Uterine Perivascular Epithelioid Cell Tumor Research Articles

Clinical and ultrasound features of uterine perivascular epithelioid cell tumors: case series and literature review.

To describe the clinical and ultrasonographic features of uterine perivascular epithelioid cell tumor (PEComa) using standardized terminology. This was a retrospective analysis of patients with uterine PEComa diagnosed and confirmed by pathology and immunohistochemistry at West China Second University Hospital, Sichuan University, Sichuan, China, between January 2010 and September 2023. The Morphological Uterus Sonographic Assessment (MUSA) consensus and the International Endometrial Tumor Analysis (IETA) consensus were utilized for the standardized description of the sonographic characteristics of uterine PEComa. We summarized the clinical and ultrasound features of uterine PEComa in cases from our center and those found in a review of the literature conducted using PubMed from 1 January 2013 to 30 September 2023 (inclusive). Five patients, aged 33-57 (median, 52) years with a total of six uterine PEComa lesions were included in our cohort. All cases had complete ultrasonographic and pathological images. None of the patients had a history of tuberous sclerosis complex. Two patients had malignant PEComa (one patient had two lesions) and three had benign PEComa, originating from the cervix, myometrium or uterine cavity. Patients presented with symptoms including increased vaginal discharge, vaginal bleeding and pelvic or abdominal pain. The three patients with benign PEComa underwent total hysterectomy and bilateral adnexectomy, tumor excision and conservative management, respectively, while both malignant cases underwent total hysterectomy and bilateral adnexectomy followed by chemotherapy. Regular follow-up (from 6 to 24 months) revealed recurrence in one case. Two lesions were misdiagnosed as uterine fibroids, two as cervical cancer, one as metastatic cervical cancer (with myometrial invasion) and one was indeterminate. Ultrasound examination showed that most lesions displayed regular round or ovoid shapes (66.7%), uniform echoes (66.7%) and hypoechogenicity (66.7%), with one (16.7%) malignant PEComa showing cystic areas and one (16.7%) benign PEComa showing punctate calcifications. All lesions lacked shadowing and the majority showed moderate to abundant vascularity (color score of 3-4, 83.3%). The color score was 2-4 in the periphery in 100% of cases and internally in 83.3% of cases. The three benign PEComas showed similar characteristics in vascular distribution, with scattered internal vessels and peripheral vessels exhibiting a circular pattern. The literature search identified 11 articles describing the ultrasonographic appearance of 18 cases of uterine PEComa, with similar characteristics to those in our cohort. The sonographic features of uterine PEComa include a uniform or non-uniform hypoechogenic mass, typically round or ovoid with regular margins, occasionally containing cystic areas or calcifications, lacking shadowing and often showing moderate to abundant vascularity. Although the preoperative ultrasound diagnosis of uterine PEComa remains challenging, particularly given the non-specific nature of the sonographic characteristics described here, dispersed intratumoral vessels and a peripheral circular vascular distribution may serve as diagnostic clues for uterine PEComa, but more cases are needed for confirmation. © 2024 International Society of Ultrasound in Obstetrics and Gynecology.

Conservative treatment in uterine perivascular epithelioid cell tumor of uncertain malignant potential: a case report

IntroductionPerivascular epithelioid cell tumors are uncommon mesenchymal tumors. The genital tract is the most common extrarenal location. Preoperative diagnosis is rarely achieved owing to non-specific symptoms and imaging features. Consensus on treatment strategies remains elusive.Case presentationWe report the case a 38 year-old north African woman with a primary sterility, who was diagnosed with a uterine Perivascular epithelioid cell tumor of uncertain malignant potential on a resection specimen of an intracavity polypoid mass. Immunohistochemistry confirmed the diagnosis and we opted for conservative surgery to preserve the patient’s fertility desires.ConclusionUterine perivascular epithelioid cell tumor is a rare entity that warrants consideration in the differential diagnosis of uterine tumors. Treatment modalities, follow-up protocols, and prognosis remain ambiguous. Given their unpredictable behavior, accurate diagnosis and long-term monitoring are imperative.

TSC2-mutant uterine sarcomas with JAZF1-SUZ12 fusions demonstrate hybrid features of endometrial stromal sarcoma and PEComa and are responsive to mTOR inhibition

Uterine perivascular epithelioid cell tumor (PEComa) is a rare mesenchymal neoplasm that occasionally shares morphologic and immunohistochemical overlap with low- and high-grade endometrial stromal sarcoma (LGESS and HGESS). In this study, we sought to characterize the clinical, morphologic, genetic, and epigenetic features of five uterine sarcomas that display histologic features of LGESS, HGESS, and PEComa. All tumors demonstrated epithelioid cells often associated with a low-grade spindled component resembling LGESS, with both regions expressing CD10, ER, PR, variable HMB45, and Melan-A immunoreactivity, and strong cathepsin K and pS6 expression. Targeted massively parallel sequencing analysis revealed the presence of somatic TSC2 mutations in all five cases, of which four harbored concurrent or consecutive JAZF1-SUZ12 gene fusions. Unsupervised hierarchical clustering analysis of methylation profiles of TSC2-mutant uterine sarcomas (n = 4), LGESS (n = 10), and HGESS (n = 12) demonstrated two clusters consisting of (1) all LGESS and TSC2-mutant uterine sarcomas and (2) all HGESS. KEGG pathway analysis detected methylation differences in genes involved in PI3K/AKT, calcium, and Rap1 signaling. TSC2-mutant uterine sarcomas were responsive to hormone suppression, and mTOR inhibition demonstrated clinical benefit in four patients with these neoplasms. Our results suggest that these tumors represent histologically distinctive LGESS with TSC2 mutations. TSC2 mutations and JAZF1-SUZ12 fusion may help diagnose these tumors and possibly direct effective treatment.

Uterine Perivascular Epithelioid Cell Tumor Diagnostic Differences Between Endometrial Curettage Material and Resection Material and Histopathological and Immunohistochemical Approach to the Difficulties in Differential Diagnosis

Uterine perivascular epithelioid cell tumor is a rare mesenchymal tumor consisting of histologically and immunohistochemically distinctive perivascular epithelioid cells. These tumors’ being rare, having different morphological features and having similar immunohistochemical expression findings to that of some tumors lead to diagnostic difficulties and misdiagnoses. In the present case report, we aimed to discuss the traps we fell into while diagnosing the curettage material as neuroendocrine tumor and how we have been directed to the diagnosis of perivascular epithelioid cell tumor, as well as to discuss what to be taken into account while making the differential diagnosis under the guidance of the literature.

VEGFR Inhibitors for Uterine Metastatic Perivascular Epithelioid Tumors (PEComa) Resistant to mTOR Inhibitors. A Case Report and Review of Literature.

Uterine perivascular epithelioid cell tumors (PEComas) are rare neoplasms. PI3K/AKT/mTOR pathway upregulation is critical for their pathogenesis and is often associated with TSC1/TSC2 inactivation. Although first line mTOR inhibitors are an effective treatment, metastatic PEComas eventually progress. A 53-year-old woman presented a 4-month history of post-menopausal vaginal bleeding. Clinical and radiological examination detected a uterine mass and a single S1 bone lesion. The patient underwent a radical hysterectomy and bone biopsy. The anatomopathological evaluation concluded to an oligo-metastatic uterine PEComa. The tumor harbored a heterozygous deletion of 9q34 that contains the TSC1 gene. Concerning the primary lesion, the resection was complete and the single bone metastasis was treated with radiotherapy. Three months later, the patient presented bone, lung and subcutaneous metastatic progression. An everolimus and denosumab treatment was initiated. After 2 years of treatment, a clinically significant bone, lung and subcutaneous progression was detected. Following a literature review of the possible therapeutic options, we initiated a second line treatment by pazopanib. This treatment resulted in regression of the subcutaneous lesions and stability of lung and bone metastases. In this challenging, rare setting, our report suggests single agent, anti-angiogenic, tyrosine kinase inhibitor to be effective as second line treatment of metastatic uterine PEComa progressing on mTOR inhibitors.

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.

Uterine PEComas: A Morphologic, Immunohistochemical, and Molecular Analysis of 32 Tumors.

Uterine perivascular epithelioid cell tumors (PEComas) are rare neoplasms that may show overlapping morphology and immunohistochemistry with uterine smooth muscle tumors. In this study, we evaluated the morphologic, immunohistochemical, and molecular features of 32 PEComas, including 11 with aggressive behavior. Two distinct morphologies were observed: classic (n=30) and those with a lymphangioleiomyomatosis appearance (n=2). In the former, patients ranged from 32 to 77 (mean: 51) years and 13% had tuberous sclerosis. Tumors ranged from 0.2 to 17 (mean: 5.5) cm with 77% arising in the corpus. Epithelioid cells were present in 100% and a spindled component was seen in 37%. Nuclear atypia was low (53%), intermediate (17%), or high (30%). Mitoses ranged from 0 to 36 (mean: 6) and 0 to 133 (mean: 19) per 10 and 50 high-power fields, with atypical mitoses present in 30%. Thin and delicate vessels were noted in 100%, clear/eosinophilic and granular cytoplasm in 93%, stromal hyalinization in 73%, necrosis in 30%, and lymphovascular invasion in 10%. All tumors were positive for HMB-45, cathepsin K, and at least one muscle marker, with most expressing melan-A (77%) and/or MiTF (79%). A PSF-TFE3 fusion was identified in one while another showed a RAD51B-OPHN1 fusion. Follow-up ranged from 2 to 175 (mean: 41) months, with 63% of patients alive and well, 20% dead of disease, 13% alive with disease, and 3% dead from other causes. In the latter group (n=2), patients were 39 and 49 years old, one had tuberous sclerosis, while the other had pulmonary lymphangioleiomyomatosis. Both tumors expressed HMB-45, cathepsin K, and muscle markers, but lacked TFE3 and RAD51B rearrangements. The 2 patients are currently alive and well. Application of gynecologic-specific criteria (≥4 features required for malignancy: size ≥5 cm, high-grade atypia, mitoses >1/50 high-power fields, necrosis, and lymphovascular invasion) for predicting outcome misclassified 36% (4/11) of aggressive tumors; thus, a modified algorithm with a threshold of 3 of these features is recommended to classify a PEComa as malignant.

Predicting the Behavior of Perivascular Epithelioid Cell Tumors of the Uterine Corpus

Perivascular epithelioid cell tumors (PEComas) are rare neoplasms that share phenotypic features with angiomyolipomas, clear cell sugar tumors, and lymphangioleiomyomatosis. They presumably represent the neoplastic counterpart of a yet-unidentified perivascular epithelioid cell that expresses smooth muscle and melanocytic immunomarkers. The uterus is the second most common site of origin for perivascular epithelioid cell tumors, after the retroperitoneum. Although most uterine perivascular epithelioid cell tumors are clinically benign and can be cured by a complete surgical excision, there is a subset characterized by both local and distant dissemination. Unfortunately, no single histopathologic or immunohistochemical parameter can accurately predict the clinical behavior of these tumors, which is why the 2012 World Health Organization classification of tumors of the female reproductive organs suggests the use of several criteria to predict the risk of aggressive clinical behavior. Here we review those perivascular epithelioid cell tumors of the uterine corpus with aggressive clinical behavior reported in the literature, and we discuss their most relevant clinical and histopathologic features.

Incidental Pelvic and Para-aortic Lymph Node Lymphangioleiomyomatosis Detected During Surgical Staging of Pelvic Cancer in Women Without Symptomatic Pulmonary Lymphangioleiomyomatosis or Tuberous Sclerosis Complex.

Extrapulmonary lymphangioleiomyomatosis (LAM) is a rare neoplasm of spindle cells exhibiting melanocytic and myoid differentiation that arises as a mass in the mediastinum, retroperitoneum, uterine wall, and/or intraperitoneal lymph nodes. Many patients also have pulmonary LAM, tuberous sclerosis complex (TSC), and/or other neoplasms of the perivascular epithelioid cell tumor family. This study reports 26 patients with clinically occult LAM involving pelvic/para-aortic lymph nodes removed from women undergoing surgical staging of a uterine (17), ovarian (5), cervical (3), or urinary bladder (1) neoplasm. None of the patients exhibited symptoms of pulmonary LAM, and the median patient age (56 y) was older than what would be expected for patients presenting with pulmonary LAM. Only 2/26 patients had TSC. Four patients also had uterine LAM. One of these 4 had uterine perivascular epithelioid cell tumor, and 1 had vaginal angiomyolipoma. In all 26 patients the lymph node LAM was grossly occult, measured 3.5 mm on average (1 to 19 mm), and involved either a single lymph node (12/26) or multiple lymph nodes (14/26). HMB45 was positive in 24/25 cases, mostly in a focal or patchy distribution. Other melanocytic markers included MiTF (12/14) and MelanA (2/12). Myoid markers included smooth muscle actin (23/23) and desmin (15/16), mostly in a diffuse distribution. Estrogen receptor was positive in all cases tested, as was D240 expression in the lymphatic endothelium lining the spindle cell bundles. Concurrent findings in the involved lymph nodes included metastatic carcinoma (3/26), endosalpingiosis (3/26), and reactive lymphoid hyperplasia (13/26). This study demonstrates that clinically occult lymph node LAM can be detected during surgical staging of pelvic cancer and is not commonly associated with pulmonary LAM or TSC, although these patients should still be formally evaluated for both of these diseases.

Fertility sparing treatment of a malignant uterine perivascular epithelioid cell tumor: A case report

•Perivascular epithelioid cell tumors (PEComas) are a family of rare, poorly defined mesenchymal tumors of uncertain malignant potential.•Treatment for PEComas has most commonly involved excisional biopsy or surgical resection.•The use of mTOR inhibitors may provide the best medical treatment as well as a fertility-sparing treatment option.

Trends in the Prevalence of Tuberous Sclerosis Complex Manifestations: An Epidemiological Study of 166 Japanese Patients

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder with multi-system involvement and variable manifestations. There has been significant progress in TSC research and the development of technologies used to diagnose this disorder. As a result, individuals with mild TSC are now being diagnosed, including many older adults who have not developed seizures or cognitive abnormalities. We conducted a statistical analysis of the frequency of TSC manifestations in a population of Japanese adults and children, comparing our findings with historical data. The chi-square test was used to examine the frequency of each manifestation by age. A total of 166 outpatients at the Department of Dermatology of Osaka University Hospital during the period from January 2001 to March 2011 were included in the study. Compared to previous reports, the frequency of neurologic manifestations (excepting autism) was lower in this cohort, and the frequency of skin manifestations (excepting hypomelanotic macules) was higher in this cohort. The frequencies of pulmonary lymphangioleiomyomatosis and renal manifestations were not significantly different from those previously reported. Regarding the association of each manifestation with age, the frequency of neurologic manifestations (excepting subependymal giant cell astrocytoma) was significantly higher in younger patients than in older patients. The frequency of skin manifestations and renal angiomyolipoma were significantly higher in older patients than in younger patients. Because of their high frequency and visibility, skin manifestations are useful in the diagnosis of TSC. Moreover, uterine perivascular epithelioid cell tumor was also characterized as a new findings associated with TSC.

Endometrial stromal sarcoma complicating uterine perivascular epithelioid cell tumor: report of a case

患者女,43岁.因无明显诱因出现下腹部间断性刀割样疼痛,伴腹胀、下坠感1周来本院就诊,曾于2011年12月初当地医院B超示:子宫增大,多发肌瘤,于2011年12月收入本院.妇科检查:子宫前位,如孕5个月大小,可触及多个大小不等的凸起,质硬,活动度差,压痛阳性。

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

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

Malignant Perivascular Epithelioid Cell Tumor (PEComa) of the Uterus

Abstract: This is a case of a 52-year-old woman who underwent a hyster-ectomy to treat a large uterine perivascular epithelioid cell tumor. She wasfollowed with serial F-18 FDG PET/CT scans due to positive surgicalmargins and vascular invasion on pathology. Initial surveillance PET/CTperformed 6 months post surgery was negative; however, a second surveil-lance PET/CT performed 12 months post surgery showed an intenselyFDG-avid recurrence in the pelvic surgical site. The patient received localradiotherapy, 2 cycles of taxol and carboplatin, and was placed on imatinibmesylate (Gleevec). A final PET/CT performed 6 months after initiation oftherapy showed rapidly disseminating metastatic disease and the patient died1 month later. This rare report highlights a potentially new utility of F-18FDG PET/CT for surveillance of recurrence of a malignant uterine perivas-cular epithelioid cell tumor, as well as for evaluation of response to therapy. Key Words: malignant perivascular epithelioid cell tumor, PEComa,uterus tumors, FDG, PET/CT(

Fertility-sparing operation for recurrence of uterine cervical perivascular epithelioid cell tumor

Fertility-sparing operation for recurrence of uterine cervical perivascular epithelioid cell tumor

Epithelioid smooth muscle tumors of the uterus do not express CD1a: a potential immunohistochemical adjunct in their distinction from uterine perivascular epithelioid cell tumors

Uterine epithelioid smooth muscle tumors and uterine perivascular epithelioid cell tumors (PEComas) are known to display such a substantial overlap in morphologic and immunophenotypic characteristics that the existence of the latter as a distinct clinicopathologic entity at this location has been called into question. Recent research suggests that the constituent entities of the PEComa family at all anatomical locations, including lymphangioleiomyomatosis of the uterus, uniformly display immunoreactivity for CD1a. The purpose of this study is to determine the proportion of uterine epithelioid smooth muscle tumors that may similarly be CD1a-positive. Representative sections from 18 archived epithelioid smooth muscle tumors of the uterine corpus (6 epithelioid leiomyosarcomas and 12 epithelioid leiomyomas), diagnosed and classified as such based on World Health Organization criteria, were subjected to immunohistochemical stains for CD1a and HMB-45. The epithelioid component of the tissue sections evaluated ranged from 10% to 100% (mean, 70%). Two cases were composed predominantly of cells with overtly clear cytoplasm. All cases were entirely negative for CD1a. Of 18 cases, 1 (5.5%) (an epithelioid leiomyosarcoma) displayed immunoreactivity for HMB-45 in scattered lesional cells that constituted approximately 5% of the overall tumoral volume for the case. All others were HMB-45-negative. Given their rarity, future studies are required to confirm that all PEComas of the uterus are indeed uniformly positive for CD1a. However, if the latter staining pattern is confirmed, our findings herein suggest that CD1a may be a useful immunohistochemical adjunct in distinguishing uterine epithelioid smooth muscle tumors from uterine PEComas.

Uterine Perivascular Epithelioid Cell Tumor Coexisting With Pulmonary Lymphangioleiomyomatosis and Renal Angiomyolipoma

We present a case of uterine perivascular epithelioid cell tumor (PEComa) coexisting with both pulmonary lymphangioleiomyomatosis and renal angiomyolipoma. The patient was a 42-year-old woman, suffering from massive abnormal uterine bleeding, progressive dyspnea, and arterial hypertension. Her clinical history included diagnoses of bilateral renal angiomyolipoma and pulmonary lymphangioleiomyomatosis. The patient underwent a subtotal hysterectomy and the specimen contained a subserosal tumor with irregular outlines in addition to uterine leiomyomata. The uterine tumor was histologically composed of solid sheets and tonguelike infiltration and lymphangioleiomyomalike structures within the myometrium, formed by epithelioid cells with ovoid to round nuclei and clear to light eosinophilic cytoplasms. The tumor did not display any morphologic sign of malignancy. The tumor cells showed expression of HMB-45 and smooth muscle markers. Ultrastructural analysis revealed abundant cytoplasmic microfilaments and rare small cytoplasmic bodies with a gridlike lining. We conclude that identification of lymphangioleiomyomalike growth pattern may aid in the differential diagnosis of uterine PEComa and suggest using both PEComa and smooth muscle tumor terminology.

"Malignant" Uterine Perivascular Epithelioid Cell Tumor, Pelvic Lymph Node Lymphangioleiomyomatosis, and Gynecological Pecomatosis in a Patient With Tuberous Sclerosis

We report a case of uterine perivascular epithelioid cell tumor (PEComa) with malignant histological features in a 59-year-old woman with tuberous sclerosis (TBS). The patient also had extrapulmonary lymphangioleiomyomatosis involving pelvic lymph nodes, myometrium, cervix, and ovary ("pecomatosis"). The uterine tumor measured 2.6 cm and had marked nuclear pleomorphism, necrosis, and 2 mitoses per 50 high-powered field, with an occasional atypical mitosis and infiltrative borders. The nonneoplastic myometrium, the cervical wall, and the hilum of the ovary had multiple clusters of bland-looking epithelioid clear cells that ranged from 1 to 5 mm (pecomatosis). The uterine tumor cells were positive for HMB-45 (90%), Melan-A (70%), smooth muscle actin (50%), and estrogen receptor (30%). Of the 16 pelvic lymph nodes excised, 3 were involved with lymphangioleiomyomatosis that was positive for HMB-45 and estrogen receptor. This is only the second reported PEComa associated with pecomatosis and the fourth PEComa described in a patient with TBS. The clinical significance of pecomatosis is still uncertain but seems to be seen only in patients with TBS.

Perivascular Epithelioid Cell Tumor of the Uterus: Report of Four Cases

Uterine perivascular epithelioid cell tumor (PEComa) is very rare, and there have been only 27 reported cases. The differentiation of the tumor has been enigmatic, and the biologic behavior remains unclear. This study describes the clinical, histologic, and immunohistochemical features of four cases of uterine PEComa. The patients were 30, 32, 36, and 40 years old, and none of them had tuberous sclerosis complex. The size of the tumors ranged from 1 to 30 cm in diameter, and 3 of the 4 tumors were confined in the uterus. One tumor involved the left ovary and omentum. Microscopically, the tumors were characterized by an epithelioid arrangement of tumor cells, which had abundant clear to eosinophilic pale granular cytoplasm, and one tumor had moderately atypical nuclei. Coagulative necrosis was found in two cases. The mitotic figures ranged from 0 to 11 per 10 high power fields. Immunohistochemically, the tumors were positive for vimentin (4/4), HMB45 (4/4), h-caldesmon (4/4), alpha-smooth muscle actin (3/4), muscle actin (2/4), and desmin (3/4). They were uniformly negative for Melan A, CD10, and S-100 protein. Ultrastructural examinations were performed on one case and revealed no melanosomes, premelanosomes, or evidence of smooth muscle differentiation. One patient died of intestinal metastases 17 months after surgery. The other patients have been well with no evidence of disease 8, 12, and 36 months after surgery. Uterine PEComa should be regarded as tumors with an uncertain malignant potential until long-term outcome data for a larger number of patients become available.