Perivascular epithelioid cell neoplasms (PEComas): four malignant cases expanding the histopathological spectrum and a description of a unique finding

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.

Laparoscopic radical nephroureterectomy in the oblique supine lithotomy integrative position for rare renal malignant perivascular epithelioid cell tumor with renal vein cancerous thrombosis: A case report and literature review

RATIONALE

Perivascular epithelioid cell tumor (PEComa) is a mesenchymal tumor that arises from perivascular epithelioid cells and can differentiate into melanocytes and smooth muscle cells. Malignant renal perivascular epithelioid cell tumor is extremely rare. Due to the lack of specific clinical manifestations and imaging features, diagnosing PEComa depends on postoperative pathology and immunohistochemistry. Surgery is the primary treatment for malignant PEComa because the efficacy of radiotherapy and chemotherapy is uncertain. There is still a lack of unified diagnostic criteria and treatment guidelines for renal malignant PEComa, especially with vascular invasion. Hence, the treatment experience depends on a small number of cases reported worldwide.

PATIENT CONCERNS

A 68-year-old woman was admitted to our hospital due to intermittent hematuria for over 8 months. The color Doppler ultrasound and computed tomography scan revealed a mass in the lower middle part of the left kidney.

DIAGNOSIS

Rare renal malignant perivascular epithelioid cell tumor with renal vein cancerous thrombosis.

INTERVENTIONS

A laparoscopic radical left nephroureterectomy in the oblique supine lithotomy position was performed.

OUTCOMES

The operation process went smoothly, and no pulmonary embolism occurred after the operation. The final pathological diagnosis was a renal malignant perivascular epithelioid cell tumor. After a 12-month follow-up, no recurrence or metastasis was found.

LESSONS

Renal malignant PEComa is an extremely rare mesenchymal tumor diagnosed mainly based on pathology. Surgery is currently the effective treatment for malignant PEComa. For the surgical treatment of malignant renal PEComa with vascular invasion, laparoscopic radical nephroureterectomy in the oblique supine lithotomy integrative position has many benefits, as exemplified by our current case.

Perivascular Epithelioid Cell Tumor of Urinary Bladder

OBJECTIVES

To review the clinicopathologic features of perivascular epithelioid cell tumor (PEComa) of the urinary bladder.

METHODS

Seven cases of bladder PEComa were studied by light microscopy, immunohistochemistry, and fluorescence in situ hybridization (FISH).

RESULTS

In our 7 cases, 5 patients were female and 2 were male, with ages between 26 and 78 years. Patients presented with hematuria and recurrent abdominal discomfort as the main clinical symptoms. Microscopically, the epithelioid and spindle-shaped tumor cells with clear to granular eosinophilic cytoplasm were arranged in fascicular, acinar, or nested patterns. The tumor cells were positive for HMB45, melan-A, and SMA, but no TFE3 gene rearrangement was detected in any of the 7 samples by FISH. The analysis of all 35 cases from the literature and ours showed a patient age range from 16 to 78 years (mean age, 39 years), a male-to-female ratio of 1:1.3, maximal tumor diameters from 0.6 to 18.8 cm (mean, 4.5 cm). With a mean follow-up of 27 months, the recurrence, metastasis, and mortality rates were 10.7%, 10.7%, and 7.1%, respectively.

CONCLUSIONS

Bladder PEComa is extremely rare, remains a diagnostic challenge, and needs more attention. Strengthening the understanding of this tumor will improve diagnostic accuracy.

Retroperitoneal Sclerosing Angiomyolipoma with Long-Term Follow up: A Case Report with Unique Clinicopathologic and Genomic Profile

Sclerosing angiomyolipoma (sAML) is a rare variant of the perivascular epithelioid tumors exhibiting distinct morphology with extensive stromal hyalinization, which makes it challenging to recognize. It often lacks an adipose tissue component and melanocytic markers may be expressed only focally, further posing a diagnostic challenge. Here, we report a case of sAML of the left pararenal retroperitoneum in a 52-year-old woman with 92 months of clinical follow up and discuss the histologic features, immunoprofile, molecular alterations, and differential diagnoses that can aid in the diagnosis of this unique and rare entity.

PNL2: A Useful Adjunct Biomarker to HMB45 in the Diagnosis of Uterine Perivascular Epithelioid Cell Tumor (PEComa)

Perivascular epithelioid cell tumors (PEComa) are rare neoplasms characterized by co-expression of melanocytic and muscle markers. HMB45 and Melan-A are used to confirm a PEComa diagnosis; however, both are often focally expressed and sensitivity for Melan-A is low. PNL2 is a reliable biomarker for epithelioid melanoma and renal angiomyolipoma/PEComa. The objective of this study was to determine PNL2 utility in diagnosing uterine PEComas as well as distinguishing PEComas from uterine smooth muscle tumors (SMTs). Twenty-one uterine PEComas and 45 SMTs were analyzed for PNL2; a subset was also stained for HMB45, Melan-A, Cathepsin-K, Desmin, and h-Caldesmon. Cases were scored as negative (0), focal (<10% of tumor cells), or patchy to diffusely positive (>10% of tumor cells). PEComas were positive for PNL2, HMB45, and Melan-A in 86%, 100%, and 57% of cases, respectively. In PEComas, PNL2 was patchy to diffusely positive more frequently (10/18, 56%) than Melan-A (4/12, 33%). In contrast, 2 of 45 (4%) SMTs were focally PNL2 positive; HMB45 was focally positive in 4 SMTs (11%) and all were negative for Melan-A. Desmin and h-Caldesmon were positive in 90% and 57% of PEComas, and 91% and 82% of SMTs. Cathepsin-K was positive in 100% of PEComas and 93% of SMTs. PNL2 is a useful biomarker for the diagnosis of uterine PEComa, with comparable sensitivity and specificity to HMB45. In contrast, PNL2 stains more PEComas when compared with Melan-A. Cathepsin-K, Desmin, and h-Caldesmon are of little utility for distinguishing PEComas and SMTs; however, lack of Cathepsin-K argues against PEComa. These results suggest that PNL2 should be used in conjunction with HMB45 in the diagnosis of PEComa of the uterine corpus.

Bladder perivascular epithelioid cell neoplasm: The importance of immunohistochemistry in the diagnosis of an unusual neoplasm

Perivascular epithelioid cell neoplasms represent a group of uncommon mesenchymal tumours with as yet undiscovered benign counterpart. Although perivascular epithelioid cell neoplasms have been described arising in most organ systems as well as in soft tissue and bone, only a small number of perivascular epithelioid cell neoplasms have been reported in the bladder. To date, there is no agreed system for predicting the behaviour of these tumours. We describe a case of a perivascular epithelioid cell neoplasm of the bladder arising in a 57-year-old male and initially diagnosed on biopsy and present a review of the literature focussing on the pathological differential diagnosis and the importance of key histological features in conjunction with a broad immunohistochemical panel. This case report highlights the key features of bladder perivascular epithelioid cell neoplasms that distinguishes these rare neoplasms from other bladder lesions.

Histopathologic Characterization of Bladder Perivascular Epithelioid Cell Neoplasms (PEComa): A Series of 11 Cases With a Subset Having TFE3 Rearrangements

Perivascular epithelioid cell neoplasms (PEComas) of the bladder are extremely rare, with ~30 case reports. A subset of PEComas contain TFE3 gene rearrangement, however, the distinct histomorphologic features of these translocation tumors has not been fully explored in bladder PEComas. In our series, 11 cases of bladder PEComas were collected, including 1 internal and 10 consults, with 1 case previously reported. There was a female predominance (9 female, 2 male) with a mean age of 44.2 years (24 to 61 y). In only 1 of the 10 consult cases was PEComa considered in the differential diagnosis. In 10 of 11 cases, prominent epithelioid features were noted, with the final case having focal epithelioid morphology. Mitotic rate was increased in 2 of 11 cases, and 2 of 11 cases had cytological atypia. Two cases were malignant, with invasion into perivesicle tissue in 1 case, and metastases to lungs and brain followed by death in the other case. Immunohistochemically, there was strong, and diffuse staining for cathepsin K in 10/11 cases with the 1 negative case restained on a previously stained slide. HMB-45 was diffusely positive in 8/11 cases, while melan-A was present in only 1/10 cases. Muscle markers were variably expressed with positivity for both smooth muscle actin in 6/10 cases and desmin in 3/10 cases. Keratin AE1/3 was uniformly negative (0/11). In 5/8 cases where TFE3 was rearranged by fluorescence in situ hybridization, the morphology had a predominantly epithelioid, nested architecture. Overall, bladder PEComas are particularly difficult to diagnose given their rarity, are predominantly epithelioid and do not always express melanocytic markers. Diagnosis in the bladder requires a combination of morphologic characterization, exclusion of other diagnostic possibilities, positive Cathepsin K staining, variable melanocytic marker expression, with some cases showing a TFE3 gene rearrangement.

Malignant Epithelioid Neoplasm of the Brain

Malignant epithelioid tumors have been described in various organ systems, but are rarely seen in the brain. They are aggressive tumors and have high mortality. In certain cases, the immunohistochemistry (IHC) findings may not be sufficient to clarify the diagnosis. In these cases, next-generation genetic sequencing may play a role in clarifying the diagnosis. In addition to lab testing, a thorough history and physical exam are necessary to rule out other sources of the tumor such as melanoma. Patients presenting with neurological symptoms are cared for by a wide variety of physicians, hence it is important to raise awareness of rare tumors in order to provide timely and appropriate management and referral for these patients. We present the case of a middle-aged woman who was diagnosed with a ‘malignant epithelioid neoplasm’ of the brain, a rare variety of tumors. We also give the clinical course of this illness.

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.

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.

Rheb/mTOR/p70s6k Cascade and TFE3 Expression in Conventional and Sclerosing PEComas of the Urinary Tract

Perivascular epithelioid cell tumors (PEComas) are rarely found in the urinary tract. The clinicopathologic characteristics of 10 cases, retrospectively collected from 5 medical institutions in 3 different European countries, are presented in this study. Male/female ratio was 3:7 and the average age at diagnosis was 62.7 years. Nine cases were sporadic and 1 showed germline mutation of the TSC2 gene. Eight cases were located in the kidney, 1 in the left adrenal and 1 in the right ureter. All of the patients were alive and free of disease at the time of last contact (mean follow-up, 14.1 mo). Four cases displayed a conventional morphology and 6 showed a prominent sclerotic stroma. By immunohistochemistry, melanocytic markers were consistently expressed, especially HMB-45 (10 cases), MiTF (9 cases), and Melan-A (6 cases). Desmin was expressed in 6 cases; 2 cases were positive for CD117; a single case showed TFE3 expression. pMAPK, mTOR, and pAKT demonstrated variable immunostaining with focal positivity in 7, 4, and 2 cases, respectively. Cytokeratins were repeatedly negative in all cases. PEComas in the urinary tract, especially in the renal region, may show a relatively high frequency of the sclerosing histologic subtype. Knowledge of the distinct histology and immunohistochemical profile is vital to correctly diagnose this rare entity.

Malignant PEComa With Metastatic Disease at Diagnosis and Resistance to Several Chemotherapy Regimens and Targeted Therapy (m-TOR Inhibitor)

Perivascular epithelioid cell tumors (PEComas) are infrequent neoplasms with peculiar myomelanocytic differentiation. The aggressive abdominopelvic variant is rare, with only a small number of published cases. We present an additional case of this unusual variant, which showed an aggressive histologic and clinical behavior with multiple liver metastases and resistance to several therapies. We also discuss the histological and immunohistochemical profiles as well as the differential diagnosis.

PEComa: morphology and genetics of a complex tumor family

Perivascular epithelioid cell tumors, or PEComas, are mesenchymal neoplasms composed of histologically and immunohistochemically distinctive epithelioid or spindle cells, which are immunoreactive for both smooth muscle and melanocytic markers. The cells in PEComas are typically arranged around blood vessels and appear to form the vessel wall, often infiltrating the smooth muscle of small- to medium-sized vessels. Periluminal cells are usually epithelioid and the more peripheral cells are spindle shaped. The cells have small, round to oval nuclei, sometimes with focal nuclear atypia, and clear to eosinophilic cytoplasm, and no counterpart normal cell has been identified. The PEComa "family" now includes angiomyolipoma, pulmonary clear cell "sugar" tumor and lymphangioleiomyomatosis, primary extrapulmonary sugar tumor, clear cell myomelanocytic tumor of the falciform ligament/ligamentum teres, abdominopelvic sarcoma of perivascular epithelioid cells, and other tumors with similar features at various sites that are simply termed PEComa. Some PEComas occur in patients with tuberous sclerosis complex and share the genetic abnormalities. There is a behavioral spectrum from benign to frankly malignant, and histologic criteria have been proposed for assessing malignant potential. The differential diagnosis can include carcinomas, smooth muscle tumors, other clear cell neoplasms, and adipocytic tumors. PEComas constitute a genetically diverse group that includes neoplasms harboring TFE3 gene rearrangements and those with TSC2 mutations, indicating alternative tumorigenic pathways. Recent advances in therapy of malignant PEComas relate to increased knowledge of specific genetic changes and their effects on metabolic pathways that are susceptible to specific interventions. We review PEComas, emphasizing the diagnostic spectrum and recent immunohistochemical and genetic findings.

Malignant Perivascular Epithelioid Cell Tumor (PEComa) of the Adrenal Gland: Report of a Rare Case Posing Diagnostic Challenge with the Role of Immunohistochemistry in the Diagnosis

Histological diagnosis of adrenal tumors is often challenging as diverse groups of tumors, both primaries and metastatic, may be seen in the adrenal gland with overlapping morphological features. Immunohistochemistry (IHC) plays the most important role in their diagnosis. Perivascular epithelioid cell tumor (PEComa), a rarely reported tumor in the adrenal gland, shares many features with another rare tumor sarcomatoid adrenocortical carcinoma (ACC). Extensive immunohistochemical study is required to distinguish this tumor from adrenocortical carcinoma and from other morphologically similar tumors. The unique combination of immunoreactivity for melanocytic markers, such as HMB-45 and Melan A, and myogenic markers, such as smooth muscle actin, is the hallmark of PEComas biological behavior, and prognosis of malignant PEComas is yet to be fully understood. Few cases of malignant PEComa have been reported in the adrenal gland. We report a case of malignant PEComa of the adrenal gland posing diagnostic challenge and compare its morphological and immunohistochemical features with those of sarcomatoid ACC.

Perivascular epithelioid cell tumor of gastrointestinal tract: case report and review of the literature

Perivascular epithelioid cell tumors of gastrointestinal tract (GI PEComas) are exceedingly rare, with only a limited number of published reports worldwide. Given the scarcity of GI PEComas and their relatively short follow-up periods, our current knowledge of their biologic behavior, molecular genetic alterations, diagnostic criteria, and prognostic factors continues to be very limited.We present 2 cases of GI PEComas, one of which showed an aggressive histologic behavior that underwent multiple combined chemotherapies. We also review the available English-language medical literature on GI PEComas-not otherwise specified (PEComas-NOS) and discuss their clinicopathological and molecular genetic features.Pathologic analyses including histomorphologic, immunohistochemical, and ultrastructural studies were performed to evaluate the clinicopathological features of GI PEComas, their diagnosis, and differential diagnosis. Immunohistochemistry, semiquantitative reverse transcriptase polymerase chain reaction, and DNA sequencing assays were carried out to detect the potential molecular genetic alterations in our cases. Microscopically, the tumors showed distinctive histologic features of PEComas-NOS, including fascicular or nested architecture, epithelioid or spindled cell type, and clear to eosinophilic cytoplasm. The tumor cells were immunohistochemically positive for melanocytic markers. Molecular pathological assays confirmed a PSF-TFE3 gene fusion in one of our cases. Furthermore, in this case microphthalmia-associated transcription factor and its downstream genes were found to exhibit elevated transcript levels.Knowledge about the molecular genetic alterations in GI PEComas is still limited and warrants further study.

Primary cutaneous perivascular epithelioid cell tumor: a clinicopathological and molecular reappraisal

BACKGROUND

Perivascular epithelioid cell tumor (PEComa) is a rare neoplasm of uncertain histogenesis with a mixed myomelanocytic immunophenotype, rarely arising in the skin (primary cutaneous PEComa [pcPEComa]).

OBJECTIVE

We analyzed the clinicopathological features of 8 pcPEComas, assayed for DNA copy number changes and for initiating mutations common in melanocytic neoplasms.

METHODS

pcPEComas were evaluated using immunohistochemistry, comparative genomic hybridization, and DNA sequencing.

RESULTS

pcPEComas were erythematous nodules, mostly in the lower extremities of women (5/8), composed of large pale-staining epithelioid cells. The patient's age range was 26 to 67 (mean 46) years. The percentages of tumors staining positively were as follows: micro-ophthalmia-associated transcription factor, NKI/C3, bcl-1, E-cadherin, and cathepsin K (100%); HMB-45, 4E-binding protein 1, and CD68 (88%); smooth muscle actin and muscle-specific actin (40%); S100 (38%); calponin (20%); desmin (13%); and melan-A, SOX10, and keratin (0%). No chromosomal copy number changes or initiating mutations were identified.

LIMITATIONS

Small sample size is a limitation.

CONCLUSIONS

pcPEComas have a different molecular signature than extracutaneous tumors and are unrelated to tuberous sclerosis. However, the common expression of 4E-binding protein 1 points to a role of the mTOR pathway in their pathogenesis. Because pcPEComas are diagnostically challenging, we propose that micro-ophthalmia-associated transcription factor, NKIC3, smooth muscle actin, desmin, bcl-1, cathepsin K, and 4E-binding protein 1 can be used when evaluating a possible pcPEComa.

Perivascular epithelioid cell tumour of the bladder

A 39-year-old woman presented with a long history of pelvic pain and urinary urgency. Prior workup by her primary care doctor had been negative. The patient's gynaecologist ultimately referred her to a urologist following an ultrasound that revealed a possible bladder mass. MRI of the abdomen and pelvis demonstrated a 4 cm soft tissue lesion arising from the bladder. Cystoscopy showed an atypical mass on the anterior bladder wall, and pathological examination of the TURBT (transurethral resection of the bladder tumour) specimen revealed a perivascular epithelioid cell tumour (PEComa) with involvement of the detrusor muscle. The patient underwent a robotically assisted laparoscopic partial cystectomy. Final pathology confirmed a PEComa with negative margins. The patient had an uncomplicated postoperative course and is doing well following surgery. A surveillance cystoscopy at 6 months showed no evidence of recurrence. This case underscores the variability of clinical presentation of PEComas while proposing an appropriate method of surgical management.

Malignant mesenteric perivascular epithelioid cell neoplasm presenting as an intra-abdominal fistula in a 49-year-old female

Perivascular epithelioid cell tumors are rare mesenchymal tumors arising from histologically and immunohistochemically distinctive perivascular epithelioid cells that express both myogenic and melanocytic markers. These tumors are known to arise from different organs in the body and usually have an unpredictable clinical course. We report a case of a 49-year-old female who presented with diffuse abdominal pain, fever, chills, and nonbilious vomiting for a day. Work-up revealed a mesenteric mass measuring 13.5 × 7.7 × 9.5 cm, arising in the mesentery of the hepatic flexure, with adjacent gas suggestive of fistularization into the right colon. An exploratory laparotomy with resection of the mesenteric mass was performed, and the initial histopathology results were compatible with either an adenocarcinoma or a sarcoma; however, because of poor differentiation it was difficult to make a definitive diagnosis. However, final histopathology results revealed a malignant perivascular epithelioid cell tumor (with reservation that a S100 negative metastatic melanoma must be excluded clinically). Following surgery the patient was started on everolimus, an m-TOR inhibitor, and has shown good response to this medication.

Pararenal sclerosing PEComa

Small renal or pararenal masses and retroperitoneum lesions are extremely difficult to diagnose. Imaging technology is a precious diagnostic tool; however, it places physicians in a difficult position since many lesions are not precisely diagnosed. Clinical and radiological findings can guide suspicion towards the diagnosis; however, in our current practice most diagnoses are based on histological findings. We aim to present a pararenal sclerosing perivascular epithelioid cell tumour (PEComa), a rare entity, whose diagnosis is only possible through invasive approaches and histological analysis. This rare lesion not only is difficult to diagnose but also has an uncertain behaviour, which is of major importance concerning its follow-up and prognosis. This case report is an attempt to add more data that will help establish criteria for diagnosis and follow-up of this rare disease.

Primary perivascular epithelioid cell tumor in the rectum: a case report and review of the literature

Perivascular epithelioid cell tumor (PEComa) is a rare collection of tumors arising in a wide array of anatomic locations. It is characterized by the presence of a peculiar population of myomelanocytic marker-positive perivascular epithelioid cells, and is commonly detected in the uterus. The colorectal area is an uncommon site for primary PEComa. In this study, we describe a 17-year-old patient presenting with a rectal polyp. Histologically, the tumor consisted of sheets of round to polygonal epithelioid cells with clear and granular cytoplasm, and a prominent capillary network. Some of the tumor cells were positive for Fontana-Masson staining. Immunohistochemically, the tumor cells were positive for HMB-45, and were negative for cytokeratin, vimentin, S-100 protein, actin, desmin, EMA, CD34, and c-kit. After finding melanosomes or premelanosomes at the ultrastructural level, the diagnosis of PEComa was made. Although PEComa arising within the intestinal tract is unusual and clinically unexpected, PEComa should be considered in the differential diagnosis of rectal polypoid lesions.

Perivascular epithelioid cell neoplasm of the urinary bladder in an adolescent: a case report and review of the literature

Abstract

Perivascular epithelioid cell neoplasms (PEComas) of the urinary bladder are extremely rare and the published cases were comprised predominantly of middle-aged patients. Herein, the authors present the first urinary bladder PEComa occurring in an adolescent. This 16-year-old Chinese girl present with a 3-year history of abdominal discomfort and a solid mass was documented in the urinary bladder by ultrasonography. Two years later, at the age of 18, the patient underwent transurethral resection of the bladder tumor. Microscopically, the tumor was composed of spindled cells mixed with epithelioid cells. Immunohistochemically, the tumor were strongly positive for HMB45, smooth muscle actin, muscle-specific actin, and H-caldesmon. Fluorescence in situ hybridization analysis revealed no evidence of EWSR1 gene rearrangement. The patient had been in a good status without evidence of recurrence 13 months after surgery. Urinary bladder PEComa is an extremely rare neoplasm and seems occur predominantly in middle-aged patients. However, this peculiar lesion can develop in pediatric population and therefore it should be rigorously distinguished from their mimickers.

Virtual slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1870004378817301

Microscopic endometrial perivascular epithelioid cell nodules: a case report with the earliest presentation of a uterine perivascular epithelioid cell tumor

Abstract

Perivascular epithelioid cell (PEC) tumors (PEComas) are a family of related mesenchymal tumors composed of PECs which co-express melanocytic and smooth muscle markers. Although their distinctive histologic, immunohistochemical, ultrastructural, and genetic features have been clearly demonstrated, their histogenesis and normal counterpart remain largely unknown. Precursor lesions of PEComas have rarely been reported. We herein describe a tuberous sclerosis patient with microscopic PEC nodules in the endometrium of adenomyosis, pelvic endometriosis, an ovarian endometriotic cyst, and the endometrium of the uterine cavity. The nodules showed a mixture of spindle-shaped and epithelioid cells concentrically arranged around small arteries. The cells exhibited uniform nuclei, light eosinophilic cytoplasm, and immunoreactivity with HMB-45 and CD10. Some nodules revealed continuity with a PEComa in the myometrium. These findings support microscopic endometrial PEC nodules possibly being precursor lesions of uterine PEComas. The wide distribution of the nodules in the pelvis may be related to the multicentricity of PEComas in tuberous sclerosis patients. Owing to the immunoreactivity with CD10, microscopic endometrial PEC nodules may be misinterpreted as endothelial stromal cells unless melanocytic markers are stained. To the best of our knowledge, this is a case with the earliest manifestation of PEC lesions occurring in the endometrium.

Virtual Slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/9658280017862643

Soft tissue tumors of uncertain origin

Many soft tissue tumors of childhood lack obvious differentiation toward a defined mesenchymal tissue type or have a phenotype that does not correspond to any defined normal tissue. These challenging tumors are currently regarded as neoplasms of uncertain differentiation. Nonetheless, there have been great strides in the understanding of their pathologic and genetic features and biologic underpinnings. The application of new genetic information to the pathologic diagnosis among this group of tumors is an emerging area in diagnostic pediatric pathology. This article reviews the clinicopathologic features of tumors of uncertain and/or miscellaneous origin, with an emphasis on the unique aspects of these neoplasms in children and adolescents, use of diagnostic adjuncts, and differential diagnosis.

"Malignant" perivascular epithelioid cell neoplasm: risk stratification and treatment strategies

Purpose. Perivascular epithelioid cell tumors (PEComas) are a rare collection of tumors characterized by a myomelanocytic phenotype, and PEComas occurring in “nonclassic” anatomic distributions are known as perivascular epithelioid cell tumor not otherwise specified (PEComa-NOS). This review aims to compile and analyze cases of PEComa-NOS in an effort to better define their natural history. Design. We evaluated all 234 cases of PEComa-NOS reported in the English literature, extracting information regarding diagnostic features, treatment approaches, and outcomes. Multivariate analysis of a number of variables evaluable on pathologic review was performed to refine preexisting risk stratification criteria. Outcomes for patients receiving nonsurgical treatment are also reported. Results. Primary tumor size ≥5 cm (P = 0.02) and a high (1/50 HPF) mitotic rate (P < 0.0001) were the only factors significantly associated with recurrence following surgical resection. Cytotoxic chemotherapy and radiation therapy have shown little benefit in treating PEComa-NOS; mTOR inhibition is emerging as a treatment option. Conclusion. Progress has been made in understanding the natural history and molecular biology of PEComa-NOS. This review further clarifies risk of recurrence in this disease, allowing clinicians to better risk stratify patients. Further work should focus on applying this knowledge to making treatment decisions for patients with this disease.

Bladder perivascular epithelioid cell tumor: a novel rare neoplasm

Perivascular epithelioid cell tumors (PEComas) have recently been defined as a group of neoplasms that have in common the co-expression of melanocytic and smooth muscle markers. We report a novel case of a rare bladder PEComa and we review the relevant literature.

Primary perivascular epithelioid cell tumor of the bladder

The perivascular epithelioid cell family of tumors includes angiomyolipoma, clear cell "sugar" tumor of the lung, lymphangioleiomyomatosis, and clear cell myomelanocytic tumor of the falciform ligament/ligamentum teres. Less frequently, perivascular epithelioid cell tumors arise in various other locations throughout the body including soft tissue, bone, and visceral organs. We report a case of a 23-year-old man who presented with 2-month history of frequent micturition and odynuria. Based on clinical examination, ultrasound computed tomography imaging, surgical operation, and histopathologic studies, a definitive diagnosis was made. Further characteristic images and pathology of this disease are discussed.

Perivascular epithelioid cell tumor of abdominal origin

Perivascular epithelioid tumor is not a common disease; therefore, large series are not available in the literature, and most are case reports. Histologic characteristics of these neoplasms are positivity to melanogenic (HMB-45) and muscle stains. All these neoplasms have the characteristic perivascular epithelioid cell or "PEC," but the term myomelanocyte tumor has been proposed because of the immunohistochemistry expression. Females are affected more commonly than males. The uterus seems to be one of the most common organs affected. Its clinical behavior is uncertain, and standard treatment has not been established as well as criteria for malignancy. We report 3 cases of abdominal PEComa, 1 of them with benign clinical outcome and 2 with an aggressive behavior.

PEComas: a review with emphasis on cutaneous lesions

The connection between angiomyolipoma (AML) of the kidney, clear cell sugar tumor (CCST) of the lung, and pulmonary lymphangioleiomyoma (LAM), was progressively discovered because of the histologic and immunophenotypic similarities between the three tumors and their frequent association with tuberous sclerosis complex (TSC). Morphologically, analogous lesions found in other locations are composed of the unifying cell, the perivascular epithelioid cell (PEC). PEC tumors (or PEComas), other than AML, CCST, and LAM, are not associated with TSC and typically occur in middle-aged adult females. These neoplasms are composed of nests and fascicles of clear to granular epithelioid and/or spindled cells with a consistent arrangement around blood vessels. Characteristically, the cells express both melanocytic (usually HMB45) and myogenic (typically actin) markers. Although the most common sites are the gastrointestinal and genitourinary tracts, approximately 23 cases, to date, of PEComas arising in the skin have been reported. Primary cutaneous PEComas also have a predilection for adult females and most often present as a painless mass on the extremities. In contrast to other sites, the myogenic marker most commonly expressed in PEComas of the skin is desmin. Most reported cutaneous PEComas follow a benign course, however, a malignant case has been reported. Surgical excision is currently the mainstay of treatment.

Perivascular epithelioid cell neoplasms: pathology and pathogenesis

This review article summarizes our current understanding of the clinical, pathologic, immunohistochemical, and genetic aspects of perivascular epithelioid cell neoplasms, a rare group of related tumors defined by both morphologic and immunophenotypic criteria.

Perivascular epithelioid cell neoplasms: a systematic review of prognostic factors

Perivascular epithelioid cell tumors (PEComas) are rare, soft tissue tumors characterized by epithelioid cells with clear or eosinophilic cytoplasm and a perivascular disbursement. We compiled the treatment and follow-up results from an extensive collection of reported gynecologic PEComa cases and statistically analyzed their respective therapy modalities and corresponding patient outcomes. In the group of patients with PEComa who received surgical management alone, there was a tendency for them to exhibit a lower disease recurrence rate. Conversely, patients with PEComa who initially received surgery and chemotherapy or radiation therapy were associated with a higher disease recurrence rate (P =.024). Metastatic involvement was related to higher patient mortality rates (P =.0001), although this finding was unrelated to treatment type. Surgical management alone may suffice for nonaggressive lesions, but chemotherapy and radiotherapy appear necessary for patients who present with high-risk histologic condition or metastatic disease. Because PEComas exhibit varying biologic behavior and an ill-defined presentation, the treatment for these lesions necessitates further evaluation.

Perivascular epithelioid cell tumor

Perivascular epithelioid cell tumors are mesenchymal neoplasms defined by the presence of histologically and immunohistochemically distinctive perivascular epithelioid cells. The perivascular epithelioid cell has no known normal tissue counterpart and coexpresses myoid and melanocytic markers. This tumor family shows marked female predominance and includes angiomyolipoma, clear cell sugar tumor, lymphangioleiomyomatosis, and a group of rare, morphologically and immunophenotypically similar tumors arising at a variety of visceral and soft tissue sites. This latter subset has been collectively termed perivascular epithelioid cell tumors-not otherwise specified. They are usually composed of epithelioid, but occasionally spindled, cells with clear to granular eosinophilic cytoplasm and focal perivascular accentuation. The mainstay of treatment is wide excision. Although most cases are benign, a subset behaves in a malignant fashion. Since few malignant cases have been reported, firm criteria for malignancy have yet to be established. This review focuses on the perivascular epithelioid cell tumors-not otherwise specified subset.

Polypoid PEComa in the rectum of a 15-year-old girl: case report and review of PEComa in the gastrointestinal tract

PEComa of the gastrointestinal tract, composed of perivascular epithelioid cells with myomelanocytic differentiation, is rare with previous literature limited to 16 case reports. There is a marked female preponderance and approximately one-third of the cases occur in the pediatric age group. We report PEComa with lymph node involvement occurring in the rectum of a 15-year-old girl, treated by surgical resection and adjuvant chemotherapy. The patient is well at 9 months follow-up with neither radiologic nor endoscopic evidence of recurrence. We review the differential diagnosis of intestinal PEComa, which includes malignant melanoma, epithelioid gastrointestinal stromal tumors, clear cell sarcoma of soft parts, alveolar soft part sarcoma, leiomyosarcoma with HMB45 expression, and paraganglioma. Immunohistochemistry can rule out many of these morphologically similar tumors but differentiation from clear cell sarcoma may require reverse transcription-polymerase chain reaction. We discuss the determination of pathologic features indicative of malignancy in PEComa, which is complicated in the gastrointestinal tract due to the small number of cases, variability of pathologic features reported, and inconsistent reporting of outcome. All 4 tumors reporting early recurrence or progression were greater than 5 cm in size and had areas of coagulative tumor necrosis. In addition, high nuclear grade and lymphovascular invasion were seen in 2 of these 4 cases. We propose that a minimum dataset for gastrointestinal PEComa should include these features along with mitotic count, infiltrative border, and tumor stage analogous to that used in colorectal carcinoma.

Perivascular epithelioid cell tumor of the rib

We present a rare case of perivascular epithelioid cell tumor (PEComa) in the right 6th rib of a 28-year-old man. A plain computed tomography scan showed a round osteolytic lesion in the right 6th rib. The resected tissue contained a globular-shaped, soft tumor. Histologically, the tumor was rich in vasculature and exclusively composed of perivascular epithelioid cells with clear cytoplasm. Immunohistochemically, the tumor expressed diffusely a melanocyte marker, human melanoma black-45, and focally a myogenic marker, alpha-smooth muscle actin, but not an epithelial marker, AE1/AE3. Fontana-Masson-positive melanin pigments were present and c-kit receptor tyrosine kinase (CD117), involved in the development of melanocytes but not myogenic cells, was expressed in tumor cells. These findings indicate that the tumor is PEComa with some differentiation into melanocytes. Notably, owing to the unique location of the occurrence, the tumor occupied bone marrow tissues of the rib, resulting that the tumor has the potential for hematogenous metastasis. In spite of the lack of cells with severe atypia, necrosis, and numerous mitoses, tumor cells invaded into surrounding tissues and overexpressed cyclin D1. To the best of our knowledge, this is the first case report of PEComa arising from the rib with the signs of malignant potential.

Perivascular epithelioid cell tumor (PEComa) of the uterus: an outcome-based clinicopathologic analysis of 41 reported cases

The uterus and retroperitoneum have emerged as the most frequently reported anatomic sites of origin of perivascular epithelioid cell tumors (PEComas), a poorly defined neoplasm that is characterized by varying amounts of spindle and epithelioid cells with clear to eosinophilic cytoplasm that display immunoreactivity for melanocytic markers, most frequently HMB-45. Published reports on 41 previously reported uterine PEComas are reviewed in this report. Of these 41 cases, 31 originating in the corpus and for which there was adequate follow-up information (or clinical malignancy) were categorized into 2 groups: (1) a malignant group that was comprised of cases associated with patient death of disease and/or clinical malignancy as evidenced by local and/or distant extension outside of the uterus (n=13, group 1) and (2) a "nonmalignant" group of cases in which neither of the above features were present (n=18, group 2). Groups 1 and 2 did not significantly differ regarding duration of follow-up (25 mo vs. 24.3 mo, respectively, P=0.9) or patient age (45.61 y vs. 43.46 y, respectively, P=0.7). Five of the group 1 patients experienced distant (extra-abdominal) metastases. The group 1 tumors were significantly larger than the group 2 tumors (averages 9.6 cm vs. 4.67 cm respectively, P=0.04); however, there were no size thresholds that, in of themselves, reliably classified 75% or more of the cases in both groups. Coagulative necrosis was highly associated with group 1, being present in 82% of cases as compared with only 11.8% of group 2 cases (P=0.0002). Eighty-eight percent of the group 2 cases had a mitotic rate of <or=1/10 high power fields (HPF) as compared with 40% of group 1 cases (P=0.01). However, the absence of mitotic activity did not rule out malignancy, as 2 of the group 1 cases lacked mitotic activity and displayed metastases. Twenty-five percent, 49%, 56%, 73%, and 100% of tested cases displayed immunoreactivity for CD10, desmin, vimentin, smooth muscle actin, and caldesmon, respectively. PEComas are tumors of uncertain histogenesis and malignant potential that seem to display some morphologic and immunophenotypic overlap with smooth muscle neoplasia. A mitotic count of >1/10 HPF and/or coagulative necrosis are features that, if present, raise the definite potential for aggressive behavior.

PEComas: the past, the present and the future

The perivascular epithelioid cell (PEC) is a cell type constantly present in a group of tumors called PEComas. PEC expresses myogenic and melanocytic markers, such as HMB45 and actin. Recently, recurrent chromosomal alterations have been demonstrated in PEC. At present, PEComa is a widely accepted entity. In the past 10 years, the use of this term has allowed to report and describe numerous cases permitting to start highlighting the biology of this group of lesions. PEComas are related to the genetic alterations of tuberous sclerosis complex (TSC), an autosomal dominant genetic disease due to losses of TSC1 (9q34) or TSC2 (16p13.3) genes which seem to have a role in the regulation of the Rheb/mTOR/p70S6K pathway. There are some open questions about PEComas regarding its histogenesis, the definition of epithelioid angiomyolipoma and the identification of the histological criteria of malignancy. An innovative therapeutic trial using rapamycin is under way for tumors occurring in TSC such as renal angiomyolipoma and lymphangioleiomyomatosis. Its success could provide the rationale for the use of the same drug in other lesions composed of PECs, especially in the malignant ones.