Activation of the mTOR pathway in sporadic angiomyolipomas and other perivascular epithelioid cell neoplasms

Angiomyolipoma (AML) belong to a family of tumors known as perivascular epithelioid cell tumors (PEComas) that share a common immunophenotypic profile of muscle and melanocytic differentiation. These tumors are clonal in nature and have a strong association with tuberous sclerosis. Genetic analyses have reported allelic imbalance at the TSC2 locus on 16p13. In the context of non-tuberous sclerosis complex (TSC), non-lymphangioleiomyomatosis-associated AMLs, and non-renal PEComas, the functional status of the TSC2 signaling pathway has not been reported. Studies over the last several years have uncovered a critical role of the TSC1/2 genes in negatively regulating the Rheb/mTOR/p70S6K cascade. Here, we examined the activity of this pathway in sporadic AMLs and PEComas using immunohistochemical and biochemical analyses. We found increased levels of phospho-p70S6K, a marker of mTOR activity, in 15 of 15 non-TSC AMLs. This was accompanied by reduced phospho-AKT expression, a pattern that is consistent with the disruption of TSC1/2 function. Western blot analysis confirmed mTOR activation concurrent with the loss of TSC2 and not TSC1 in sporadic AMLs. Similarly, elevated phospho-p70S6K and reduced phospho-AKT expression was detected in 14 of 15 cases of extrarenal PEComas. These observations provide the first functional evidence that mTOR activation is common to sporadic, non-TSC-related AMLs and PEComas. This suggests the possibility that mTOR inhibitors such as rapamycin may be therapeutic for this class of disease.     

p53 in pure epithelioid PEComa: an immunohistochemistry study and gene mutation analysis

Pure epithelioid PEComa (PEP; so-called epithelioid angiomyolipoma) is rare and is more often associated with aggressive behaviors. The pathogenesis of PEP has been poorly understood. The authors studied p53 expression and gene mutation in PEPs by immunohistochemistry, single-strand conformation polymorphism, and direct sequencing in paraffin material from 8 PEPs. A group of classic angiomyolipomas (AMLs) were also analyzed for comparison. Five PEPs were from kidneys and 1 each from the heart, the liver, and the uterus. PEPs showed much stronger p53 nuclear staining (Allred score 6.4 ± 2.5) than the classic AML (2.3 ± 2.9) (P < .01). There was no p53 single-strand conformation polymorphism identified in either the PEPs or the 8 classic AMLs. p53 mutation analyses by direct sequencing of exons 5 to 9 showed 4 mutations in 3 of 8 PEPs but none in any of the 8 classic AMLs. The mutations included 2 missense mutations in a hepatic PEComa and 2 silent mutations in 2 renal PEPs. Both the missense mutations in the hepatic PEComa involved the exon 5, one involving codon 165, with change from CAG to CAC (coding amino acid changed from glutamine to histidine), and the other involving codon 182, with change from TGC to TAC (coding amino acid changed from cysteine to tyrosine). The finding of stronger p53 expression and mutations in epithelioid angiomyolipomas might have contributed to their less predictable behavior. However, the abnormal p53 expression cannot be entirely explained by p53 mutations in the exons examined in the PEPs.     

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.     

Late pulmonary metastasis in uterine PEComa

Perivascular epithelioid cell tumours (PEComas) other than angiomyolipoma, clear cell "sugar" tumour of the lung, and lymphangioleiomyomatosis are very rare mesenchymal tumours. The uterus seems to be the most prevalent site of involvement, but only 13 cases of uterine PEComa have been described. Three of these cases exhibited local aggressive behaviour and only one showed metastasis. Because of the extremely small number of cases, PEComas are considered tumours of uncertain malignant potential. This report describes a 68 year old woman, who presented with multiple pulmonary lesions seven years after the initial diagnosis of well differentiated endometrial stromal sarcoma. Histological and immunohistochemical analysis of the pulmonary lesions, in addition to re-evaluation of the primary uterine tumour, led to the final diagnosis of metastatic uterine PEComa. The findings indicate that any PEComa might have malignant potential. Spreading of this tumour to other organs might become evident even several years after primary manifestation.     

Malignant PEComa of the adrenal gland

Perivascular epithelioid cell neoplasms, also known as PEComas, are unique mesenchymal tumors exhibiting perivascular epithelioid cell differentiation, characterized by a mixed myogenic and melanocytic phenotype. PEComas arising in visceral organs outside of the kidney, liver, and lung are rare, and often pose problems in diagnosis. Examples of this neoplasm originating in the adrenal gland are limited. The present report details the clinical and pathologic features of an unusual case of a pure epithelioid PEComa (epithelioid angiomyolipoma) of the adrenal gland exhibiting clinically malignant behavior in the form of pulmonary metastases, a feature not previously described in tumors of this site. The diagnosis was supported by immunohistochemical studies demonstrating expression of myoid and melanocytic antigens. The present case serves to emphasize the potential of PEComa for clinically aggressive behavior and the importance of distinguishing this tumor from other epithelioid neoplasms that are more commonly encountered in the adrenal gland.     

Comparative genomic hybridization study of perivascular epithelioid cell tumor: molecular genetic evidence of perivascular epithelioid cell tumor as a distinctive neoplasm

Perivascular epithelioid cell tumor (PEComa) is a neoplasm composed chiefly of HMB-45-positive epithelioid cells with clear to granular cytoplasm and a perivascular distribution. Such tumors have been reported in different organs under a variety of designations. The cytogenetic features of these neoplasms have not been well studied. We collected 9 tumors (5 of kidney, 1 of prostate, 1 of urinary bladder, 1 of the pelvic cavity soft tissue, and 1 of uterus) from 8 patients, including one patient with tuberous sclerosis complex. The paraffin blocks of tumor tissue were submitted for comparative genomic hybridization analyses. Gross chromosomal aberrances were observed in all cases. The frequent imbalances were losses on chromosome 19 (8 cases), 16p (6 cases), 17p (6 cases), 1p (5 cases), and 18p (4 cases) and gains on chromosome X (6 cases), 12q (6 cases), 3q (5 cases), 5 (4 cases), and 2q (4 cases). The frequent deletion of 16p in which TSC2 gene is located indicates the oncogenetic relationship of PEComas with angiomyolipoma as a TSC2-linked neoplasm. From a molecular genetic perspective, the recurrent chromosomal alterations in both renal and extrarenal tumors further support the concept of PEComa as a distinctive tumor entity regardless of anatomic location.     

Frequent [corrected] hyperphosphorylation of ribosomal protein S6 [corrected] in lymphangioleiomyomatosis-associated angiomyolipomas.

Lymphangioleiomyomatosis is a progressive lung disease characterized by a diffuse proliferation of pulmonary smooth muscle cells and cystic degeneration. Lymphangioleiomyomatosis can occur either independently of other disease or in association with tuberous sclerosis complex, a tumor-suppressor gene syndrome caused by mutations that inactivate either TSC1 or TSC2. TSC2 mutations and loss of heterozygosity have been identified in sporadic lymphangioleiomyomatosis-associated angiomyolipomas, thus implicating the TSC/Ras homolog-enriched in brain (Rheb)/mammalian target of Rapamycin (mTOR)/p70 S6 kinase signaling pathway in their pathogenesis. This study was undertaken to determine whether the mTOR/p70 S6 kinase signaling pathway is activated in lymphangioleiomyomatosis-associated angiomyolipomas lacking TSC1/TSC2 loss of heterozygosity. Phospho-ribosomal protein S6 (Ser235/236) immunohistochemistry was performed on five lymphangioleiomyomatosis-associated angiomyolipomas, two matched lymphangioleiomyomatosis pulmonary samples, and three sporadic angiomyolipomas. TSC1/TSC2 loss of heterozygosity was previously excluded in these angiomyolipomas. Moderate or strong phospho-ribosomal protein S6 immunoreactivity was found in all lymphangioleiomyomatosis-associated and sporadic angiomyolipomas, suggesting a high incidence of mTOR/p70 S6 kinase signaling pathway activation despite a lack of TSC1/TSC2 loss of heterozygosity. Focally positive phospho-S6 staining was also evident in both lymphangioleiomyomatosis pulmonary samples. We hypothesized that this S6 hyperphosphorylation could reflect mutational activation of Rheb or Rheb-like protein (RhebL1), Ras family members which directly activate mTOR. Mutational analysis performed on DNA from these eight angiomyolipomas plus five additional sporadic angiomyolipomas did not reveal mutations in exons 3 and 4 (homologous sites of Ras activating mutations) of either Rheb or RhebL1. These data suggest that activation of the Rheb/mTOR/p70 S6 kinase pathway is related to the pathogenesis of lymphangioleiomyomatosis-associated and sporadic angiomyolipomas lacking TSC1/TSC2 loss of heterozygosity. This high incidence of mTOR signaling pathway activation suggests that treatment with mTOR inhibitors, such as Rapamycin, may benefit patients with angiomyolipomas independent of the detection of TSC1/TSC2 loss of heterozygosity.     

Perivascular epithelioid cell sarcoma (malignant PEComa) of the ileum

Epithelioid angiomyolipoma (AML) is the prototype of a heterogeneous group of lesions characterized by the presence of HMB-45 positive cells with clear cytoplasm, perivascular distribution, and combined myomelanocytic features, so-called perivascular epithelioid cells (PECs). These lesions are being increasingly referred to as PEComas. PEComas have been reported at diverse anatomic sites, but mainly in the abdominopelvic cavity and rarely in parenchymatous organs, skin, and soft tissues. Gastrointestinal (GI) PEComas are exceptionally rare, with less than 10 cases documented so far. Rare examples of PEComas with pleomorphic histology could have been misinterpreted as unusual variants of carcinoma or sarcoma. To make a contribution to the differential diagnosis of difficult-to-classify pleomorphic GI sarcomas, we report on a malignant pleomorphic neoplasm with features of PEComa involving the terminal ileum in a 63-year-old woman. Fourteen months after resection of the primary tumor, a huge abdominopelvic recurrence was successfully resected, but no distant metastases were detected. The differential diagnosis and malignancy criteria of GI PEComas will be discussed.     

Malignant neoplasm of perivascular epithelioid cells of the liver

Neoplasms of perivascular epithelioid cells (PEComas) have in common the coexpression of muscle and melanocytic immunohistochemical markers. Although this group includes entities with distinct clinical features, such as angiomyolipoma, clear cell sugar tumor of the lung, and lymphangioleiomyomatosis, similar tumors have been documented in an increasing diversity of locations. The term PEComa is now generally used in reference to these lesions that are not angiomyolipomas, clear cell sugar tumors, or lymphangioleiomyomatoses. While most reported PEComas have behaved in a benign fashion, malignant PEComas have occasionally been documented. We present a case of hepatic PEComa with benign histologic features, which nonetheless presented with metastases to multiple sites nearly 9 years later. This case represents the second documented malignant PEComa of the liver, as well as the longest follow-up of a surviving patient with a malignant PEComa, emphasizing both the need for criteria that more accurately predict the behavior of PEComas and the necessity of long-term follow-up of patients with PEComas.     

Loss of heterozygosity in the tuberous sclerosis (TSC2) region of chromosome band l6p13 occurs in sporadic as well as TSC-associated renal angiomyolipomas

Angiomyolipomas (AMLs) are renal tumors that occur both sporadically and in association with tuberous sclerosis (TSC). TSC is an autosomal dominant disorder characterized by hamartomatous lesions in multiple organs. Two TSC loci are recognized TSCl on 9q34 and TSC2 on 16pl3. Loss of heterozygosity (LOH) at the TSCI and TSC2 loci in lesions from TSC patients has recently been reported. Lesions that are not associated with TSC have not been previously examined for LOH at the TSC loci. We analyzed 29 renal angiomyolipomas from patients without a history of TSC. Three tumors demonstrated LOH on I6p 13. This is the first report indicating that mutations in TSC2 occur in tumors of patients who do not have TSC. We also found LOH on I6p 13 in 5 of 8 TSC-associated AMLs. Two of these tumors were from a single patient and demonstrated different regions of LOH. These findings support the hypothesis that the TSC2 gene functions as a tumor suppressor.     

Renal angiomyolipomas from patients with sporadic lymphangiomyomatosis contain both neoplastic and non-neoplastic vascular structures

Renal angiomyolipomas are highly vascular tumors that occur sporadically, in women with pulmonary lymphangiomyomatosis (LAM), and in tuberous sclerosis complex (TSC). The goal of this study was to determine whether the distinctive vessels of angiomyolipomas are neoplastic or reactive. We studied angiomyolipomas with loss of heterozygosity (LOH) in the TSC2 region of chromosome 16p13 from patients with LAM. We found that angiomyolipomas contain five morphologically distinct vessel types: cellular, collagenous, hemangiopericytic, glomeruloid, and aneurysmatic. Using laser capture microdissection, we determined that four of the vessel types have TSC2 LOH and are therefore neoplastic. One vessel type, collagenous vessels, did not have LOH, and is presumably reactive. Recently, activation of S6 Kinase and its target S6 ribosomal protein (S6) was demonstrated in cells lacking TSC2 expression. We found that angiomyolipoma vessel types in which LOH were detected were immunoreactive with anti-phospho-S6 antibodies. Angiomyolipoma cells without LOH, including the endothelial component of the vessels, were not immunoreactive. To our knowledge, angiomyolipomas are the first benign vascular tumor in which the vascular cells, rather than the stromal cells, have been found to be neoplastic. Angiomyolipomas appear to reflect novel vascular mechanisms that may be the result of activation of cellular pathways involving S6 Kinase.     

Perivascular epithelioid cell tumor (PEComa) of the liver: a case report and review of the literature

Perivascular epithelioid cell tumor (PEComa) is rare entity and has been described only recently. By immunohistochemistry and genetics it belongs to the family of tumours which comprises angiomyolipoma, clear cell "sugar" tumor of lung, lymphangioleiomyomatosis and clear cell myomelanotic tumor of ligamentum falciforme/teres hepatis. We describe an unusual case of hepatic PEComa arising in a 55-year-old woman with previous history of glioblastoma. Histologically the tumor grew in expansive way, and was composed of clear and eosinophilic epithelioid cels, without vascular or lipomatous component characteristic of angiomyolipoma. There was mild nuclear pleomorphism, sporadic mitotic activity and haemorrhage without necrosis. On immunohistochemistry, the tumor was HMB-45+50, Melan-A and smooth muscle actin positive. Tyrosinase, S-100 protein, cytokeratin coctail, EMA, vimentin, muscle specific actin, CD10, TTF-1, hepatocyte, desmin and cyclin D1 were negative. Sporadic nuclear p53 positivity was seen. The main differential diagnosis of hepatic PEComa includes clear cell variant of liver cell adenoma and hepatocellular carcinoma, metastases of various clear cell carcinomas and metastasis of malignant melanoma. In respect of uncertain biologic potential of PEComa, long term follow up is indicated.     

Colonic angiomyolipoma with a monotypic expression and a predominant epithelioid component

Angiomyolipomas are rare lesions, often arising in the kidney, and are part of a group of tumours with a diverse appearance and evidence of dual melanocytic and smooth muscle differentiation known as PEComas (tumours of perivascular epithelioid cell origin). This report describes an unusual case of a colonic PEComa in a 40 year old woman. Unlike most of the previous colonic angiomyolipomas/PEComas reported in the literature, this case formed a large, mainly extrinsic mass and was monotypic, and composed entirely of the myomatous component with no adipose tissue or typical vasculature.     

PEComa: what do we know so far?

PEComas (tumours showing perivascular epithelioid cell differentiation) are a family of related mesenchymal neoplasms that include angiomyolipoma, lymphangiomyomatosis, clear cell "sugar" tumour of the lung, and a group of rare, morphologically and immunophenotypically similar lesions arising at a variety of visceral and soft tissue sites. These tumours all share a distinctive cell type, the perivascular epithelioid cell or "PEC' (which has no known normal tissue counterpart). PEComas show a marked female predominance and are composed of nests and sheets of usually epithelioid but occasionally spindled cells with clear to granular eosinophilic cytoplasm and a focal association with blood vessel walls. PEComas appear to arise most commonly at visceral (especially gastrointestinal and uterine), retroperitoneal, and abdominopelvic sites, with a subset occurring in somatic soft tissue and skin. Nearly all PEComas show immunoreactivity for both melanocytic (HMB-45 and/or melan-A) and smooth muscle (actin and/or desmin) markers. A subset of PEComas behave in a malignant fashion. This review examines the members of the PEComa family, with an emphasis on lesions arising outside of the kidney, lung and liver, and discusses preliminary evidence for pathological features that might predict malignant behaviour.     

Pancreatic perivascular epithelioid cell tumor (PEComa)

Neoplasms with perivascular épithelioid-cell differentiation (PEComas) are rare tumors with a distinctive immunoreactivity for melanocytic markers. They have been described in various organs. We report an intrapancreatic PEComa discovered in a 46-year-old woman during a workup for diarrhea. CT scan showed a 1.7cm nodule in the body of the pancreas with slight-contrast enhancement at arterial time and isodense at portal time. The aspect was suggestive of an endocrine tumor despite negative somatostatin-receptor scintigraphy. Enucleation was performed. Pathologic evaluation showed a well-circumscribed intrapancreatic tumor consisting of a population of clear to eosinophilic spindle cells and a less abundant population of epithelioid cells arranged around blood vessels. Tumor cells expressed vimentin, HMB45 and actin and only focally S-100 protein, KL1, CD117 and CD34. These features were consistent with a PEComa. Pancreatic PEComas are rare, but should be included in the differential diagnostic of pancreatic clear cells tumors or pancreatic spindle- and epithelioid-cells tumors.     

Perivascular epithelioid cell tumour (PEComa) of the soft tissue

AIMS: PEComa is a rare tumour developing from perivascular epithelioid cells (PEC) and is characterised by positive immunoreactivity for HMB45. Since PEComas are tumours having both a spindle cell component and an epithelioid and giant cell component, as seen in many sarcomas, as well as having a wide distribution in various organs and soft tissue, we reviewed cases originally diagnosed as sarcomas of the soft tissue in our institution and screened them by immunostaining for HMB45. METHODS: Consecutive soft tissue sarcomas (31 tumours) retrieved from the Surgical Pathology file at our institution for a period of 3 years were submitted for immunostaining for HMB45. Cases with positive HMB45 immunostaining were submitted for further immunostaining for MART1, CD68, S100 protein, cytokeratin AE1/3, EMA, vimentin, MSA and CD117. RESULTS: Of 31 sarcomas, three tumours in the group of 11 malignant fibrous histiocytomas (MFH) and unclassified sarcomas showed positive immunoreactivity for HMB45 and MART1 in 1-25% of tumour cells. The three tumours were located in the lower extremities and measured 8, 11 and 12 cm in diameter. Patient gender male:female was 2:1 and ages were 46, 56 and 60 years. Microscopically, the tumours were composed of a variable proportion of spindled cells, multinucleated cells and epithelioid cells disposed in diffuse sheets or nests. Mitotic figures and necrosis were frequent. The immunoreactivity was diffuse for CD68, focal for AE3 and EMA, negative or focal for MSA and CD117, and negative for S100 and AE1. All three patients developed lymph node or distant metastases and died of the disease within 1-2 years. CONCLUSIONS: PEComa re-screened from the group of high grade sarcomas without definite differentiation range from pleomorphic to monomorphic cytohistopathological features. Immunostaining for HMB45 of unclassified sarcomas is useful for the classification of these tumours. They occur preferentially in the lower extremities and have a high malignant potential when associated with large size, tumoural necrosis and high mitotic activity.     

Uterine PEComa with aggressive behavior: A review with an additional case of spontaneous vaginal expulsion

Perivascular epithelioid cell tumor (PEComa) is a rare mesenchymal tumor originating from perivascular epitheloid cells showing melanocytic and smooth muscle differentiation. The uterus represents the second most common site of origin. A 49 years woman presented to our Hospital for a vaginal spontaneous expulsion of a mass suggestive for malignant mesenchymal tumor. The patient underwent total hysterectomy and bilateral salpingo-oophorectomy and the histopathological report was compliant with a PEComa with aggressive behavior. Medical Literature databases about PEComa were searched. The current literature identified near 90 cases of uterine PEComas and they are categorized as uncertain malignant potential or with aggressive behavior. Primary surgical excision represents the gold-standard treatment. Recently targeted therapy with mTOR inhibitors has been introduced with an important beneficial. In this paper we review the Literature about the uPEComa with aggressive behavior reporting the first case of spontaneous vaginal expulsion.     

Perivascular epithelioid cell tumor (PEComa) of the pancreas: Immunoelectron microscopy and review of the literature

A perivascular epithelioid tumor (PEComa) is a rare tumor probably arising from the perivascular epithelioid cells. Only three cases of pancreatic PEComa have been reported in the English-language literature. The present report describes an extremely rare case of pancreatic PEComa. A 47-year-old Japanese woman complained of lower abdominal pain and a well-demarcated solid tumor was found in the pancreatic head. There was no history of tuberous sclerosis complexes. Pylorus-preserving pancreaticoduodenectomy was thus performed. There was a well-demarcated, solid tumor measuring 17 mm in the pancreatic head. The tumor was composed of a diffuse proliferation of epithelioid tumor cells with many blood vessels but no adipose tissue. The tumor cells expressed HMB45 and α-smooth muscle actin. Ultrastructurally, the tumor cells possessed many membrane-bound granules that were positive for HMB45 on immunoelectron microscopy. The results of immunoelectron microscopy show that some PEComas possess not only typical melanosomes or premelanosomes but also aberrant melanosomes.     

A huge malignant perivascular epithelioid cell tumor (PEComa) of the uterine cervix and vagina

Perivascular epithelioid cell tumors (PEComas) are a family of rare mesenchymal neoplasms, including angiomyolipoma, clear-cell “sugar” tumor of the lung and extrapulmonary sites, lymphangioleiomyomatosis, clear-cell myomelanocytic tumor of the falciform ligament/ligamentum teres, and clear-cell tumors at various other anatomic sites.