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

Risk Stratification of Miscellaneous Uterine Mesenchymal Neoplasms: The Role of Morphology, Immunohistochemistry, and Molecular Testing

Uterine mesenchymal tumors are a diverse group of tumors that can display a broad range of morphologic, immunohistochemical, and molecular profiles and are associated with varied clinical behaviors. In recent years, they have increasingly been classified by their underlying molecular alterations, leading to a more precise separation of diagnostic entities. As their diagnostic criteria have been refined, so too have the features that can be used to predict clinical outcomes. This review includes a discussion of uterine inflammatory myofibroblastic tumors, perivascular epithelioid cell tumors (PEComa), and uterine tumors resembling ovarian sex cord tumors, with a focus on updates on their clinical behavior and tools for risk stratification to identify malignant tumors. In addition, we discuss the importance of using an integrated approach when classifying uterine mesenchymal tumors to improve diagnostic accuracy and guide clinical management.

Uterine Smooth Muscle Tumors: An Overview

Uterine smooth muscle tumors are a heterogeneous group of mesenchymal neoplasms with multiple histologic variants and distinct biological behaviors. Pathologic classification (benign, uncertain malignant potential, malignant) relies on the evaluation of mitotic index, necrosis, and degree of cytologic atypia, with different thresholds based on each subtype. Immunohistochemistry and other ancillary studies may be necessary to establish the diagnosis in a subset of cases, given the morphologic overlap with other mesenchymal neoplasms, including low-grade and high-grade endometrial stromal tumors, inflammatory myofibroblastic tumors, and PEComa. Recent advances in molecular diagnostics have refined the classification of smooth muscle tumors, but most cases are diagnosed purely on histologic grounds.

Perivascular epithelioid cell tumor of the uterus and pelvic cavity

Background

Primary perivascular epithelioid cell tumors (PEComas) of the female reproductive tract have been primarily reported as case reports owing to their clinical rarity. Limited incidence rates and clinical case data hinder a comprehensive understanding of the risks and invasiveness of this disease. We discuss herein the diagnosis, treatment, and prognosis of this disease to enhance comprehension and therapeutic strategies.

Methods

We conducted a clinical analysis of patients with PEComa treated at the Gynecology Department of The West China Second University Hospital of Sichuan University between May 2018 and January 2024. Diagnosis and treatment were evaluated based on pertinent literature.

Results

Overall, eight patients (seven patients with tumors in the uterus and one patient with tumors in the pelvic cavity) were evaluated. One patient with PEComa of unknown malignant potential and two patients with malignant PEComa underwent hysterectomy and bilateral adnexectomy with or without adjuvant therapy and did not develop recurrence. Meanwhile, three patients who underwent lesion resection only exhibited radiological evidence of new lesions. Furthermore, postoperative imaging identified new pulmonary nodules in three patients.

Conclusion

Although the current criteria are generally effective in assessing the tumor invasiveness of PEComa, emphasizing the significance of complete lesion resection remains crucial. Inadequate treatment significantly increases the risks of recurrence and metastasis. Additionally, the prevalence of pulmonary metastases may have been underestimated. Refining risk stratification to prevent overtreatment of low-grade malignancies or overlooking highly aggressive tumors is an important area for further study.

Gynecologic perivascular epithelioid cell tumors (PEComas): a review of recent evidence

Gynecologic perivascular epithelioid cell (PEC) tumors, or 'PEComas,' represent a rare and intriguing subset of tumors within the female reproductive tract. This systematic literature review aims to provide an updated understanding of gynecologic PEComas based on available literature and data. Although PEComa is rare, there are varied tumor-site presentations across gynecologic organs, with uterine PEComas being the most prevalent. There is scarce high-quality literature regarding gynecologic PEComa, and studies on malignant PEComa underscore the challenges in diagnosis. Among the diverse mutations, mTOR alterations are the most prominent. Survival analysis reveals a high rate of local recurrence and metastatic disease, which commonly affects the lungs. Treatment strategies are limited, however mTOR inhibitors have pivotal role when indicated and chemotherapy may also be used. with some cases demonstrating promising responses. The paucity of data underscores the need for multicentric studies, an international registry for PEComas, and standardized reporting in case series to enhance clinical and pathological data.

Uterine Leiomyosarcoma Associated With Perivascular Epithelioid Cell Tumor: A Phenomenon of Differentiation/Dedifferentiation and Evidence Suggesting Cell-of-Origin

Perivascular epithelioid cell tumor (PEComa) is a mesenchymal tumor thought to originate from perivascular epithelioid cells (PECs). The normal counterpart to PEC, however, has not been identified in any human organ, and the debate as to whether PEComa is related to smooth muscle tumors has persisted for many years. The current series characterizes 4 cases of uterine leiomyosarcoma (LMS) coexisting with PEComas. All cases exhibited an abrupt transition from the LMS to PEComa components. The LMS component displayed typical spindled morphology and fascicular growth pattern and was diffusely positive for desmin and smooth muscle myosin heavy chain, completely negative for HMB-45 and Melan A, and either negative or had focal/weak expression of cathepsin K and GPNMB. In contrast, the PEComa tumor cells in case 1 contained glycogen or lipid-distended cytoplasm with a foamy appearance (low grade), and in cases 2, 3, and 4, they displayed a similar morphology characterized by epithelioid cells with eosinophilic and granular cytoplasm and high-grade nuclear atypia. Different from the LMS component, the epithelioid PEComa cells in all cases were focally positive for HMB-45, and diffusely immunoreactive for cathepsin K and GPNMB. Melan A was focally positive in cases 1 and 3. Loss of fumarate hydratase expression (case 1) and RB1 expression (cases 2, 3, 4) was identified in both LMS and PEComa components, indicating that they are clonally related. In addition, both components showed an identical TP53 p.R196* somatic mutation and complete loss of p53 and ATRX expression in case 2 and complete loss of p53 expression in case 3. We hypothesize that LMSs containing smooth muscle progenitor cells may give rise to divergent, lineage-specific PEComatous lesions through differentiation or dedifferentiation. While we do not dispute the recognition of PEComas as a distinct entity, we advocate the hypothesis that modified smooth muscle cells represent the origin of a subset of PEComas, and our case series provides evidence to suggest this theory.

Primary omental smooth muscle tumor in an adult male: a diagnostic dilemma for leiomyoma: a case report

BACKGROUND

The greater omentum comprises peritoneal, adipose, vascular, and lymphoid tissues. Most omental malignancies are metastatic tumors, and the incidence of primary tumors is rare. We report on a prior omental smooth muscle tumor case in an adult male patient.

CASE PRESENTATION

A 54-year-old Japanese male patient with no relevant medical history was diagnosed with an abdominal mass during a routine medical checkup. Subsequent contrast-enhanced computed tomography revealed a mass of approximately 3 cm in size in the greater omentum, and a laparotomy was performed. A 27 × 25 × 20 mm raised lesion was found in the omentum. Microscopically, spindle cells were observed and arranged in whorls and fascicles. Individual tumor cells had short spindle-shaped nuclei with slightly increased chromatin and were characterized by a slightly eosinophilic, spindle-shaped cytoplasm. The mitotic count was less than 1 per 50 high-power fields. The tumor cells showed positive immunoreactivity for α smooth muscle actin, HHF35, and desmin on immunohistochemical examination. The Ki-67 labeling index using the average method was 1.76% (261/14806). No immunoreactivity was observed for any of the other tested markers. We considered leiomyoma owing to a lack of malignant findings. However, primary omental leiomyoma has rarely been reported, and it can be difficult to completely rule out the malignant potential of smooth muscle tumors in soft tissues. Our patient was decisively diagnosed with a primary omental smooth muscle tumor considering leiomyoma. Consequently, the patient did not undergo additional adjuvant therapy and was followed up. The patient was satisfied with treatment and showed neither recurrence nor metastasis at the 13-month postoperative follow-up.

DISCUSSION AND CONCLUSION

We encountered a primary smooth muscle tumor of the greater omentum with no histological findings suggestive of malignancy in an adult male patient. However, omental smooth muscle tumors are extremely difficult to define as benign, requiring careful diagnosis. Further case reports with long-term follow-up and case series are required to determine whether a true omental benign smooth muscle tumor (leiomyoma) exists. In addition, proper interpretation of the Ki-67 labeling index should be established. This case study is a foundation for future research.

A Case Report of Malignant Perivascular Epithelioid Cell Tumors of the Uterus and Literature Review

Perivascular epithelioid cell tumors (PEComas) are rare mesenchymal tumors originating from perivascular epithelioid cells. In gynecological system, the uterus is one of the most common sites affected by PEComas. Most PEComas are benign, and patients usually have a good prognosis. However, malignant uterus PEComa is rare, and better comprehensive epidemiological investigations are needed. To date, there are a few reported cases of uterus PEComa. We herein report a rare case of malignant PEComa occurred in the uterine corpus and cervix, possibly accompanied by pulmonary lymphangioleiomyomatosis (PLAM). In addition, 55 cases of malignant uterus PEComa were picked out and collected in the data base of PubMed and Medline. On the one hand, the age of onset, population distribution, clinical manifestations, metastatic sites and routes of metastasis were analysed. On the other hand, a summary of the epidemiology, pathogenesis, diagnosis, and treatments of uterus PEComa was given.

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.

Systematic analysis of perivascular epithelioid cell neoplasms in the female reproductive tract: a comprehensive review

Perivascular epithelioid cell neoplasms (PEComas) are rare mesenchymal lesions, with gynecological PEComas accounting for just over a quarter of cases. Limited reports exist on gynecological PEComa, primarily treated with surgery; adjuvant therapy is considered in high-risk cases. This systematic review aims to summarize the origin and clinical, pathological and molecular characteristics of uterine PEComa, focusing on treatment options for gynecological PEComa. A comprehensive PubMed review of gynecological PEComa reports was conducted. A detailed examination of the literature ensured a thorough understanding. Gynecological PEComa diagnosis relies on histology and immunology. Despite therapy controversies, surgery remains the mainstay. Adjuvant therapy efficacy in high-risk cases is uncertain. mTOR inhibitors are the first line; alternative treatments, including angiogenesis and aromatase inhibitors, should be considered.

Uterine collision tumor (PEComa and endometrioid carcinoma) in a tuberous sclerosis patient: a case report

Perivascular epithelioid cell tumors are very rare mesenchymal neoplasms arising in various locations, such as the female genital tract, kidney, lung, prostate, bladder, pancreas, soft tissues, and bone. They possess a unique immunophenotype, co-expressing myogenic and melanocytic markers; molecular findings include mutations of tuberous sclerosis complex and translocations of transcription factor E3, a member of the microphthalmia transcription factor gene family. We herewith report a uterine collision tumor consisting of a perivascular epithelioid cell tumor and a moderately differentiated endometrial endometrioid carcinoma in a patient with genetically proven tuberous sclerosis; two leiomyomas were also found in contact with the tumor. Although two such cases one with a benign and another with a malignant perivascular epithelioid cell tumor have previously been reported, ours is, to our knowledge, the first reported in a tuberous sclerosis patient.

A Clinicopathologic and Molecular Characterization of Uterine Sarcomas Classified as Malignant PEComa

Perivascular epithelioid cell tumors (PEComas) are a distinctive group of mesenchymal neoplasms that demonstrate features of smooth muscle and melanocytic differentiation. Here, we present the clinicopathologic, immunohistochemical, and molecular features of 15 uterine sarcomas diagnosed as malignant PEComa. The median patient age was 56 years (range: 27 to 86 y). The median tumor size was 8.0 cm (range: 5.0 to 14.0 cm). All tumors were classified as malignant based on the presence of mitoses (15/15; 100%), necrosis (15/15; 100%), lymphovascular invasion (8/15; 53%), and high nuclear grade (13/15; 87%). Molecular analysis revealed the mammalian target of rapamycin pathway gene mutations in 7 cases (47%), including mutually exclusive variants in TSC1 (27%) and TSC2 (20%). Recurrent alterations were also identified in TP53 (53%), RB1 (30%), ATRX (33%), and BRCA2 (13%). Tumors with inactivating ATRX mutations all demonstrated loss of ATRX expression by immunohistochemistry. Loss of expression was also observed in 2 tumors without demonstrable ATRX alterations. Clinical follow-up was available for 14 patients (range: 5 to 92 mo; median: 15 mo). Five patients developed local recurrence and 9 developed metastases; 2 patients died of their disease. Our series expands the spectrum of molecular events in tumors diagnosed as malignant PEComa and further highlights the important role of targeted sequencing in tumors with focal melanocytic marker expression.

Update on Uterine Mesenchymal Neoplasms

This review focuses on recent advances in epithelioid and myxoid uterine mesenchymal neoplasms, a category of tumors whereby diagnostic criteria have been rapidly evolving due to advances in molecular testing. Pertinent clinicopathological and molecular features are highlighted for perivascular epithelioid cell tumors, uterine tumors resembling ovarian sex cord tumors, BCOR/BCORL1-altered high-grade endometrial stromal sarcomas, and inflammatory myofibroblastic tumors. Novel developments in epithelioid and myxoid leiomyosarcomas are briefly discussed, and differential diagnoses with key diagnostic criteria are provided for morphologic mimickers.

Uterine PEComas: correlation between melanocytic marker expression and TSC alterations/TFE3 fusions

Uterine PEComas often present a diagnostic challenge as they share morphological and immunohistochemical features with smooth muscle tumors. Herein we evaluated a series of 19 uterine PEComas to compare the degree of melanocytic marker expression with their molecular profile. Patients ranged from 32-77 (median 48) years, with six tumors classified as malignant based on the modified gynecologic-specific prognostic algorithm. All patients with malignant PEComas were alive with disease or dead  of disease at last follow-up, while all those of uncertain malignant potential were alive and well (median follow-up, 47 months).Seventeen of 19 (89%) PEComas harbored either a TSC1 or TSC2 alteration. One of the two remaining tumors showed a TFE3 rearrangement, but the other lacked alterations in all genes evaluated. All showed at least focal (usually strong) positivity for HMB-45, with 15/19 (79%) having >50% expression, while the tumor lacking TSC or TFE3 alterations was strongly positive in 10% of cells. Melan-A and MiTF were each positive in 15/19 (79%) tumors, but staining extent and intensity were much more variable than HMB-45. Five of six (83%) malignant PEComas also harbored alterations in TP53, ATRX, or RB1, findings not identified in any tumors of uncertain malignant potential. One malignant PEComa was microsatellite-unstable/mismatch repair protein-deficient.In summary, TSC alterations/TFE3 fusions and diffuse (>50%) HMB-45 expression are characteristic of uterine PEComas. In morphologically ambiguous mesenchymal neoplasms with myomelanocytic differentiation, especially those with metastatic or recurrent disease, next-generation sequencing is recommended to evaluate for TSC alterations; as such, patients can be eligible for targeted therapy.

Genomic Profiling Aids Classification of Diagnostically Challenging Uterine Mesenchymal Tumors With Myomelanocytic Differentiation

Although diagnosis of high-grade uterine mesenchymal tumors (UMTs) exhibiting classic morphologic features is straightforward, diagnosis is more challenging in tumors in which prototypical features are poorly developed, focal, and/or coexist with features seen in other neoplasms. Here, we sought to define the repertoire of somatic genetic alterations in diagnostically challenging UMTs with myomelanocytic differentiation, including some reported as perivascular epithelioid cell tumors (PEComas). In 17 samples from 15 women, the tumors were histologically heterogenous. Immunohistochemical expression of at least 1 melanocytic marker (HMB45, Melan-A, or MiTF) was identified in all tumors, and of myogenic markers (desmin or smooth muscle actin) in most tumors. Targeted massively parallel sequencing revealed several genetic alterations, most commonly in TP53 (41% mutation, 12% deletion), TSC2 (29% mutation, 6% deletion), RB1 (18% deletion), ATRX (24% mutation), MED12 (12% mutation), BRCA2 (12% deletion), CDKN2A (6% deletion) as well as FGFR3, NTRK1, and ERBB3 amplification (each 6%). Gene rearrangements (JAZF1-SUZ12; DNAJB6-PLAG1; and SFPQ-TFE3) were identified in 3 tumors. Integrating histopathologic, immunohistochemical, and genetic findings, tumors from 4 patients were consistent with malignant PEComa (1 TFE3-rearranged); 6 were classified as leiomyosarcomas; 3 showed overlapping features of PEComa and other sarcoma types (leiomyosarcoma or low-grade endometrial stromal sarcoma); and 2 were classified as sarcoma, not otherwise specified. Our findings suggest that diagnostically challenging UMTs with myomelanocytic differentiation represent a heterogenous group of neoplasms which harbor a diverse repertoire of somatic genetic alterations; these genetic alterations can aid classification.

Uterine plexiform tumourlets: multifocal and solitary cases with subsets expressing melanocytic markers

AIMS

Uterine plexiform tumourlets are traditionally regarded as microscopic epithelioid leiomyomas. They are typically solitary incidental findings, but may be multifocal (plexiform leiomyomatosis). We aim to report novel immunohistochemical and morphological findings, specifically the presence of spindled and epithelioid cell nodules, in these lesions.

METHODS AND RESULTS

Three cases of plexiform leiomyomatosis and 16 solitary plexiform tumourlets were included. Two cases of plexiform leiomyomatosis and four solitary plexiform tumourlets demonstrated spindled and epithelioid cell nodules which, in one of the former cases, formed expansile masses up to 15 mm. The nodules demonstrated mild cytological atypia and occasional mitotic activity, and they were associated with a myxoid stroma and a lymphohistiocytic infiltrate which imparted a granulomatous appearance to the microscopic lesions. The plexiform tumourlets (solitary and multifocal) consistently expressed desmin, smooth muscle actin, ER and PR, and they commonly co-expressed melanocytic and perivascular epithelioid cell (PEC) markers HMB45, MiTF and cathepsin K. The spindled and epithelioid cell nodules were generally negative for myoid markers and hormone receptors, but expressed p16, cyclin D1 and TFE3. All lesions tested were negative for cytokeratin, S100, melanA, inhibin, EMA, ALK and BCOR; fluorescence in-situ hybridisation was negative for ALK, TFE3 and BCOR rearrangements in one of the larger spindled and epithelioid cell nodules.

CONCLUSIONS

Plexiform tumourlets commonly co-express myoid and melanocytic markers and may represent part of the spectrum of gynaecological PEC-related lesions. Some cases are associated with spindled and epithelioid cell nodules that could potentially mimic other uterine myxoid neoplasms.

Perivascular epithelioid cell tumors (PEComa) of the gynecologic tract

PEComas of the female genital tract are rare mesenchymal neoplasms that are most common in the uterus, but also may occur in other gynecologic locations. As they morphologically and immunohistochemically resemble smooth muscle tumors, distinction between the two entities is often challenging, and may be aided by molecular analysis. Thus far, two distinct molecular groups-classic PEComas with TSC mutations and TFE3-translocation associated PEComas with TFE3 fusions have been described. Recognition of the first group is imperative as these patients may benefit from targeted therapy with mTOR inhibitors, if malignant. This review will focus on recognition of the morphologic and immunophenotypic features of PEComas, as well as the role of molecular testing in their diagnosis and treatment, analysis of the different algorithms to predict behavior, and differential diagnosis.