 to 15 y; median: 5.8 y), including 7 with benign tumors and 12 with malignant tumors. Two patients with malignant tumors had metastases at presentation, and 7 developed metastases subsequently. Follow-up was available for 8 of 9 patients with metastatic disease. Two were alive with disease at most recent follow-up. One underwent resection of a liver metastasis, with no subsequent metastases in 3 years of follow-up. Five patients died of metastatic disease. By immunohistochemistry, smooth muscle actin was diffusely positive in all evaluated tumors, and caldesmon and synaptophysin were positive in 94% and 73%, respectively. Sequencing identified NOTCH2 alterations in 4 benign tumors (80%) and 8 malignant tumors (80%), including CARMN :: NOTCH2 fusions in 2 benign and 5 malignant tumors. All 5 sequenced benign tumors lacked complex copy number alterations (CNAs), whereas all 10 sequenced malignant tumors showed complex CNAs, including recurrent loss of 9p21.3 (4/10, variably including CDKN2A / B and MTAP ) and ATRX inactivation (4/10). Complex CNAs were identified in all sequenced tumors that were ≥5 cm, exhibited both cytologic atypia and ≥2 mitoses/10 HPF, involved the serosa or metastasized. We propose that gastroesophageal glomus tumors ≥5 cm or with both atypia and mitoses ≥2/10 HPF should be considered malignant. Copy number analysis might be helpful in borderline cases.

PIK3CA mutation in a case of CTNNB1-mutant sinonasal glomangiopericytoma.

Glomangiopericytomas are rare, primary sinonasal tumors. The existing literature is mostly limited to reports describing the clinicopathologic characteristics of these tumors. Comprehensive genetic characterization of glomangiopericytomas remains lacking. Whole-exome sequencing of a case of glomangiopericytoma was performed under an institutional review board-approved protocol. A 69-yr-old female underwent surgical resection of a glomangiopericytoma. Whole-exome sequencing revealed somatic mutations in CTNNB1 and PIK3CA, the former previously associated with this pathology but the latter not described. Concurrent dysregulation of Wnt/ß-catenin and PI3K/AKT/mTOR signaling, secondary to mutations in these two oncogenes, may be amenable to targeted treatment with existing clinically approved drugs. Genomic characterization of glomangiopericytomas remains lacking. This study reports novel coexistence of PIK3CA and CTNNB1 mutations in a case of glomangiopericytoma that may offer insight into the pathogenesis and potential for targeted medical therapies of this rare tumor.

Clinicopathologic features and BRAF mutation status of tracheal glomus tumors - Characterization of 4 cases and the distinction from low-grade neuroendocrine tumors.

BACKGROUND: Glomus tumors are uncommon and mostly benign mesenchymal neoplasms of the perivascular family. To date, only a few cases of glomus tumors occurring in the trachea have been reported. Tracheal glomus tumors simulated low-grade neuroendocrine tumors on clinical and histomorphological examination, so the differential diagnosis between these two entities is very necessary. The latest studies showed that BRAF mutation may be associated with a malignant phenotype of glomus tumors. METHODS: We investigated the clinical, histopathologic, immunohistochemical, and BRAF V600E mutation status of four cases of tracheal glomus tumors. RESULTS: The cases showed a female predilection (male:female, 1:3) with a median age of 35.5. All of the cases had the typical morphological characteristics of glomus tumors, such as uniform round tumor cells with nest-like distribution surrounding thin-walled vessels; two of them met the malignant diagnostic criteria based on the 5th edition of WHO classification, including marked nuclear atypia and any level of mitotic activity. Immunohistochemistry showed diffusely positive for vimentin (4/4), α-SMA (4/4) and collagen IV (4/4), variably reactive for synaptophysin (3/4) and SSTR2 (2/2), and negative for AE1/AE3 (0/4) and chromogranin A (0/4). Three tested cases harbored no BRAF V600E mutation. Three follow-up cases were alive and free of disease with an average follow-up of 89.3 months. CONCLUSIONS: Tracheal glomus tumors are rare mesenchymal tumors that have overlapping morphologic and immunohistochemical features with neuroendocrine neoplasms. Our cases highlight the importance of careful histomorphological examination and comprehensive immunohistochemical study in reaching a correct diagnosis of glomus tumors of the trachea. Other than BRAF mutation, malignant glomus tumors may have a complex mutational profile.

CARMN-NOTCH2 fusion transcript drives high NOTCH2 expression in glomus tumors of the upper digestive tract.

Glomus tumors (GTs) are perivascular tumors mostly occurring in the distal extremities. Rare cases arise in the digestive tract and may be misdiagnosed with neuroendocrine or gastrointestinal stromal tumors. We aimed to specify the features of GT of the upper digestive tract. Clinical, histological, phenotypic, and molecular features of 16 digestive GTs were analyzed, of whom two underwent whole exome and RNA sequencing to search for gene alterations. RNA-sequencing disclosed a t(1:5)(p13;q32) translocation, which resulted in the fusion of CARMN and NOTCH2 in two GTs. The fusion gene encoded a protein sequence corresponding to the NOTCH2 intracellular domain that functions as transcription factor. These finding was supported by high expression of genes targeted by NOTCH. The CARMN-NOTCH2 translocation was detected in 14 out of 16 (88%) GTs of the upper digestive tract; but in only in two out of six cutaneous GTs (33%). Most digestive GT arose from the stomach (n = 13), and the others from duodenal (2) or oesophagous (1). Nuclear expression of NOTCH2 was detected in the 14 cases containing the fusion transcripts. The CARMN-NOTCH2 fusion transcript may contribute to activation of the NOTCH2 pathway in GT and drive tumor development. The high frequency of this translocation in GT of the upper digestive track suggest that detection of nuclear NOTCH2 expression may be useful diagnostic biomarker of these tumors.

Primary glomus tumour of the pituitary gland: diagnostic challenges of a rare and potentially aggressive neoplasm.

Primary non-neuroendocrine tumours of the pituitary gland and sella are rare lesions often challenging to diagnose. We describe two cases of clinically aggressive primary glomus tumour of the pituitary gland. The lesions occurred in a 63-year-old male and a 30-year-old female who presented with headache, blurred vision and hypopituitarism. Neuroimaging demonstrated large sellar and suprasellar tumours invading the surrounding structures. Histologically, the lesions were characterised by angiocentric sheets and nests of atypical cells that expressed vimentin, smooth muscle actin and CD34. Perivascular deposition of collagen IV was also a feature. Case 2 expressed synaptophysin. INI-1 (SMARCB1) expression was preserved. Both lesions were mitotically active and demonstrated a Ki-67 labelling index of 30%. Next-generation sequencing performed in case 1 showed no mutations in the reading frame of 37 commonly mutated oncogenes, including BRAF and KRAS. Four pituitary glomus tumours have previously been reported, none of which showed features of malignant glomus tumour. Similar to our two patients, three previous examples displayed aggressive behaviour.

A Molecular Reappraisal of Glomus Tumors and Related Pericytic Neoplasms With Emphasis on NOTCH-gene Fusions.

Glomus tumors (GTs), together with myofibroma (MF), myopericytoma (MP), and angioleiomyoma (AL) are classified as members of the perivascular myoid family of tumors. The reported genetic abnormalities across these neoplasms is dissimilar, arguing against a pathogenetically unified family; half of the GT showing NOTCH-gene fusions and a smaller subset BRAF V600E mutations, while PDGFRB mutations are noted in a subset of MF and MP. This study aimed to investigate the prevalence and specificity of NOTCH-gene fusions in a large group of GT and correlate with clinical features. BRAF-VE1 and PDGFRB immunoexpression was also investigated in this cohort. A total of 93 GT and 43 other pericytic lesions (11 MP, 13 MF, and 19 AL) were selected. All cases were tested by fluorescence in situ hybridization for NOTCH1-4 and MIR143 gene abnormalities and 6 cases were investigated by targeted RNA-sequencing. Fluorescence in situ hybridization revealed NOTCH-gene rearrangements in 50 (54%) GT, 2 MP (18%), and 2 AL (11%). NOTCH-rearrangements were present in 34 (68%) benign and 16 (32%) malignant GT. Fusion-positive benign GT were overwhelmingly seen in males with a predilection for extremities, while the malignant GT occurred mostly in viscera. Among the fusion-negative GT, 88% were benign, 9% uncertain malignant potential, and 2% malignant. Half of the fusion-negative GTs occurred in the finger/subungual region. In summary, rearrangements of NOTCH genes are seen in over half of GT, with NOTCH2-MIR143 being the most common fusion (73%), while only a small subset of AL and MP share these abnormalities. The common subungual GT subset lack NOTCH-gene fusions suggesting an alternative pathogenesis. BRAF-VE1 was negative in all 37 cases studied, while strong PDGFRB staining was seen in 14 (21%) cases. Additional studies are needed to investigate the genetic alterations in the fusion-negative cases.

Novel SRF-ICA1L Fusions in Cellular Myoid Neoplasms With Potential For Malignant Behavior.

Pericytic tumors comprise a histologic continuum of neoplasms with perivascular myoid differentiation, which includes glomus tumors, myopericytoma, myofibroma, and angioleiomyoma. Despite their morphologic overlap, recent data suggest a dichotomy in their genetic signatures, including recurrent NOTCH gene fusions in glomus tumors and PDGFRB mutations in myofibromas and myopericytomas. Moreover, SRF-RELA fusions have been described in a subset of cellular variants of myofibroma and myopericytoma showing myogenic differentiation. Triggered by an index case of an unclassified cellular myoid tumor showing a novel SRF-ICA1L fusion we have investigated our files for cases showing similar histology and screened them using a combined approach of targeted RNA sequencing and fluorescence in situ hybridization. A fusion between SRF exon 4 and ICA1L exon 10 or 11 was identified in a total of 4 spindle cell tumors with similar clinicopathologic features. Clinically, the tumors were deep-seated and originated in the trunk or proximal lower extremity of adult patients (age range: 23 to 55 y). Histologically, the tumors were composed of cellular fascicles of monomorphic eosinophilic spindle cells showing increased mitotic activity, harboring densely hyalinized stroma, often with focal areas of necrosis. All 4 tumors had similar immunoprofiles with positivity for smooth muscle actin, calponin, and smooth muscle myosin heavy chain. Tumors were negative for desmin and caldesmon, markers often seen in SRF-RELA-positive tumors with similar morphology. Follow-up information was available in 3 patients. Two patients had no evidence of disease, 2 and 5 years after surgical resection. One patient, a 35-year-old male patient with a 19 cm deep-seated tumor with brisk mitotic activity (>20 mitoses in 10 HPF), developed lung metastases 7 years after initial diagnosis. In summary, we report a series of 4 cellular myoid tumors with novel SRF-ICA1L gene fusions, characterized by bland spindle cell fascicular growth, expression of specific smooth muscle markers, elevated mitotic activity, marked stromal hyalinization, focal coagulative necrosis, and potential for malignant behavior. Given the morphologic overlap with related cellular myopericytic tumors with SRF-RELA fusions, it is likely that SRF-ICA1L fusions define a similar subset of neoplasms composed of immature smooth muscle cells.