PEComa-like Neoplasms Characterized by ASPSCR1-TFE3 Fusion: Another Face of TFE3-related Mesenchymal Neoplasia

A rare case of Alveolar Soft-Part Sarcoma in the Uterine cervix

Alveolar soft-part sarcoma (ASPS), a rare and malignant neoplasm of soft tissues, comprises less than 1% of all soft-tissue sarcomas and is characterized by distinct histopathological and molecular markers. A 27-year-old female presented with a history of postcoital vaginal bleeding and intermittent bleeding over the preceding month. Imaging studies identified abnormal echogenicity and vascular patterns in the posterior cervical lip. Initial histopathological assessment indicated a perivascular epithelioid cell tumor (PEComa) with TFE3 gene rearrangement; however, subsequent immunohistochemical and molecular analyses corroborated the diagnosis of ASPS. The patient underwent a total laparoscopic hysterectomy with bilateral salpingo-oophorectomy. Postoperative pathology revealed that the residual tumor was confined to the inner third of the cervix, with no evidence of lymphovascular or perineural invasion. The patient did not receive adjuvant therapy and was followed for three months postoperatively, during which no recurrence or metastasis was observed. Given the extreme rarity of ASPS, its diagnosis necessitates meticulous scrutiny by pathologists to inform and guide subsequent therapeutic approaches.

TFE3-rearranged ossifying fibromyxoid tumors are uniquely negative for glycoprotein non-metastatic melanoma protein B: A study of 13 TFE3-rearranged mesenchymal tumors

OBJECTIVES

Glycoprotein non-metastatic melanoma protein B (GPNMB) is a transcriptional target of MiTF/TFE3. Prior studies have shown that immunohistochemistry for GPNMB is a sensitive screening tool for renal cell carcinomas with alterations of TSC1/TSC2/MTOR, TFE3, and TFEB genes, as well as alveolar soft part sarcomas (ASPS) and perivascular epithelioid cell neoplasms (PEComas). However, GPNMB expression has not been systematically evaluated in a diverse group of molecularly confirmed, TFE3-rearranged mesenchymal tumors.

METHODS

Our archive was interrogated for TFE3-rearranged non-renal neoplasms previously assessed with our RNA NGS panel. For each case, a whole-slide section was immunostained for GPNMB, and quantified using H-scores. The methylation profiles of the included tumor types were retrieved from our database.

RESULTS

Thirteen TFE3-rearranged tumors were identified, including 6 ossifying fibromyxoid tumors (OFMTs) (PHF1::TFE3), 3 PEComas/PEComa-like neoplasms (ASPSCR1::TFE3, DVL2::TFE3, and PRCC::TFE3, one case each), 2 YAP1::TFE3-rearranged hemangioendotheliomas, one ASPS (ASPSCR1::TFE3), and one unclassified CBX4::TFE3-rearranged sarcoma. Tumors harboring ASPSCR1, PRCC, YAP1, and DVL2 as the fusion partner had a mean H-score of 300, 300, 290 and 280, respectively. All 6 PHF1::TFE3-rearranged OFMTs and the CBX4::TFE3-rearranged sarcoma were GPNMB-negative, despite having similar TFE3 breakpoints to the positive cases (exon 6-7). PHF1::TFE3-rearranged OFMT showed relative hypermethylation of the GPNMB promoter locus cg02203656 compared to ASPS (p = 0.027).

CONCLUSIONS

Although study of additional cases is necessary, these findings suggest that the downstream effects of TFE3-rearrangement are different in PHF1::TFE3-rearranged OFMTs, compared to other known TFE3-rearranged neoplasms. TFE3-rearranged OFMTs are epigenetically distinct, implying that the impact of TFE3-rearrangement may be lineage-dependent.

YAP1::TFE3 fusion in a case of malignant TFE3-rearranged PEComa of the lung: expanding the spectrum of pulmonary PEComa-like mesenchymal neoplasms

The family of PEComa encompasses a heterogeneous group of related mesenchymal neoplasms with myomelanocytic differentiation, a distinctive subset of which is characterized by TFE3 gene rearrangement. Recurrent YAP1::TFE3 fusion has been found in clear cell stromal tumor of the lung (CCST-L), and most recently, in two cases classified as inflammatory spindle cell PEComa. However, the potential relationship between CCST-L and PEComa remains unclear. Herein, we report a case of primary pulmonary malignant TFE3-rearranged PEComa with prototypical morphological and immunohistochemical features, unexpectedly harboring YAP1::TFE3 fusion. Our findings further expanded the morphological and molecular spectrum of PEComa-like mesenchymal neoplasms of the lung.

TFE3 -rearranged Head and Neck Neoplasms : Twenty-two Cases Spanning the Morphologic Continuum Between Alveolar Soft Part Sarcoma and PEComa and Highlighting Genotypic Diversity

TFE3 rearrangements characterize histogenetically, topographically, and biologically diverse neoplasms. Besides being a universal defining feature in alveolar soft part sarcoma (ASPS) and clear cell stromal tumor of the lung, TFE3 fusions have been reported in subsets of renal cell carcinoma, perivascular epithelioid cell tumor (PEComa), epithelioid hemangioendothelioma and ossifying fibromyxoid tumors. TFE3 -related neoplasms are rare in the head and neck and may pose diagnostic challenges. We herein describe 22 TFE3 fusion neoplasms affecting 11 males and 11 females aged 4 to 79 years (median, 25) and involving different head and neck sites: sinonasal cavities (n = 8), tongue (n = 4), oral cavity/oropharynx (n = 3), salivary glands (n = 2), orbit (n = 2), and soft tissue or unspecified sites (n = 3). Based on morphology and myomelanocytic immunophenotype, 10 tumors qualified as ASPS, 7 as PEComas (3 melanotic; all sinonasal), and 5 showed intermediate (indeterminate) histology overlapping with ASPS and PEComa. Immunohistochemistry for TFE3 was homogeneously strongly positive in all cases. Targeted RNA sequencing/FISH testing confirmed TFE3 fusions in 14 of 16 successfully tested cases (88%). ASPSCR1 was the most frequent fusion partner in ASPS (4 of 5 cases); one ASPS had a rare VCP::TFE3 fusion. The 6 successfully tested PEComas had known fusion partners as reported in renal cell carcinoma and PEComas ( NONO, PRCC, SFPQ , and PSPC1 ). The indeterminate tumors harbored ASPSCR1::TFE3 (n = 2) and U2AF2::TFE3 (n = 1) fusions, respectively. This large series devoted to TFE3-positive head and neck tumors illustrates the recently proposed morphologic overlap in the spectrum of TFE3 -associated mesenchymal neoplasms. While all PEComas were sinonasal, ASPS was never sinonasal and occurred in diverse head and neck sites with a predilection for the tongue. The indeterminate (PEComa-like) category is molecularly more akin to ASPS but shows different age, sex, and anatomic distribution compared with classic ASPS. We report VCP as a novel fusion partner in ASPS and PSPC1 as a novel TFE3 fusion partner in PEComa (detected in one PEComa). Future studies should shed light on the most appropriate terminological subtyping of these highly overlapping tumors.

Inflammatory spindle cell PEComa of the lung with YAP1::TFE3 fusion: a report of two cases and a potential relationship with clear cell stromal tumour

AIMS

The PEComa family of tumours is defined by spindle/epithelioid cells with myomelanocytic differentiation. A small subset harbours TFE3 fusion; however, YAP1::TEE3 has not been reported. Clear cell stromal tumour of the lung (CCST-L) is an emerging entity characterized by spindle to epithelioid cells with focal cytoplasmic clearing, inflammatory infiltrates, no myomelanocytic differentiation, and YAP1::TFE3 fusion. Herein, we report two cases of lung tumours with myomelanocytic differentiation that showed inflammatory spindle cell histology, focal epithelioid clear cells, as well as YAP1::TFE3 fusion.

METHODS AND RESULTS

The patients were both men, aged 61 and 68 years. The tumours in both cases presented as well-circumscribed solid masses involving the lung hilum. After lobectomy, no recurrence was observed at 7 and 32 months. Both tumours shared storiform to short fascicular growth of long spindle cells, with a minor component of epithelioid cells showing clear cytoplasm in the background of substantial intratumoral chronic inflammation and dilated blood vessels. One tumour showed focal melanin deposition. Both tumours were immunohistochemically positive for HMB45, Melan A, and h-caldesmon. Fluorescence in situ hybridization assays indicated the presence of YAP1::TFE3 fusions, which was confirmed by RNA sequencing in one case tested, and by immunohistochemical TFE3 expression and loss of YAP1 C-terminus staining.

CONCLUSION

We present two cases of inflammatory spindle to epithelioid cell tumours of the lungs with myomelanocytic differentiation and YAP1::TFE3 fusion. This unique morphology and gene fusion suggest that these tumours may constitute a distinct subset of lung PEComa. Furthermore, morphological and molecular overlap with CCST-L gives rise to a hypothesis of a potential inherent relationship between PEComa and CCST-L.

The Spectrum of Fusions Occurring in Non-Smooth Muscle Mesenchymal Uterine Tumors: A Review of the Current Knowledge

CONTEXT.—

Non-smooth muscle uterine sarcomas are mostly represented by low-grade endometrial stromal sarcoma. However, several other rare, distinct types of uterine sarcoma are recognized, including high-grade endometrial stromal sarcoma, tumors with kinase fusions, uterine tumors resembling ovarian sex cord tumors, soft tissue-type sarcoma, and emerging entities such as KAT6A/B-rearranged tumors. The landscape of uterine sarcomas has changed, mostly because of the increasing knowledge concerning their molecular aberrations.

OBJECTIVE.—

To offer a comprehensive review of the literature focusing on fusions occurring in tumors other than smooth muscle mesenchymal uterine tumors with respect to their type, frequency, and overlap between diagnostic categories and entities.

DATA SOURCES.—

The data were mined from the PubMed/MEDLINE database covering the time period from January 1988 to June 2023. In total, 156 studies focusing on the problematics of fusions occurring in non-smooth muscle mesenchymal uterine tumors were selected, and thus became the basis for this review.

CONCLUSIONS.—

One hundred ten fusions were identified in 703 tumors. The diagnostic significance of the molecular aberrations occurring in these tumors can be unclear in some cases. This can be related to the rare aberrations with a limited number of reported cases. Additionally, even well-known aberrations considered as specific for a certain distinct entity can occur in other lesions, the biological behavior and clinical significance of which can differ substantially.

[Translocation-associated uterine mesenchymal tumors: The new without forgetting the old. An integrated diagnostic approach]

This review focuses on uterine mesenchymal tumors that are defined on a molecular level by a single and unique genetic alteration, that is somehow necessary and sufficient to allow tumor growth and progression. Although diverse from a clinical, morphological and immunohistochemical point of view, the different entities we are going to talk about share both a simple genomic profile with a low number of chromosomal alterations observed by CGH Array (few deletions, gains or amplifications...) and a low mutational burden observed by sequencing technics. Some of these entities are already well known and described in the literature when found outside of the uterus and gynecological tract. It remains intriguing that uterine mesenchymal pathology has been lagging behind when compared to its extrauterine counterpart. How can we explain that when it comes to inflammatory myofibroblastic tumors, abundant numbers of articles have been published since the 70's, but it was only in the early 2000s that the first relevant descriptions of this tumor in the uterus emerged? Certainly, the increased accuracy, availability, and use of molecular biology technics and in particular RNA sequencing in the area of uterine pathology can partly explain the reduction of the gap between soft tissue and uterine pathology we currently observe. Other reasons explaining this gap may be the high prevalence of smooth muscle tumors in the uterus and the abounding diversity of their morphological aspects, which may have partly eclipsed the array of differential diagnoses. Last but not least, one can hypothesize that the relative "simplicity" of hysterectomy procedures, referring to their safety and accessibility, has cured most of the lesions and partly clouded our knowledge regarding the biological potential and natural history of these newly described entities. As a consequence of this situation, our reader will often encounter the wording "uncertain malignant potential", as for some of these rare entities, evidence to establish reliable prognostic variables is still insufficient. We hope this review to be a useful tool to guide pathologists through the diversity and complexity of uterine mesenchymal tumors. As a scientific and medical community, sharing this knowledge will help us to collectively raise our vigilance and awareness by expanding the array of our differential diagnoses. We hope this will lead to more cases being accurately diagnosed, and ultimately, to a deeper knowledge regarding the biological potential and clinical evolution of these tumors. From a therapeutical point of view, the consequences of an accurate diagnosis for the patient are already appreciable through the use of targeted therapy. Examples include: ALK inhibitors in inflammatory myofibroblastic tumor, tyrosine-kinase inhibitors in COL1A::PDGFB rearranged sarcomas or mTOR inhibitors in PEComa.

TFE3-Rearranged Tumors of the Kidney: An Emerging Conundrum

Background: Identical translocations involving the TFE3 gene and various partners have been found in both renal and soft tissue tumors, like alveolar soft part sarcoma (ASPSCR1), ossifying fibromyxoid tumor (PHF1), epithelioid hemangioendothelioma, and the clear cell stromal tumor of the lung (YAP1). Methods: Herein, we review in detail the clinicopathologic and molecular data of TFE3-rearranged renal tumors and propose our perspective, which may shed light on this emerging conundrum. Results: Among the kidney tumors carrying TFE3 translocations, most are morphologically heterogeneous carcinomas labeling for the tubular marker PAX8. The others are mesenchymal neoplasms known as PEComas, characterized by epithelioid cells co-expressing smooth muscle actin, cathepsin-K, melanogenesis markers, and sometimes melanin pigment deposition. Over the past 30 years, numerous TFE3 fusion partners have been identified, with ASPL/ASPSCR1, PRCC, SFPQ/PSF, and NONO being the most frequent. Conclusions: It is not well understood why similar gene fusions can give rise to renal tumors with different morpho-immunophenotypes, which may contribute to the recent disagreement regarding their classification. However, as these two entities, respectively, epithelial and mesenchymal in nature, are widely recognized by the pathology community and their clinicopathologic features well established, we overall believe it is still better to retain the names TFE3-rearranged renal cell carcinoma and TFE3-rearranged PEComa.

Alveolar soft part sarcomas in young patients: The French national NETSARC+ network experience

BACKGROUND AND AIMS

Alveolar soft part sarcoma (ASPS) is an ultra-rare chemo-resistant sarcoma in children, occurring preferentially in young adults. We aimed to describe and compare its clinical presentation and behaviour in children and young adults to determine whether the same therapeutic strategy should be addressed for both populations.

METHODS

National retrospective multicentre study of children (0-18 years) vs. young adults (19-30 years) included in the "ConticaBase" sarcoma database, treated for ASPS between 2010 and 2019 with pathology reviewed via the NETSARC + network.

RESULTS

Overall, 45 patients were identified, 19 children (42%) and 26 young adults (58%). All ASPS diagnoses were confirmed with TFE3 rearrangement by immunohistochemistry or FISH. All clinical characteristics were balanced between both populations with frequent metastases at diagnosis (8/19 vs. 10/26). The therapeutic strategy was based on surgery (17/19 vs. 21/26), radiotherapy (8/19 vs. 12/26) ± systemic treatment (8/19 vs. 9/26). In patients with initially localized disease, metastatic relapse occurred only in adults (8/16), whereas metastatic progression was present in both metastatic groups (5/8 vs. 8/10). After a median follow-up of 5.2 years (range, 0.2-12.2), 5-year EFS was 74% [95%CI, 56-96] vs. 47% [30-74] (p = 0.071) respectively, and 5-year OS was 95% [85-100] vs. 85% [70-100] (p = 0.84). For localized tumours, 5-year MFS was 100% [100-100] vs. 60% [39-91] (p = 0.005). The 5-year OS of all patients with metastasis at diagnosis was 80.2% (62.2%-100%).

CONCLUSIONS

ASPS appears to have the overall same clinical characteristics, but a more aggressive behaviour in young adults than in children. However, despite frequent metastases at diagnosis, long-term survival is high in both groups. Overall, the same therapeutic strategies may be considered for both populations.

Renal epithelioid angiomyolipomas overexpress TFE3 and the TFE3-regulated gene TRIM63 in the absence of TFE3 rearrangement

Angiomyolipoma (AML) is a neoplasm within the perivascular epithelioid cell tumor family that occurs somewhat frequently in the kidney. Most are indolent and discovered incidentally, with rare tumors demonstrating malignant clinical behavior. A small subset of renal AMLs with epithelioid features are associated with aggressive behavior, and may demonstrate morphologic overlap with renal cell carcinomas (e.g., clear cell renal cell carcinoma (RCC), TFE3-rearranged RCC). Prior studies of spindle cell and epithelioid AMLs have identified rare examples with underlying TFE3 gene fusions. TFE3 protein expression (demonstrated by immunohistochemistry) with no evidence of concurrent TFE3 rearrangements has been reported previously in 4/24 AMLs (17%) (Argani et al. Am J Surg Pathol 34:1395-1406, 2010). Currently, the relationship between TFE3 protein expression, TFE3 fusions, and expression of TFE3-mediated genes remains incompletely understood in renal epithelioid AMLs. We sought to explore these relationships using TFE3 break-apart fluorescence in situ hybridization (FISH) and TRIM63 RNA in situ hybridization (ISH) on epithelioid AMLs with moderate to strong TFE3 expression by immunohistochemistry. RNA sequencing (fusion panel) was performed on two cases with negative FISH results to assess for FISH-cryptic gene fusions. The series comprised five epithelioid AMLs from four patients (three women, one man) aged 13 to 76 years. All were considered positive for TFE3 by immunohistochemistry (2 + /3 + expression). TRIM63 ISH was performed on four specimens from three patients, yielding positive results in 3/3 tumors (100%) that were successfully analyzed. TFE3 break-apart FISH was performed on all samples, demonstrating a TFE3 rearrangement in only 1/4 tumors (25%). RNA sequencing demonstrated the absence of productive TFE3 gene fusions in three tumors with negative break-apart TFE3 FISH results. This study demonstrates that renal epithelioid AMLs overexpress TFE3 and TFE3-mediated genes (TRIM63) even in the absence of TFE3 rearrangements. This finding could be explained by functional upregulation of TFE3 secondary to activation of the mammalian target of rapamycin complex 1 (mTORC1). Expression of TFE3 and TRIM63 in this tumor type represents a potential pitfall, given the morphologic and immunophenotypic overlap between epithelioid AML and TFE3-altered renal cell carcinoma.

TFE3 -Rearranged PEComa/PEComa-like Neoplasms : Report of 25 New Cases Expanding the Clinicopathologic Spectrum and Highlighting its Association With Prior Exposure to Chemotherapy

Since their original description as a distinctive neoplastic entity, ~50 TFE3 -rearranged perivascular epithelioid cell tumors (PEComas) have been reported. We herein report 25 new TFE3 -rearranged PEComas and review the published literature to further investigate their clinicopathologic spectrum. Notably, 5 of the 25 cases were associated with a prior history of chemotherapy treatment for cancer. This is in keeping with prior reports, based mainly on small case series, with overall 11% of TFE3 -rearranged PEComas being diagnosed postchemotherapy. The median age of our cohort was 38 years. Most neoplasms demonstrated characteristic features such as nested architecture, epithelioid cytology, HMB45 positive, and muscle marker negative immunophenotype. SFPQ was the most common TFE3 fusion partner present in half of the cases, followed by ASPSCR1 and NONO genes. Four of 7 cases in our cohort with meaningful follow-up presented with or developed systemic metastasis, while over half of the reported cases either recurred locally, metastasized, or caused patient death. Follow-up for the remaining cases was limited (median 18.5 months), suggesting that the prognosis may be worse. Size, mitotic activity, and necrosis were correlated with aggressive behavior. There is little evidence that treatment with MTOR inhibitors, which are beneficial against TSC -mutated PEComas, is effective against TFE3 -rearranged PEComas: only one of 6 reported cases demonstrated disease stabilization. As co-expression of melanocytic and muscle markers, a hallmark of conventional TSC -mutated PEComa is uncommon in the spectrum of TFE3 -rearranged PEComa, an alternative terminology may be more appropriate, such as " TFE3 -rearranged PEComa-like neoplasms," highlighting their distinctive morphologic features and therapeutic implications.

An unusual case of primary splenic soft part alveolar sarcoma: case report and review of the literature with emphasis on the spectrum of TFE3-associated neoplasms

BACKGROUND

Alveolar soft part sarcoma is a rare tumour of soft tissues, mostly localized in muscles or deep soft tissues of the extremities. In rare occasions, this tumour develops in deep tissues of the abdomen or pelvis.

CASE PRESENTATION

In this case report, we described the case of a 46 year old man who developed a primary splenic alveolar soft part sarcoma. The tumour displayed typical morphological alveolar aspect, as well as immunohistochemical profile notably TFE3 nuclear staining. Detection of ASPSCR1 Exon 7::TFE3 Exon 6 fusion transcript in molecular biology and TFE3 rearrangement in FISH confirmed the diagnosis.

CONCLUSION

We described the first case of primary splenic alveolar soft part sarcoma, which questions once again the cell of origin of this rare tumour.

Soft Tissue Perivascular Epithelioid Cell Tumors

Perivascular epithelioid cell tumors (PEComas) are a heterogenous group of mesenchymal neoplasms with a mixed myomelanocytic immunophenotype. PEComa-family tumors include angiomyolipoma, lymphangioleiomyomatosis, and a large category of rare neoplasms throughout the body that are now classified under the umbrella term "PEComa." This review focuses on recent advances in the clinicopathological and molecular features of PEComas, with an emphasis on PEComas that originate in soft tissue.

Evaluation of TRIM63 RNA in situ hybridization (RNA-ISH) as a potential biomarker for alveolar soft-part sarcoma (ASPS)

Alveolar soft-part sarcoma (ASPS) is a rare soft tissue tumor with a broad morphologic differential diagnosis. While histology and immunohistochemistry can be suggestive, diagnosis often requires exclusion of other entities followed by confirmatory molecular analysis for its characteristic ASPSCR1-TFE3 fusion. Current stain-based biomarkers (such as immunohistochemistry for cathepsin K and TFE3) show relatively high sensitivity but may lack specificity, often showing staining in multiple other entities under diagnostic consideration. Given the discovery of RNA in situ hybridization (RNA-ISH) for TRIM63 as a sensitive and specific marker of MiTF-family aberration renal cell carcinomas, we sought to evaluate its utility in the workup of ASPS. TRIM63 RNA-ISH demonstrated high levels (H-score greater than 200) of expression in 19/20 (95%) cases of ASPS (average H-score 330) and was weak or negative in cases of paraganglioma, clear cell sarcoma, rhabdomyosarcoma, malignant epithelioid hemangioendothelioma, as well as hepatocellular and adrenal cortical carcinomas. Staining was also identified in tumors with known subsets characterized by TFE3 alterations such as perivascular epithelioid cell neoplasm (PEComa, average H-score 228), while tumors known to exhibit overexpression of TFE3 protein without cytogenetic alterations, such as melanoma and granular cell tumor, generally showed less TRIM63 ISH staining (average H-scores 147 and 96, respectively). Quantitative assessment of TRIM63 staining by RNA-ISH is potentially a helpful biomarker for tumors with molecular TFE3 alterations such as ASPS.

Comparative genomics incorporating translocation renal cell carcinoma mouse model reveals molecular mechanisms of tumorigenesis

Translocation renal cell carcinoma (tRCC) most commonly involves an ASPSCR1-TFE3 fusion, but molecular mechanisms remain elusive and animal models are lacking. Here, we show that human ASPSCR1-TFE3 driven by Pax8-Cre (a credentialed clear cell RCC driver) disrupted nephrogenesis and glomerular development, causing neonatal death, while the clear cell RCC failed driver, Sglt2-Cre, induced aggressive tRCC (as well as alveolar soft part sarcoma) with complete penetrance and short latency. However, in both contexts, ASPSCR1-TFE3 led to characteristic morphological cellular changes, loss of epithelial markers, and an epithelial-mesenchymal transition. Electron microscopy of tRCC tumors showed lysosome expansion, and functional studies revealed simultaneous activation of autophagy and mTORC1 pathways. Comparative genomic analyses encompassing an institutional human tRCC cohort (including a hitherto unreported SFPQ-TFEB fusion) and a variety of tumorgraft models (ASPSCR1-TFE3, PRCC-TFE3, SFPQ-TFE3, RBM10-TFE3, and MALAT1-TFEB) disclosed significant convergence in canonical pathways (cell cycle, lysosome, and mTORC1) and less established pathways such as Myc, E2F, and inflammation (IL-6/JAK/STAT3, interferon-γ, TLR signaling, systemic lupus, etc.). Therapeutic trials (adjusted for human drug exposures) showed antitumor activity of cabozantinib. Overall, this study provides insight into MiT/TFE-driven tumorigenesis, including the cell of origin, and characterizes diverse mouse models available for research.

PEComa with ASPSCR1::TFE3 fusion: expanding the molecular genetic spectrum of TFE3-rearranged PEComa with an emphasis on overlap with alveolar soft part sarcoma

AIMS

Mesenchymal neoplasms involving TFE3 gene fusions are diverse, mainly include alveolar soft part sarcoma (ASPS) that is characterised by ASPSCR1::TFE3 fusion, and a small subset of perivascular epithelioid cell tumours (PEComas) referred to as TFE3-rearranged PEComa, that most frequently harbours SFPQ::TFE3 fusion. Historically, ASPS and TFE3-rearranged PEComa are considered two distinctive entities despite their known morphological overlap. However, recent studies have suggested a potential histogenetic relationship between them, and several neoplasms that showed morphological features more closely fit PEComa rather than ASPS but harboured ASPSCR1::TFE3 fusion have been documented. In this study, we report three cases of PEComa with ASPSCR1::TFE3 fusion.

METHODS AND RESULTS

Clinicopathological features were assessed and partner agnostic targeted next-generation sequencing on clinically validated platforms were performed. The patients are two females and one male with age at presentation ranging from 21 to 51 years. All three tumours were located in the viscera (rectum, kidney and cervix). On a relatively limited follow-up period (range = 9-15 months), all patients are alive without evidence of recurrent or metastatic disease. The neoplasms were composed of tight nested architecture of epithelioid clear cells separated by a delicate vascular network, two of which were associated with sheets of plump spindle cells, and none showed significant discohesive tumour morphology. Immunohistochemically, in addition to TFE3 protein, all three neoplasms demonstrated co-expression of melan-A and smooth muscle actin. RNA-sequencing identified ASPSCR1::TFE3 fusion in all three cases that were confirmed by subsequent fluorescence in-situ hybridisation analyses.

CONCLUSIONS

Our study expands the molecular genetic spectrum of TFE3-rearranged PEComa and further indicates its close relationship to ASPS.

PEComa of the Adrenal Gland: A Clinicopathologic Series of 7 Cases

PEComas are a family of mesenchymal neoplasms composed of histologically distinctive perivascular epithelioid cells which demonstrate myomelanocytic differentiation. PEComas of the adrenal gland are very rare and can represent a considerable diagnostic challenge given their morphologic overlap with more common adrenal cortical neoplasms. We present the clinicopathologic features of 7 primary adrenal PEComas. The cohort comprised 5 male and 2 female patients with a median age of 63 years (range: 31 to 71 y). One patient had Birt-Hogg-Dubé syndrome and another had Lynch syndrome; however, none had a history of tuberous sclerosis complex. Histologically, tumors showed nested and/or sheet-like growth and epithelioid cytomorphology with pale-to-eosinophilic granular cytoplasm. Two tumors had an admixed spindle cell component. There was a median of 4 mitoses per 10 HPFs (range: 0 to 8). Necrosis was present in 4 tumors and lymphovascular invasion in 1. Four tumors were classified as malignant. By immunohistochemistry, tumors were positive for HMB-45 (3/7), MITF (3/3), Melan-A (3/7), smooth muscle actin (5/7), desmin (5/7), and caldesmon (1/1). Two tumors were positive for TFE3 (2/4). Inhibin and SF1 were negative in all tumors assessed (0/6). Of 3 patients with available clinical follow-up information, 1 patient developed locally recurrent and metastatic disease (at 18 mo) and was alive with persistent disease at the last follow-up. Two patients had no recurrent or metastatic disease at the last follow-up (60 and 25 mo). Although PEComas of the adrenal gland are rare, pathologists need to be alert to this entity in the differential diagnosis of primary adrenocortical neoplasms. In suspected cases, the judicious use of melanocytic and smooth muscle markers, in addition to TFE3 and markers of adrenocortical differentiation (such as SF1 and inhibin) can assist in diagnosis. As in PEComas arising at other visceral sites, an association with tuberous sclerosis complex seems to be uncommon.