PEComas of the kidney and of the genitourinary tract

TFE3-rearranged nonmelanotic renal PEComa: a case series expanding their phenotypic and fusion landscape

AIMS

A subset of exceptionally rare primary renal perivascular epithelioid cell tumours (PEComas) that harbour Xp11.2 translocation have been reported, but no larger series devoted to this topic have been published.

METHODS AND RESULTS

We describe the clinicopathological and molecular features of 10 renal PEComas, collected from our routine and consultation files. There were five female and five male patients aged 14-65 (median: 32 years). One patient had a history of childhood neuroblastoma, but no patients were known to have a tuberous sclerosis complex or other hereditary disorder. Complete surgical excision was the treatment for all patients. The available follow-up in five patients indicated a favourable outcome in 4/5 cases. Tumour size ranged from 2.8 to 15.2 cm (median, 5.2 cm). Immunohistochemistry revealed consistently strong TFE3 expression in all tumours, whereas PAX8 and keratin cocktails were uniformly negative. Other positive markers included HMB45 (7/9 tumours), CathepsinK (7/9 tumours), and CD117 (KIT) (3/5 tumours). TFE3 rearrangements were detected in 8/9 tumours (by targeted RNA sequencing in seven and by FISH in one). The identified fusion partners included SFPQ (n = 2) and one tumour each with ASPSCR1, ZC3H4, MED15, RBMX, and PRCC. One tumour that lacked TFE3 rearrangement by next-generation sequencing (NGS) and fluorescence in situ hybridization (FISH) revealed a large intrachromosomal deletion involving PKD1 and TSC2 by DNA-based NGS.

CONCLUSION

This study highlights the morphologic and genetic diversity of TFE3-rearranged primary renal PEComas and underlines the value of surrogate TFE3 immunohistochemistry in identifying them. The lack of PAX8 and keratin expression represents the mainstay for distinguishing these tumours from MiTF-associated renal cell carcinomas. In addition, we report rare (ZC3H4, RBMX) and novel (MED15) TFE3 fusion partners in PEComa.

Comprehensive Insights Into Renal Perivascular Epithelioid Cell Neoplasms: From Molecular Mechanisms to Clinical Practice

Perivascular epithelioid cell neoplasms (PEComas) are a rare category of mesenchymal tissue tumors, manifesting across various tissues and organs such as the kidneys, liver, lungs, pancreas, uterus, ovaries, and gastrointestinal tract. They predominantly affect females more than males. PEComas characteristically express both melanocytic and smooth muscle markers, making immunohistochemistry vital for their diagnosis. Renal angiomyolipoma (AML) represents a common variant of PEComas, typically marked by favorable prognoses. Nonetheless, only a small fraction of subtypes, especially epithelioid AML, possess the capacity to be malignant. Renal PEComas usually appear as asymptomatic masses accompanied by vague imaging characteristics. The main methods for diagnosis are histopathological analysis and the application of immunohistochemical stains. Presently, a uniform treatment plan for renal PEComas is absent. Strategies for management include active surveillance, selective arterial embolization, surgical procedures, and drug-based treatments. The focus of this review is on renal PEComas, shedding light on their pathogenesis, pathological characteristics, clinical presentations, diagnosis, and treatment modalities, and incorporating a clinical case study.

Comprehensive proteogenomic characterization of rare kidney tumors

Non-clear cell renal cell carcinomas (non-ccRCCs) encompass diverse malignant and benign tumors. Refinement of differential diagnosis biomarkers, markers for early prognosis of aggressive disease, and therapeutic targets to complement immunotherapy are current clinical needs. Multi-omics analyses of 48 non-ccRCCs compared with 103 ccRCCs reveal proteogenomic, phosphorylation, glycosylation, and metabolic aberrations in RCC subtypes. RCCs with high genome instability display overexpression of IGF2BP3 and PYCR1. Integration of single-cell and bulk transcriptome data predicts diverse cell-of-origin and clarifies RCC subtype-specific proteogenomic signatures. Expression of biomarkers MAPRE3, ADGRF5, and GPNMB differentiates renal oncocytoma from chromophobe RCC, and PIGR and SOSTDC1 distinguish papillary RCC from MTSCC. This study expands our knowledge of proteogenomic signatures, biomarkers, and potential therapeutic targets in non-ccRCC.

mTOR eosinophilic renal cell carcinoma: a distinctive tumor characterized by mTOR mutation, loss of chromosome 1, cathepsin-K expression, and response to target therapy

In the spectrum of oncocytic renal neoplasms, a subset of tumors with high-grade-appearing histologic features harboring pathogenic mutations in mammalian target of rapamycin (mTOR) and hitherto clinical indolent behavior has been described. Three cases (2F,1 M) with histologically documented metastases (lymph node, skull, and liver) were retrieved and extensively investigated by immunohistochemistry, FISH, and next-generation sequencing. Tumors were composed of eosinophilic cells with prominent nucleoli (G3 by ISUP/WHO) arranged in solid to nested architecture. Additionally, there were larger cells with perinuclear cytoplasmic shrinkage and sparse basophilic Nissl-like granules, superficially resembling the so-called spider cells of cardiac rhabdomyomas. The renal tumors, including the skull and liver metastases, showed immunoexpression PAX8, CK8-18, and cathepsin-K, and negativity for vimentin. NGS identified mTOR genetic alterations in the three cases, including the skull and liver metastases. One patient was then treated with Everolimus (mTOR inhibitors) with clinical response (metastatic tumor shrinkage). We present a distinct renal tumor characterized by high-grade eosinophilic cells, cathepsin-K immunohistochemical expression, and harboring mTOR gene mutations demonstrating a malignant potential and showing responsiveness to mTOR inhibitors.

Molecular Characterization of Malignant Renal Epithelioid Angiomyolipoma: A Review of Two Cases

OBJECTIVES

Epithelioid angiomyolipoma (EAML, perivascular epithelioid cell tumor) is an uncommon primary renal tumor that may recur or metastasize, although there remain limited data for prediction of these outcomes. Here, we report two cases of renal EAML with molecular testing, adding to the existing literature of potential alterations associated with malignant behavior.

METHODS

Tumors diagnosed as malignant renal EAML were identified, and clinical data, radiology, histology, immunohistochemistry, and molecular testing results were reviewed.

RESULTS

Two cases of malignant renal EAML were identified, both of which demonstrated TSC2 and TP53 mutations. In ATRX, one had a mutation and the other had a variant of uncertain significance. In addition, one patient had a synchronous classic angiomyolipoma that lacked TP53 and ATRX alterations.

CONCLUSIONS

These findings highlight the molecular landscape of malignant renal EAML and expand on the existing literature suggesting a role for TP53 and ATRX alterations in malignant progression of these tumors. The presence of synchronous benign and malignant tumors within the same patient offers a unique opportunity to directly compare the molecular alterations, further supporting the association with aggressive behavior.

Transurethral en bloc resection of a bladder perivascular epithelioid cell tumor (PEComa): a case report

BACKGROUND

Perivascular epithelioid cell tumor (PEComa) is a mesenchymal tumor with distinct histologic and immunologic features. PEComas that originate in the bladder are extremely rare clinically, with only 35 cases reported in the English literature thus far. Here, we report a case of bladder PEComa resection by transurethral en bloc resection of bladder tumor (ERBT).

CASE PRESENTATION

A 66-year-old female with a history of poorly controlled type 2 diabetes with associated complications of frequent urinary tract infections presented to our hospital for a routine physical examination. Outpatient ultrasound examination revealed a strong echogenic mass of approximately 1.5 × 1.3 × 1.3 cm in size on the posterior wall of the bladder. The enhanced computed tomography and enhanced magnetic resonance imaging after admission both suggested a well-defined isolated nodular mass on the posterior wall of the bladder with significant enhancement on the enhanced scan. The tumor was successfully and completely resected by ERBT. Postoperative pathological examination and immunohistochemical results confirmed the mass was a bladder PEComa. No tumor recurrence was observed in the six-month postoperative follow-up.

CONCLUSION

Bladder PEComa is an extremely rare mesenchymal tumor of the urinary system. When imaging and cystoscopy reveal a nodular mass with an abundant blood supply in the bladder, PEComa should be included in the differential diagnosis of bladder tumors. Surgical resection is currently the primary option for the treatment of bladder PEComa. For a solitary, pedunculated, narrow-based, small-sized bladder PEComa, resection of the tumor by ERBT was a safe and feasible approach in our patient and may be considered for similar cases in the future.

Cytomorphology of renal angiomyolipoma: performance and accuracy of touch preparation of core needle biopsy

INTRODUCTION

The recognition of renal angiomyolipoma (AML) can be challenging based on cytology preparations such as touch preparation (TP) of core needle biopsy (CNB) and fine needle aspiration. This study evaluated the cytologic features and performance of TP of CNB during rapid onsite evaluation (ROSE) of renal AML.

MATERIALS AND METHODS

A pathology database search was performed between 2000 and 2021 for renal CNB specimens with ROSE using TP that were primarily favored AML on preliminary impression and/or confirmed AML on CNB or subsequent resection.

RESULTS

Twenty confirmed AML were identified (90% female, median age 65.5 years). Sixteen (80%) were deemed adequate for diagnosis at the time of ROSE, and 9 of 16 (56%) had available onsite impression: AML was favored in 4 of 9 cases (44%). Examination of TP slides revealed spindle/epithelioid cells in 20 (100%), adipose tissue in 14 (70%), and blood vessels in 3 (15%). All AML cases were subsequently confirmed by immunohistochemistry. Additionally, 3 other cases with ROSE favoring AML revealed to be "renal parenchyma with fibrosis," clear cell papillary renal cell tumor and clear cell renal cell carcinoma.

CONCLUSIONS

Onsite evaluation of TP ensures adequate material for diagnosis in most renal AML. Spindle/epithelioid cells were the most common component seen on TP, followed by adipose tissue. Blood vessels were rarely seen. While the recognition of AML at ROSE can be challenging, proper evaluation is important in obtaining adequate diagnostic tissue. Correlation with CNB and utilization of immunohistochemistry are crucial for arriving at the diagnosis.

Case report: Kidney perivascular epithelioid cell tumor treated with anti-VEGFR tyrosine kinase inhibitor and MTOR inhibitor

Perivascular epithelioid cell tumors (PEComas) are rare mesenchymal tumors arising from perivascular epithelial cells. There was no standard treatment for unresectable PEComa before 2021. For a low incidence and a rarely curable disease, development of new therapy is essential. A 45-year-old female was diagnosed with malignant renal PEComa (likely with TFE3 rearrangement) that underwent rapid progression after 10 months of surgery. The patient then received the tyrosine kinase inhibitor (TKI) Apatinib, and the tumor remained stable for 15 months before another progression. The patient then received the MTOR inhibitor everolimus that alleviated her symptoms but the tumor went into remission again after another 15 months. This result suggests that antagonizing the vascular endothelial growth factor receptor (VEGFR) pathway be a useful strategy for malignant PEComas, along with the MTOR pathway inhibition that had recently been approved for the rare tumor.

TSC loss is a clonal event in eosinophilic solid and cystic renal cell carcinoma: a multiregional tumor sampling study

Eosinophilic, solid and cystic (ESC) renal cell carcinoma (RCC) is characterized by a solid and cystic architecture with cells showing abundant eosinophilic cytoplasm with hobnail arrangement and a cytokeratin 7-negative/cytokeratin 20-positive immunophenotype. Recent studies have suggested that bi-allelic events affecting TSC genes might play an important role for such tumors. However, only indirect evidence of the clonal origin of TSC mutation has been gathered so far. Therefore, in this paper we aimed to perform multi-regional tumor sampling molecular analysis in four ESC RCC cases that had been completely embedded, three sporadic and one occurring in a patient with tuberous sclerosis complex (TSC). Histologically, the 4 cases showed cystic and solid architecture and cells with abundant eosinophilic cytoplasm with cytoplasmic stippling and round to oval nuclei. Immunohistochemistry showed at least focal expression of cytokeratin 20 in all tissue samples and negative cytokeratin 7, as well as diffuse positivity for S100A1 and at least focal expression of cathepsin K in three out of four cases. The sporadic cases showed the same somatic TSC1 mutations in all tissue samples analyzed, while the TSC-associated case showed the same TSC1 alteration in both normal tissue and all tumor samples analyzed, proving the germline nature of the alteration. In conclusion, our data demonstrate that clonal TSC loss is a key event in ESC RCC and support considering ESC RCC as an entity given its distinct morphologic, immunophenotypical and molecular characteristics.

Mesenchymal Neoplasms of the Prostate and Seminal Vesicles: Spectrum of Disease with Radiologic-Pathologic Correlation

There is a wide spectrum of benign and malignant mesenchymal neoplasms of the prostate, which account for less than 1% of all prostatic tumors. These include distinctive tumors that arise from the specialized prostatic stroma and site-agnostic neoplasms such as smooth muscle tumors, fibrous or myofibroblastic neoplasms, neurogenic tumors, vascular tumors, and a plethora of sarcomas. Select tumors show classic sites of origin within the prostate. While stromal tumors of uncertain malignant potential (STUMPs) commonly involve the peripheral zone at the prostate base, leiomyomas typically originate from the central prostate toward the apex. Some "prostatic" neoplasms such as gastrointestinal stromal tumors, solitary fibrous tumor (SFT), paragangliomas, and neurogenic tumors arise primarily from periprostatic soft tissues. Most mesenchymal tumors of the prostate and seminal vesicles manifest as large tumors that cause nonspecific symptoms; prostate-specific antigen level is not typically elevated. Diverse mesenchymal neoplasms demonstrate characteristic histopathologic and immunocytochemical features and variable cross-sectional imaging findings. While leiomyoma and SFT typically display low signal intensity on T2-weighted images, synovial sarcomas commonly show hemorrhage. Diagnosis is difficult because of the rarity and lack of awareness of the tumors and the significant overlap in histopathologic features. Select tumors show characteristic genetic abnormalities that allow the diagnosis to be established. For example, more than 90% of SFTs are characterized by a unique NAB2-STAT6 gene fusion, and more than 95% of synovial sarcomas are associated with a distinctive SYT-SSX chimeric transcript. Accurate diagnosis is imperative for optimal management owing to markedly different tumor biology as well as attendant therapeutic and prognostic implications. While STUMPs commonly recur, sarcomas typically charter an aggressive course with poor prognosis. Online supplemental material is available for this article. ^©RSNA, 2022.

Epithelioid angiomyolipoma: a pathological entity discovered in Verona with the endorsement of Doctor Rosai

In this manuscript, we summarize the main features of angiomyolipoma highlighting the recognition of epithelioid angiomyolipoma and the discovery of immunohistochemical expression of HMB45 in a group of tumors that now are referred to as as PEComas. In this scenario, Dr. Rosai believed in our intuition, demonstrating his intellectual honesty and motivated us with his experience (“when a tumor seems malignant it is malignant”) and enthusiasm for the new entities (“in Verona, you use HMB45 instead of H&E”). He really pushed the improvement of the knowledge in this field.

Cathepsin K: A Novel Diagnostic and Predictive Biomarker for Renal Tumors

Simple Summary

Our understanding of renal tumors has increased in the last years with the description of several novel entities. The expanding morphological spectrum complicates the pathologist’s diagnosis, often requiring immunohistochemical analysis. The role of cathepsin K immunoexpression is widened as a diagnostic tool in several renal tumors. This review describes the usefulness of cathepsin K in the differential diagnosis of renal neoplasms, highlighting the biological knowledge underpinning its expression. Moreover, cathepsin K seems to be a downstream marker of different genetic alterations, with a possible role as a predictive marker that may prospectively guide the development of therapeutic approaches as a molecular target.

Abstract

Cathepsin K is a papain-like cysteine protease with high matrix-degrading activity. Among several cathepsins, cathepsin K is the most potent mammalian collagenase, mainly expressed by osteoclasts. This review summarizes most of the recent findings of cathepsin K expression, highlighting its role in renal tumors for diagnostic purposes and as a potential molecular target. Indeed, cathepsin K is a recognized diagnostic tool for the identification of TFE3/TFEB-rearranged renal cell carcinoma, TFEB-amplified renal cell carcinoma, and pure epithelioid PEComa/epithelioid angiomyolipoma. More recently, its expression has been observed in a subgroup of eosinophilic renal neoplasms molecularly characterized by TSC/mTOR gene mutations. Interestingly, both TSC mutations or TFE3 rearrangement have been reported in pure epithelioid PEComa/epithelioid angiomyolipoma. Therefore, cathepsin K seems to be a downstream marker of TFE3/TFEB rearrangement, TFEB amplification, and mTOR pathway activation. Given the established role of mTOR inhibitors as a pharmacological option in renal cancers, cathepsin K could be of use as a predictive marker of therapy response and as a potential target. In the future, uropathologists may implement the use of cathepsin K to establish a diagnosis among renal tumors with clear cells, papillary architecture, and oncocytic features.

Perivascular epithelioid cell tumor (PEComa) of the kidney: an overview of its management and outcomes

Perivascular epithelioid cell tumor (PEComa) is a rare mesenchymal tumor with unique histological and immunohistochemical characteristics. Malignant renal cell carcinoma is even rarer and its biological behavior is still not clear. We report here a case of malignant PEComa in a male patient. The first symptom of the patient was intermittent hematuria. Ultrasound and computed tomography scan showed a solid mass in the left kidney. Fibrosarcoma was initially diagnosed after radical resection of the tumor. Six years later, the patient had a tumor recurrence and underwent a second operation, through which the diagnosis of renal malignant PEComa was made. Since then, the patient received chemotherapy, a third operation, and interventional treatment because of recurrence and metastasis of the tumor, which prolonged the life of the patient for another 6 years. Malignant PEComa involving the kidney is very rare; it seems to develop slowly but will recur and metastasize. At present, surgical resection remains the best treatment.

The Differential Diagnosis of Medullary-Based Renal Masses

CONTEXT.—

Renal malignancies can be divided into cortical- and medullary-based tumors, the latter of which classically infiltrate the renal parenchyma by extending between nonneoplastic structures. Although high-grade cortical tumors can rarely exhibit the same growth pattern, the infiltrative morphology should elicit a differential diagnosis to be considered in each case. However, these diagnoses can be challenging to distinguish, especially on small renal biopsy samples.

OBJECTIVE.—

To provide an overview of the clinical, gross, and microscopic findings; genetic and molecular alterations; and immunohistochemical evaluation of medullary-based renal tumors and other tumor types with overlapping morphologies and growth patterns.

DATA SOURCES.—

Literature review and personal observations were used to compile the information in this review.

CONCLUSIONS.—

Collecting duct carcinoma is a prototypical medullary-based tumor, and although diagnostic criteria exist, it remains a diagnosis of exclusion, especially with ancillary techniques aiding the recognition of established as well as more recently described neoplasms. Other medullary-based malignancies included in the differential diagnosis include renal medullary carcinoma/renal cell carcinoma unclassified with medullary phenotype, fumarate hydratase-deficient renal cell carcinoma, and upper tract urothelial carcinoma. Moreover, other rare entities should be excluded, including metastatic carcinoma, lymphoma, and melanoma. In addition to potential prognostic differences, accurate diagnoses can have important surgical and clinical management implications.

Characterization of Clinical Cases of Malignant PEComa via Comprehensive Genomic Profiling of DNA and RNA

PURPOSE

Perivascular epithelioid cell tumor (PEComa) is a rare mesenchymal soft tissue neoplasm often linked to mTOR pathway activation via TSC2 mutation. We analyzed a series of 31 consecutive metastatic PEComa (mPEComa) cases using a combined DNA/RNA hybrid capture-based comprehensive genomic profiling (CGP) assay to assess the genomic landscape of mPEComa.

PATIENTS AND METHODS

Formalin-fixed, paraffin-embedded (FFPE) blocks or slides were obtained from tumors from 31 unique patients with mPEC-oma. DNA and RNA were extracted and CGP was performed on 405 genes using a targeted next-generation sequencing (NGS) assay in a CLIA-certified lab.

RESULTS

All cases had locally advanced or metastatic disease, and 58% of patients were female with a median age of 50 years (range 8-76), and 17 and 14 specimens were from primary and metastatic sites, respectively. One hundred genomic alterations were identified in the cohort, with an average of 3.2 genomic alterations/case including alterations in TSC2 32.3% of cases (10), TSC1 9.6% (3), TFE3 16.1% (5, all fusions), and folliculin (FLCN) 6.4% (2), with all occurring in mutually exclusive fashion. Of TSC2 mutant cases, 70% had biallelic inactivation of this locus, as were 100% of TSC1 mutant cases. Two TSC1/2 wildtype cases harbored truncating mutations in FLCN, both of which were under LOH. Five TFE3 fusion cases were identified including the novel 5' fusion partner ZC3H4.

CONCLUSIONS

We describe for the first time mPEComa cases with FLCN mutations under LOH, further characterizing dysregulation of the mTOR pathway as a unifying theme in mPEC-oma. Cumulatively, we demonstrate the feasibility and potential utility of segregating mPEComa by TSC, TFE3, and FLCN status via CGP in clinical care.

Complexity of PEComas : Diagnostic approach, molecular background, clinical management

Perivascular epithelioid cell neoplasms (PEComas) are a family of mesenchymal neoplasms with features of both melanotic and smooth muscle differentiation. PEComa morphology is highly variable and encompasses epithelioid to spindle cells often with clear cytoplasm and prominent nucleoli. Molecularly, most PEComas are defined by a loss of function of the TSC1/TSC2 complex. Additionally, a distinct small subset of PEComas harboring rearrangements of the TFE3 (Xp11) gene locus has been identified. By presenting a series of three case reports with distinct features, we demonstrate diagnostic pitfalls as well as the importance of molecular work-up of PEComas because of important therapeutic consequences.

Epithelioid angiomyolipoma with tumor thrombus in IVC and right atrium

Epithelioid angiomyolipoma is an uncommon subtype of renal angiomyolipoma associated with potentially malignant behavior and is considered a distinct entity by the World Health Organization classification of renal tumors. We present a case of an epithelioid variant of angiomyolipoma with extension into the renal vein, inferior vena cava reaching up to the right atrium. Pre-operatively, a diagnosis of renal cell carcinoma was considered based on imaging findings. Intra-operatively due to extensive adhesions, surgical resection was not performed and only tissue sampling was performed for histopathology. Microscopic examination revealed short fascicles of spindle cells and perivascular epithelioid cells. A differential diagnosis of renal cell carcinoma with sarcomatoid differentiation was considered. The immunohistochemical profile showed tumor cells that express Melan-A and smooth muscle actin, while they were negative for pan-cytokeratin, PAX8, CK7, CD117 and CD34. Therefore a diagnosis of epithelioid angiomyolipoma was rendered. The presence of intravascular thrombi on radiological investigation and carcinoma-like growth pattern on light microscopy may compound an erroneous diagnosis of renal cell carcinoma. Hence, it is prudent for the urologist to consider differential diagnosis other than renal cell carcinoma when confronted with a renal neoplasm presenting with intravascular thrombi. In these cases, a core biopsy should be planned pre-operatively and diagnosis should be made with aid of appropriate immunohistochemical markers.

Parvalbumin immunohistochemical expression in the spectrum of perivascular epithelioid cell (PEC) lesions of the kidney

Parvalbumin is a cytosolic calcium-binding protein expressed in the distal convoluted tubule of the renal nephron. Among epithelial renal tumors, the reactivity for parvalbumin is observed in chromophobe renal cell carcinomas and frequently in oncocytomas. On the other hand, there are no data available on parvalbumin expression in the mesenchymal tumors of the kidney. Therefore, the purpose of this study was to evaluate the expression of parvalbumin in the spectrum of PEC (perivascular epithelioid cells) lesions of the kidney. Sixty-six PEC lesions (37 classic angiomyolipomas, 10 microscopic angiomyolipomas, 7 epithelioid angiomyolipomas/pure epithelioid PEComas, 5 leiomyoma-like angiomyolipomas, 3 lipoma-like angiomyolipomas, 2 intraglomerular lesions, 1 angiomyolipoma with epithelial cysts (AMLEC), and 1 sclerosing angiomyolipoma) were immunohistochemically stained with parvalbumin. Overall, parvalbumin immunostain was found in fifty-six PEC lesions (85%) and absent in the remaining ten cases (15%). Classic angiomyolipomas were positive in almost all cases (97%). Intraglomerular lesions and AMLEC showed parvalbumin immunolabeling as well. None of the 7 epithelioid angiomyolipomas/pure epithelioid PEComas or the only sclerosing angiomyolipoma expressed parvalbumin. In conclusion, we demonstrated the immunolabeling of parvalbumin in almost all PEC lesions of the kidney, but not in the epithelioid angiomyolipoma/pure epithelioid PEComa. This finding could shed light on some biological characteristics observed in the PEC lesions such as the plasticity of their cellular component. Moreover, parvalbumin may be another useful tool in the differential diagnosis among epithelioid angiomyolipoma/pure epithelioid PEComa with other renal eosinophilic tumors, such as oncocytoma and chromophobe renal cell carcinoma.

Primary Renal Mesenchymal Neoplasms in Nephrectomy Specimens: A 16-Year Survey of Primary and Incidental Cases From a Single Institution

Context. Primary renal mesenchymal neoplasms are rare but diverse. Several neoplasms of mesenchymal derivation can arise as a primary renal mass; however, incidental tumors are identified in nephrectomies performed for end-stage renal disease or other malignant epithelial renal neoplasms. In this article, we document their frequencies with demographic information in nephrectomy specimens. Design. We retrospectively searched our database for nephrectomy specimens from the year 2000 to 2016. Results. A total of 224 cases were identified with an incidence rate of 4.4% (224/5128). One hundred ninety (85%) neoplasms were benign, 27 (12%) were malignant, and 7 (3%) were of intermediate biologic behavior. The majority of cases occurred in adults (93%, 208/224), and 39% of cases represented an incidental finding. The most common neoplasms were angiomyolipoma (58%) and renomedullary interstitial cell tumor (17%). Malignant mesenchymal kidney tumors are rare (0.39% of nephrectomy specimens). The most common adults' malignant tumors in our survey were synovial sarcoma and Ewing's sarcoma. Conclusion. Primary renal mesenchymal tumors are rare and are mostly benign in nature with many incidentally identified lesions. They arise in different age groups with malignant lesions usually presenting at a younger mean age.

Perivascular Epithelioid Cell Tumor of the Urinary Bladder: A Systematic Review

Perivascular epithelioid cell tumor (PEComa) of the urinary bladder is a rare neoplasm showing distinct melanocytic and smooth muscle differentiation. We aimed to review the clinicopathologic features of bladder PEComa using all the available cases in the literature, along with 2 new cases from our database. The patients included 15 females and 15 males with a mean age of 39.2 ± 15.3 years. Painless hematuria was the most common clinical presentation. The tumors were usually well circumscribed with a mean tumor size of 4.4 ± 2.7 cm. Bladder PEComas demonstrated nests, trabeculae, or sheets of epithelioid cells with intermixed spindled cells and numerous thin-walled vessels. Immunohistochemical studies showed that the tumors were positive for HMB45 (27/27), cathepsin (4/4), SMA (20/22), and caldesmon (3/3) and were negative for pan cytokeratin (0/18) and EMA (0/4). Molecular studies revealed that PEComa was associated with the TFE3 (n = 3) and EWSR1 (n = 1) gene rearrangements. Treatment included partial cystectomy (n = 18), transurethral resection (n = 8), and radical cystectomy (n = 4). Twenty patients had no evidence of disease during a mean follow-up time of 19.4 ± 17.2 months. Two patients had recurrence, and 1 patient died of metastatic disease. In conclusion, bladder PEComas demonstrate distinct morphologic and immunohistochemical features. Although most tumors follow a benign course, a small subset may develop metastasis and cause death.

[Complexity of PEComas : Diagnostic approach, molecular background, clinical management (German version)]

Perivascular epithelioid cell neoplasms (PEComas) are a family of mesenchymal neoplasms with features of both melanotic and smooth muscle differentiation. PEComa morphology is highly variable and encompasses epithelioid to spindle cells often with clear cytoplasm and prominent nucleoli. Molecularly, most PEComas are defined by a loss of function of the TSC1/TSC2 complex. Additionally, a distinct small subset of PEComas harboring rearrangements of the TFE3 (Xp11) gene locus has been identified. By presenting a series of three case reports with distinct features, we demonstrate diagnostic pitfalls as well as the importance of molecular work-up of PEComas because of important therapeutic consequences.

Patterns of LC3A Autophagy Protein Expression in Keratoacanthomas

To investigate the expression patterns of autophagy marker light chain protein 3 (LC3A) in keratoacanthoma (KA). KAs are generally regarded as benign but malignant behavior, including rare metastases, may occur. 85 KAs were assessed for the LC3A autophagic protein by immunohistochemistry. Diffuse cytoplasmic staining and a "stone-like structure" (SLS) characterized positive expression. Thirty-four out of 85 KAs (40%) had diffuse cytoplasmic LC3A immunostaining (percentage of positive cells ranging from 5 to 60%). In contrast, only 4 of the 85 KAs (4.7%) expressed SLSs. Only one SLS was detected per histologic section of each tumor. The p53 oncoprotein was encountered in all cases with expression ranging from 1 to 90% of cells (median 30%). The Ki-67 index was expressed in 63 cases (74% of cases; range 1-50% of cells; median value 5%). Neither of these two parameters nor diffuse cytoplasmic LC3A staining was significantly correlated with SLS expression or lack thereof. Expression of SLSs, a hallmark of malignancy, was found in 4.7% of KAs. Further study is necessary to determine whether this fraction represents the exceptional cases that harbor latent malignant potential.

Fatty masses of the abdomen and pelvis and their complications

There are numerous common and rare macroscopic fat-containing masses found in the abdomen and pelvis. These include benign masses, such as lipoleiomyoma, ovarian teratoma, mesenteric teratoma, and lipoma, as well as malignant masses, including liposarcoma and malignant transformation of benign entities. Any mass may become symptomatic due to the development of a complication which may range from ovarian torsion to intussusception to hemorrhage. Imaging plays a vital role in diagnosis and treatment planning when confronted with a symptomatic fat-containing mass.

Mesenchymal Neoplasms of the Genitourinary System: A Selected Review with Recent Advances in Clinical, Diagnostic, and Molecular Findings

Mesenchymal neoplasms of the genitourinary (GU) tract often pose considerable diagnostic challenges due to their wide morphologic spectrum, relative rarity, and unexpected incidence at GU sites. Soft tissue tumors arise throughout the GU tract, whether from adventitia surrounding or connective tissues within the kidneys, urinary bladder, and male and female genital organs. This selected article focuses on a subset of these lesions, ranging from benign to malignant and encompassing a range of patterns of mesenchymal differentiation, where recent scholarship has lent greater insight into their clinical, molecular, or diagnostic features.

Renal manifestation of tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is a tumor predisposition syndrome with significant renal cystic and solid tumor disease. It commonly causes several types of cystic disease and benign tumors (angiomyolipomata) in the kidneys that can both lead to significant premature loss of glomerular filtration rate. The main risks of angiomyolipomata, severe bleeding, loss of renal function, and pulmonary lymphangioleiomyomatosis, can be ameliorated by active surveillance and preemptive therapy with mTOR inhibitors. The cystogenic mechanism may involve primary cilia, but also appears to also involve a majority of normal tubular cells and may be driven by a minority of cells with mutations inactivating both their TSC1 or TSC2 genes. Malignant tumors are rare.

t(6;11) renal cell carcinoma: a study of seven cases including two with aggressive behavior, and utility of CD68 (PG-M1) in the differential diagnosis with pure epithelioid PEComa/epithelioid angiomyolipoma

Renal cell carcinomas with t(6;11) chromosome translocation involving the TFEB gene are indolent neoplasms which often occur in young patients. In this study, we report seven cases of renal cell carcinoma with TFEB rearrangement, two of whom had histologically proven metastasis. Patients (4F, 3M) ranged in age from 19 to 55 years (mean 37). One patient developed paratracheal and pleural metastases 24 months after surgery and died of disease after 46 months; another one recurred with neoplastic nodules in the perinephric fat and pelvic soft tissue. Histologically, either cytological or architectural appearance was peculiar in each case whereas one tumor displayed the typical biphasic morphology. By immunohistochemistry, all tumors labelled for cathepsin K, Melan-A and CD68 (KP1 clone). HMB45 and PAX8 staining were detected in six of seven tumors. All tumors were negative for CD68 (PG-M1 clone), CKAE1-AE3, CK7, CAIX, and AMACR. Seven pure epithelioid PEComa/epithelioid angiomyolipomas, used as control, were positive for cathepsin K, melanocytic markers, and CD68 (PG-M1 and KP1) and negative for PAX8. Fluorescence in situ hybridization results showed the presence of TFEB gene translocation in all t(6;11) renal cell carcinomas with a high frequency of split TFEB fluorescent signals (mean 74%). In the primary and metastatic samples of the two aggressive tumors, increased gene copy number was observed (3-5 fluorescent signals per neoplastic nuclei) with a concomitant increased number of CEP6. Review of the literature revealed older age and larger tumor size as correlating with aggressive behavior in these neoplasms. In conclusion, we present the clinical, morphological and molecular features of seven t(6;11) renal cell carcinomas, two with histologically demonstrated metastasis. We report the high frequency of split signals by FISH in tumors with t(6;11) chromosomal rearrangement and the occurrence of TFEB gene copy number gains in the aggressive cases, analyzing either the primary or metastatic tumor. Finally, we demonstrate the usefulness of CD68 (PG-M1) immunohistochemical staining in distinguishing t(6;11) renal cell carcinoma from pure epithelioid PEComa/epithelioid angiomyolipoma.

Renal Tumors of Childhood: Radiologic-Pathologic Correlation Part 2. The 2nd Decade: From the Radiologic Pathology Archives

Malignant renal tumors account for 7% of childhood cancers, and Wilms tumors are by far the most common-but not in older children and adolescents. Among individuals in the latter half of their 2nd decade of life, renal cell carcinoma (RCC) is more common than Wilms tumor. The histopathologic spectrum of RCCs in children differs from that in adults. The most common subtype of RCC in children and adolescents is Xp11.2 translocation RCC, which is distinguished by hyperattenuation at nonenhanced computed tomography, a defined capsule, and associated retroperitoneal lymphadenopathy. Papillary RCC is the second most common histologic subtype. It enhances less intensely compared with the adjacent renal parenchyma and has a propensity for calcification. Clear cell RCC is seen in patients with von Hippel-Lindau disease and is distinguished by its relatively hypervascular nature. Medullary carcinoma affects adolescents with the sickle cell trait and is characterized by an infiltrative growth pattern and extensive metastasis at presentation. Angiomyolipoma is seen in children with tuberous sclerosis complex and is often multifocal and hypervascular, with macroscopic fat. Metanephric tumors are central, circumscribed, and typically calcified. Lymphoma usually manifests as multifocal masses, but it may involve a solitary mass or infiltrative pattern. Extensive adenopathy and involvement of the gastrointestinal tract or other organs also may be seen. Primitive neuroectodermal tumor is an aggressive neoplasm that is typically quite large at diagnosis. Knowledge of the clinical, biologic, and histopathologic features of renal tumors in older children and adolescents and their effects on the imaging appearance can help the radiologist offer a useful preoperative differential diagnosis.

Evidence of renal angiomyolipoma neoplastic stem cells arising from renal epithelial cells

Renal angiomyolipomas (AML) contain an admixture of clonal tumour cells with features of several different mesenchymal lineages, implying the existence of an unidentified AML neoplastic stem cell. Biallelic inactivation of TSC2 or TSC1 is believed to represent the driving event in these tumours. Here we show that TSC2 knockdown transforms senescence-resistant cultured mouse and human renal epithelial cells into neoplastic stem cells that serially propagate renal AML-like tumours in mice. mTOR inhibitory therapy of mouse AML allografts mimics the clinical responses of human renal AMLs. Deletion of Tsc1 in mouse renal epithelia causes differentiation in vivo into cells expressing characteristic AML markers. Human renal AML and a renal AML cell line express proximal tubule markers. We describe the first mouse models of renal AML and provide evidence that these mesenchymal tumours originate from renal proximal tubule epithelial cells, uncovering an unexpected pathological differentiation plasticity of the proximal tubule.

Renal angiomyolipomas (AML) contain a mix of clonal tumour cells. Here, through reverse tumour engineering experiments, mouse genetics and analyses of human AML tumours, the authors provide evidence that these mesenchymal tumours originate from renal proximal tubule epithelial cells.

Challenge of FNA diagnosis of angiomyolipoma: A study of 33 cases

BACKGROUND

Angiomyolipoma (AML), typically composed of smooth muscle, vessels, and fat, is generally a benign tumor in the kidneys. However, it occasionally occurs in extrarenal sites and behaves like a malignant tumor. AML is uncommonly encountered in fine-needle aspiration (FNA) samples and can cause diagnostic difficulty.

METHODS

We searched our pathology database for FNA cases diagnosed between 2003 and 2015 that were subsequently confirmed to be AML in the same lesion by surgical pathologic evaluation. The diagnostic performance, challenges, and cytologic features were retrospectively reviewed.

RESULTS

In total, 33 FNA cases from 31 patients were identified. The final surgical pathologic diagnoses included 30 primary AMLs (28 in kidneys and 2 in liver) and 3 were metastases (in liver, lung, and abdominal wall, respectively). Aspiration sites included kidney/retroperitoneum (n = 28), abdominal wall (n = 1), lung (n = 1), and liver (n = 3). The FNA diagnoses were consistent with/favor AML (n = 16), descriptive (n = 12), nondiagnostic (n = 2), and erroneous (n = 3). Of the 3 erroneous cases, 2 were diagnosed as renal cell carcinoma, and 1 was diagnosed as a pleomorphic malignant neoplasm. Cytologically, cases with predominantly spindle cells were the most commonly encountered (n = 19). Cases with predominantly epithelioid cells (n = 6) can pose a diagnostic difficulty and were observed in all 3 metastatic AMLs and in 2 of the 3 erroneous cases. Immunostains were performed on 11 FNAs and helped the diagnosis in 9 cases.

CONCLUSIONS

FNA diagnosis of AML may be challenging, especially in cases with a predominantly epithelioid component and/or an extrarenal location. Immunostaining is important to improve diagnostic accuracy of this rare entity. Cancer Cytopathol 2017;125:257-266. © 2016 American Cancer Society.

Pigmented perivascular epithelioid cell tumor (PEComa) arising from kidney: A case report

INTRODUCTION

Perivascular epithelioid cell tumor (PEComa) is a mesenchymal neoplasm composed of perivascular epithelioid cells with clear to eosinophilic cytoplasm. Pigmented PEComa arising from kidney is extraordinarily rare and sometimes can exhibit aggressive biological behavior.

CASE REPORT

We present here a rare case of pigmented renal PEComa in a 46-year-old female. The patient had complained of lumbago complicated with nausea and vomiting for 2 weeks and therefore was referred to our department. An enhanced computed scan revealed a 4 × 3 × 3 cm round-like mass in the lower pole of right kidney with inhomogeneous enhancement. The tumor cells immunestained was positive for HMB-45, focally positive for c-Kit (CD117), and negative for vimentin, S-100, AE1/AE3, CK-7, CK-18, CD-10, RCC antigen, CgA, DOG-1, EMA, smooth muscle actin, and synaptophysin. We successfully performed 3-dimensional laparoscopic resection of the neoplasm, which was then diagnosed as pigmented PEComa by postoperative pathology. No further growing lesion or metastasis was observed during a 1-year follow-up.

CONCLUSION

This case report shows that pigmented renal PEComa is often presented as a renal mass with nonspecific symptoms and imaging features. The gold diagnosis of renal pigmented PEComa is mainly based on the combination of histopathology and immunohistochemistry. Complete resection by 3-dimensional laparoscopic nephron-sparing surgery can be an effective therapeutic management.

Xp11 neoplasm with melanocytic differentiation of the prostate harbouring the novel NONO-TFE3 gene fusion: report of a unique case expanding the gene fusion spectrum

Recently, an increasing number of TFE3 rearrangement-associated tumours have been reported, such as TFE3 rearrangement-associated perivascular epithelioid cell tumours (PEComas), melanotic Xp11 translocation renal cancers and melanotic Xp11 neoplasms. We have suggested that these tumours belong to a single clinicopathological spectrum. 'Xp11 neoplasm with melanocytic differentiation' or 'melanotic Xp11 neoplasm' have been proposed to designate this unique neoplasm. Herein, we describe the first case of an Xp11 neoplasm with melanocytic differentiation to be described in the prostate, bearing the novel NONO-TFE3 gene fusion. This study both adds to the spectrum regarding melanotic Xp11 neoplasms and expands its gene fusion spectrum. Moreover, we discuss the relationship of these rare tumours to neoplasms such as conventional PEComas, alveolar soft part sarcomas, malignant melanomas, clear cell sarcomas and Xp11 translocation renal cancers.

[Mesenchymal tumors of the urinary bladder]

Mesenchymal tumors and tumor-like lesions of the urinary bladder are rare. They encompass a heterogeneous group of reactive pseudosarcomatous tumor-like changes and benign neoplastic lesions as well as malignant neoplasms (sarcomas) with variable biological behavior. The well-known differential diagnostic difficulties related to these conditions are mainly due to their rarity and thus limited experience and familiarity with their histological features and due to the significant morphological overlap between fully benign reactive conditions and aggressive malignant neoplasms. The distinction between them may on occasion represent a real challenge and is associated with several pitfalls. This overview summarizes the clinicopathological and differential diagnostic aspects of the most important lesions and discuss their differential diagnosis in the light of current knowledge.

PSF/SFPQ is a very common gene fusion partner in TFE3 rearrangement-associated perivascular epithelioid cell tumors (PEComas) and melanotic Xp11 translocation renal cancers: clinicopathologic, immunohistochemical, and molecular characteristics suggesting classification as a distinct entity

An increasing number of TFE3 rearrangement-associated tumors, such as TFE3 rearrangement-associated perivascular epithelioid cell tumors (PEComas), melanotic Xp11 translocation renal cancers, and melanotic Xp11 neoplasms, have recently been reported. We examined 12 such cases, including 5 TFE3 rearrangement-associated PEComas located in the pancreas, cervix, or pelvis and 7 melanotic Xp11 translocation renal cancers, using clinicopathologic, immunohistochemical, and molecular analyses. All the tumors shared a similar morphology, including a purely nested or sheet-like architecture separated by a delicate vascular network, purely epithelioid cells displaying a clear or granular eosinophilic cytoplasm, a lack of papillary structures and spindle cell or fat components, uniform round or oval nuclei containing small visible nucleoli, and, in most cases (11/12), melanin pigmentation. The levels of mitotic activity and necrosis varied. All 12 cases displayed moderately (2+) or strongly (3+) positive immunoreactivity for TFE3 and cathepsin K. One case labeled focally for HMB45 and Melan-A, whereas the others typically labeled moderately (2+) or strongly (3+) for 1 of these markers. None of the cases were immunoreactive for smooth muscle actin, desmin, CKpan, S100, or PAX8. PSF-TFE3 fusion genes were confirmed by reverse transcription polymerase chain reaction in cases (7/7) in which a novel PSF-TFE3 fusion point was identified. All of the cases displayed TFE3 rearrangement associated with Xp11 translocation. Furthermore, we developed a PSF-TFE3 fusion fluorescence in situ hybridization assay for the detection of the PSF-TFE3 fusion gene and detected it in all 12 cases. Clinical follow-up data were available for 7 patients. Three patients died, and 2 patients (cases 1 and 3) remained alive with no evidence of disease after initial resection. Case 2 experienced recurrence and remained alive with disease. Case 5, a recent case, remained alive with extensive abdominal cavity metastases. Our data suggest that these tumors belong to a single clinicopathologic spectrum and expand the known characteristics of TFE3 rearrangement-associated tumors.