MED12 and uterine smooth muscle oncogenesis: State of the art and perspectives

Pathogenesis of uterine fibroids: current understanding and future directions

Fibroids are benign uterine tumors characterized by the proliferation of uterine smooth muscle cells, embedded in an abundant extracellular matrix. Their prevalence is estimated to be >50% in women aged >45 years. Fibroids represent a considerable health burden. It is time to acquire a deeper mechanistic understanding of uterine fibroid-related etiology and pathogenesis, which may help pinpoint new strategies and an individualized approach. There is a need to gather prospective data and conduct studies to compare alternative approaches and assess long-term outcomes with respect to quality of life, recurrence of symptoms (bleeding and bulk symptoms), fertility, and even complications The goal of this review was to evaluate the widely accepted pathogenesis and identify risks factors and future directions for clinical and basic research into fibroids.

Pan-cancer Genomic Analysis of AXL Mutations Reveals a Novel, Recurrent, Functionally Activating AXL W451C Alteration Specific to Myxofibrosarcoma

Myxofibrosarcoma (MFS) is a common soft tissue sarcoma of the elderly that typically shows low tumor mutational burden, with mutations in TP53 and in genes associated with cell cycle checkpoints ( RB1 , CDKN2A ). Unfortunately, no alterations or markers specific to MFS have been identified and, as a consequence, there are no effective targeted therapies. The receptor tyrosine kinase AXL, which drives cellular proliferation, is targetable by new antibody-based therapeutics. Expression of AXL messenger RNA is elevated in a variety of sarcoma types, with the highest levels reported in MFS, but the pathogenic significance of this finding remains unknown. To assess a role for AXL abnormalities in MFS, we undertook a search for AXL genomic alterations in a comprehensive genomic profiling database of 463,546 unique tumors (including 19,879 sarcomas, of which 315 were MFS) interrogated by targeted next-generation DNA and/or RNA sequencing. Notably, the only genomic alterations recurrent in a specific sarcoma subtype were AXL W451C (n = 8) and AXL W450C (n = 2) mutations. The tumors involved predominantly older adults (age: 44 to 81 [median: 72] y) and histologically showed epithelioid and spindle-shaped cells in a variably myxoid stroma, with 6 cases diagnosed as MFS, 3 as undifferentiated pleomorphic sarcoma (UPS), and 1 as low-grade sarcoma. The AXL W451C mutation was not identified in any non-sarcoma malignancy. A review of publicly available data sets revealed a single AXL W451C-mutant case of UPS that clustered with MFS/UPS by methylation profiling. Functional studies revealed a novel activation mechanism: the W451C mutation causes abnormal unregulated dimerization of the AXL receptor tyrosine kinase through disulfide bond formation between pairs of mutant proteins expressing ectopic cysteine residues. This dimerization triggers AXL autophosphorylation and activation of downstream ERK signaling. We further report sarcomas of diverse histologic subtypes with AXL gene amplifications, with the highest frequency of amplification identified in MFS cases without the W451C mutation. In summary, the activating AXL W451C mutation appears highly specific to MFS, with a novel mechanism to drive unregulated signaling. Moreover, AXL gene amplifications and messenger RNA overexpression are far more frequent in MFS than in other sarcoma subtypes. We conclude that these aberrations in AXL are distinct features of MFS and may aid diagnosis, as well as the selection of available targeted therapies.

The Mediator Complex Subunit 12 (MED-12) Gene and Uterine Fibroids: a Systematic Review

Uterine leiomyomas are the most common tumor of reproductive-age women worldwide. Although benign, uterine fibroids cause significant morbidity and adversely impact the quality of life for affected women. Somatic mutations in the exon 2 of the mediator complex subunit 12 (MED-12) gene represent the most common single gene mutation associated with uterine leiomyomas. The objective of this review was to evaluate the current role of MED-12 mutation in the pathophysiology of uterine fibroids, to assess the prevalence of MED-12 mutation among different populations, and to identify the most common subtypes of MED-12 mutations found in uterine fibroids. A comprehensive search was conducted using Pubmed, Embase, Scopus, and the Web of Science. English-language publications that evaluated MED-12 mutation and uterine fibroids in humans, whether experimental or clinical, were considered. We identified 380 studies, of which 23 were included, comprising 1353 patients and 1872 fibroid tumors. Of the total number of tumors analyzed, 1045 (55.8%) harbored a MED-12 mutation. Among the 23 studies included, the frequency of MED-12 mutation varied from 31.1 to 80% in fibroid samples. The most common type of MED-12 mutation was a heterozygous missense mutation affecting codon 44 of exon 2, specifically the nucleotide 131. Studies reported that MED-12 mutation acts by increasing levels of AKT and disrupting the cyclin C-CDK8/19 kinase activity. The overall average prevalence of MED-12 mutation in uterine fibroids was found to be 55.8% across the global population, though the frequency varied greatly among different countries.

Benign Metastasizing Leiomyoma: Is "Wait and Watch" Strategy Feasible?

Benign metastasizing leiomyoma (BML) is a rare disease that affects women with a history of uterine leiomyoma. The aim of this study is to investigate the clinical characteristics and outcome patterns. We collected 385 cases from previous reports indexed in PubMed and Google Scholar and made a thorough review. All relevant clinical parameters were carefully reviewed, including age at diagnosis, clinical presentations, course of disease, medical history, imaging, molecular tests, treatment, and outcomes. Univariate survival analysis was performed to investigate the effects of treatment strategies on outcomes. The mean age at diagnosis was 46.2 years. The most common site for the metastasis was lung, and followed by abdomen/pelvis/retroperitoneum, bone, lymph nodes, and heart. The medical histories and molecular alterations were non-specific, and the pathogenesis was still unclear. Due to its unresectable nature, hormone deprivation treatment, including oophorectomy and hormone drugs, is the most effective strategy to reduce or delay tumor progression. The present study may provide a useful consultation for diagnosing and managing BMLs.

PLP1 may serve as a potential diagnostic biomarker of uterine fibroids

Objective: We aim to identify the crucial genes or potential biomarkers associated with uterine fibroids (UFs), which may provide clinicians with evidence about the diagnostic biomarker of UFs and reveal the mechanism of its progression.

Methods: The gene expression and genome-wide DNA methylation profiles were obtained from Gene Expression Omnibus database (GEO). GSE45189, GSE31699, and GSE593 datasets were included. GEO2R and Venn diagrams were used to analyze the differentially expressed genes (DEGs) and extract the hub genes. Gene Ontology (GO) analysis was performed by the online tool Database for Annotation, Visualization, and Integrated Discovery (DAVID). The mRNA and protein expression of hub genes were validated by RT-qPCR, western blot, and immunohistochemistry. The receiver operating characteristic (ROC) curve was used to evaluate the diagnostic value.

Results: We detected 22 DEGs between UFs and normal myometrium, which were enriched in cell maturation, apoptotic process, hypoxia, protein binding, and cytoplasm for cell composition. By finding the intersection of the data between differentially expressed mRNA and DNA methylation profiles, 3 hub genes were identified, including transmembrane 4 L six family member 1 (TM4SF1), TNF superfamily member 10 (TNFSF10), and proteolipid protein 1 (PLP1). PLP1 was validated to be up-regulated significantly in UFs both at mRNA and protein levels. The area under the ROC curve (AUC) of PLP1 was 0.956, with a sensitivity of 79.2% and a specificity of 100%. Conclusion: Overall, our results indicate that PLP1 may be a potential diagnostic biomarker for uterine fibroids.

Comprehensive Review of Uterine Fibroids: Developmental Origin, Pathogenesis, and Treatment

Uterine fibroids are benign monoclonal neoplasms of the myometrium, representing the most common tumors in women worldwide. To date, no long-term or noninvasive treatment option exists for hormone-dependent uterine fibroids, due to the limited knowledge about the molecular mechanisms underlying the initiation and development of uterine fibroids. This paper comprehensively summarizes the recent research advances on uterine fibroids, focusing on risk factors, development origin, pathogenetic mechanisms, and treatment options. Additionally, we describe the current treatment interventions for uterine fibroids. Finally, future perspectives on uterine fibroids studies are summarized. Deeper mechanistic insights into tumor etiology and the complexity of uterine fibroids can contribute to the progress of newer targeted therapies.

Differential Expression of Super-Enhancer-Associated Long Non-coding RNAs in Uterine Leiomyomas

Super-enhancer-associated long non-coding RNAs (SE-lncRNAs) are a specific set of lncRNAs transcribed from super-enhancer (SE) genomic regions. Recent studies have revealed that SE-lncRNAs play essential roles in tumorigenesis through the regulation of oncogenes. The objective of this study was to elucidate the expression profile of SE-lncRNAs with concurrent assessment of associated mRNAs in leiomyomas and paired myometrium. Arraystar SE-lncRNAs arrays were used to systematically profile the differentially expressed SE-lncRNAs along with the corresponding SE-regulated protein coding genes in eight leiomyomas and paired myometrium. The analysis indicated 7680 SE-lncRNAs were expressed, of which 721 SE-lncRNAs were overexpressed, while 247 SE-lncRNAs were underexpressed by 1.5-fold or greater in leiomyoma. Thirteen novel SE-lncRNAs and their corresponding protein coding genes were selected, and their expression was confirmed in eighty-one paired leiomyoma tissues by quantitative real-time PCR. The thirteen pairs of SE-lncRNAs and their corresponding protein coding genes included RP11-353N14.2/CBX4, SOCS2-AS1/SOCS2, RP1-170O19.14/HOXA11, CASC15/PRL, EGFLAM-AS1/EGFLAM, RP11-225H22/NEURL1, RP5-1086K13.1/CD58, AC092839.3/SPTBN1, RP11-69I8.3/CTGF, TM4SF1-AS1/TM4SF1, RP11-373D23/FOSL2, RP11-399K21.11/COMTD1, and CTB-113P19.1/SPARC. Among these SE-lncRNAs, the expression of SOCS2-AS1/SOCS2, RP11-353N14.2/CBX4, RP1-170O19.14/HOXA11, and RP11-225H22/NEURL1 was significantly higher in African Americans as compared with Caucasians. The expression of RP11-353N14.2/CBX4, SOCS2-AS1/SOCS2, CASC15/PRL, and CTB-113P19.1/SPARC was significantly higher in tumors with MED12-mutation-positive as compared with MED12-mutation-negative tumors. Collectively, our results indicate that the differential expression of SE in leiomyomas is another mechanism contributing to dysregulation of protein coding genes in leiomyomas and that race and MED12 mutation can influence the expression of a select group of SE.

High-Grade Spindle Cell Lesions of the Breast: Key Pathologic and Clinical Updates

Most of the high-grade spindle cell lesions of the breast are malignant phyllodes tumors (MPTs), spindle cell carcinomas (SpCCs), and matrix-producing metaplastic breast carcinomas (MP-MBCs). MPTs have neoplastic spindle stromal cells and a classic leaf-like architecture with subepithelial stromal condensation. MPTs are often positive for CD34, CD117, and bcl-2 and are associated with MED12, TERT, and RARA mutations. SpCCs and MP-MBCs are high-grade metaplastic carcinomas, whereas neoplastic epithelial cells become spindled or show heterologous mesenchymal differentiation, respectively. The expression of epithelial markers must be evaluated to make a diagnosis. SAS, or rare metastatic spindle cell tumors, are seen in the breast, and clinical history is the best supporting evidence. Surgical resection is the standard of care.

The role of mediator subunit 12 in tumorigenesis and cancer therapeutics (Review)

Mediator complex subunit 12 (MED12) is a subunit of Mediator, a large multi-subunit protein complex that acts an important regulator of transcription. Specifically, MED12 is an integral part of the kinase module of Mediator along with MED13, CyclinC (CycC) and CDK8. Structural studies have indicated that MED12 makes a direct connection to CycC through a specific interface and thereby functions to create a link between MED13 and CycC-CDK8. Disruption of the MED12-CycC interface often leads to dysregulated CDK8 kinase activity, which has important physiological implications. For example, a number of studies have indicated that mutations within MED12 can lead to the formation of benign or malignant tumors, either as a result of MED12-CycC disruption or through distinct independent mechanisms. Furthermore, recent studies have indicated that the N-terminal portion of MED12 forms a direct connection to CDK8. Mutations within MED12 do not appear to disrupt the physical connection to CDK8, but rather abrogate CDK8 kinase activity. Thus, mutations in MED12 can cause disruption of CDK8 kinase activity through two separate mechanisms. The aim of the present review article was to discuss the MED12 mutational landscape in a variety of benign and malignant tumors, as well as the mechanistic basis behind tumorigenesis. Furthermore, the link between MED12 and drug resistance has also been discussed, as well as potential cancer therapeutics related to MED12-altered tumors.

Multiple Mutations in Exon-2 of Med-12 Identified in Uterine Leiomyomata

Background:

Uterine leiomyomata (UL), commonly known as uterine fibroids, are benign smooth muscle tumors of the myometrium. They cause pelvic pain, abnormal uterine bleeding, and infertility in women of reproductive age. The ovarian hormone estrogen is the main stimulator for the fibroid growth. The etiology is not yet clearly understood; however, UL are believed to be monoclonal tumors arising from a common progenitor cell. Chromosomal cytogenetic abnormalities have been demonstrated in 40–50% of the fibroids. The most frequent tumor specific genetic alterations in UL were identified in exon-2 of Mediator Complex Subunit 12 (MED-12).

Methods:

In the present study, twenty-two multiple fibroids were evaluated both from the same uterus and from different uteri, of four women, for somatic mutations in hotspot region of MED-12. The tissue DNA of the UL’s was isolated, amplified by PCR visualized on gel and sent for Sanger sequencing.

Results:

The results indicate several variants in exon-2 and flanking intronic regions, seven exonic variants and five intronic variants which provide evidence that multiple UL in the same uterus may not be clonal in origin.

Conclusion:

This study indicates genetic heterogeneity. UL may not have a clonal origin, these exon-2 variants of MED-12 gene could be involved in UL progression.

An Intraluminal Parasitic Leiomyoma of the Sigmoid Colon and Potential Pathogenetic Mechanisms

Uterine leiomyomas are the most common benign tumor of the female pelvis. Parasitic leiomyomas are an extremely rare entity of leiomyoma occurrence found at extrauterine sites. They are mostly diagnosed in patients with a history of gynecologic procedures and morcellators use during laparoscopic leiomyoma resection. Here we present an extraordinary case of an intraluminal leiomyoma of the sigmoid colon that was incidentally discovered during total abdominal hysterectomy and bilateral salpingo-oophorectomy, performed due to leiomyomatous uterus in a female patient with no history of previous gynecologic operations. Potential pathogenetic mechanisms that can explain the co-occurrence of leiomyomas in the uterus and the sigmoid colon are also reviewed and include genetic predisposition, the stem cell theory of leiomyomas formation, and lymphatic and vascular spread.

Identification and characterization of the mediator kinase-dependent myometrial stem cell phosphoproteome

OBJECTIVE

To identify, in myometrial stem/progenitor cells, the presumptive cell of origin for uterine fibroids, substrates of Mediator-associated cyclin dependent kinase 8/19 (CDK8/19), which is known to be disrupted by uterine fibroid driver mutations in Mediator complex subunit 12 (MED12).

DESIGN

Experimental study.

SETTING

Academic research laboratory.

PATIENT(S)

Women undergoing hysterectomy for uterine fibroids.

INTERVENTION(S)

Stable isotopic labeling of amino acids in cell culture (SILAC) coupled with chemical inhibition of CDK8/19 and downstream quantitative phosphoproteomics and transcriptomic analyses in myometrial stem/progenitor cells.

MAIN OUTCOME MEASURE(S)

High-confidence Mediator kinase substrates identified by SILAC-based quantitative phosphoproteomics were determined using an empirical Bayes analysis and validated orthogonally by in vitro kinase assay featuring reconstituted Mediator kinase modules comprising wild-type or G44D mutant MED12 corresponding to the most frequent uterine fibroid driver mutation in MED12. Mediator kinase-regulated transcripts identified by RNA sequencing were linked to Mediator kinase substrates by computational analyses.

RESULT(S)

A total of 296 unique phosphosites in 166 proteins were significantly decreased (≥ twofold) upon CDK8/19 inhibition, including 118 phosphosites in 71 nuclear proteins representing high-confidence Mediator kinase substrates linked to RNA polymerase II transcription, RNA processing and transport, chromatin modification, cytoskeletal architecture, and DNA replication and repair. Orthogonal validation confirmed a subset of these proteins, including Cut Like Homeobox 1 (CUX1) and Forkhead Box K1 (FOXK1), to be direct targets of MED12-dependent CDK8 phosphorylation in a manner abrogated by the most common uterine fibroid driver mutation (G44D) in MED12, implicating these substrates in disease pathogenesis. Transcriptome-wide profiling of Mediator kinase-inhibited myometrial stem/progenitor cells revealed alterations in cell cycle and myogenic gene expression programs to which Mediator kinase substrates could be linked directly. Among these, CUX1 is an established transcriptional regulator of the cell cycle whose corresponding gene on chromosome 7q is the locus for a recurrent breakpoint in uterine fibroids, linking MED12 and Mediator kinase with CUX1 for the first time in uterine fibroid pathogenesis. FOXK1, a transcriptional regulator of myogenic stem cell fate, was found to be coordinately enriched along with kinase, but not core, Mediator subunits in myometrial stem/progenitor cells compared with differentiated uterine smooth muscle cells.

CONCLUSION(S)

These studies identify a new catalog of pathologically and biologically relevant Mediator kinase substrates implicated in the pathogenesis of MED12 mutation-positive uterine fibroids, and further uncover a biochemical basis to link Mediator kinase activity with CUX1 and FOXK1 in the regulation of myometrial stem/progenitor cell fate.

Long Noncoding RNA MIAT Modulates the Extracellular Matrix Deposition in Leiomyomas by Sponging MiR-29 Family

The objective of this study was to determine the expression and functional role of a long noncoding RNA (lncRNA) MIAT (myocardial infarction-associated transcript) in leiomyoma pathogenesis. Leiomyoma compared with myometrium (n = 66) expressed significantly more MIAT that was independent of race/ethnicity and menstrual cycle phase but dependent on MED12 (mediator complex subunit 12) mutation status. Leiomyomas bearing the MED12 mutation expressed higher levels of MIAT and lower levels of microRNA 29 family (miR-29a, -b, and -c) compared with MED12 wild-type leiomyomas. Using luciferase reporter activity and RNA immunoprecipitation analysis, MIAT was shown to sponge the miR-29 family. In a 3-dimensional spheroid culture system, transient transfection of MIAT siRNA in leiomyoma smooth muscle cell (LSMC) spheroids resulted in upregulation of miR-29 family and downregulation of miR-29 targets, collagen type I (COL1A1), collagen type III (COL3A1), and TGF-β3 (transforming growth factor β-3). Treatment of LSMC spheroids with TGF-β3 induced COL1A1, COL3A1, and MIAT levels, but repressed miR-29 family expression. Knockdown of MIAT in LSMC spheroids blocked the effects of TGF-β3 on the induction of COL1A1 and COL3A1 expression. Collectively, these results underscore the physiological significance of MIAT in extracellular matrix accumulation in leiomyoma.

Systematic molecular and clinical analysis of uterine leiomyomas from fertile-aged women undergoing myomectomy

STUDY QUESTION

What are the distributions and associated clinical characteristics of mediator complex subunit 12 (MED12), high mobility group AT-hook 2 (HMGA2) and fumarate hydratase (FH) aberrations in uterine leiomyomas from fertile-aged myomectomy patients?

SUMMARY ANSWER

These driver mutations account for the majority (83%) of tumours in fertile-aged patients.

WHAT IS KNOWN ALREADY

Alterations affecting MED12, HMGA2 and FH account for 80-90% of uterine leiomyomas from middle-aged hysterectomy patients, while the molecular background of tumours from young myomectomy patients has not been systematically studied.

STUDY DESIGN, SIZE, DURATION

A retrospective series of 361 archival uterine leiomyoma samples from 234 women aged ≤45 years undergoing myomectomy in 2009-2014 was examined. Associations between the molecular data and detailed clinical information of the patients and tumours were analysed.

PARTICIPANTS/MATERIALS, SETTING, METHODS

DNA was extracted from formalin-fixed paraffin-embedded samples and MED12 exons 1 and 2 were sequenced to identify mutations. Level of HMGA2 expression was evaluated by immunohistochemistry. Biallelic FH inactivation was analysed with 2-succinylcysteine staining, which is an indirect method of assessing FH deficiency. All patients' medical histories were reviewed, and clinical information of patients and tumours was combined with molecular data.

MAIN RESULTS AND THE ROLE OF CHANCE

The median age at operation was 34 years. The majority (58%) of patients were operated on for a single leiomyoma. Known driver mutations were identified in 83% of tumours (71% MED12; 9% HMGA2; 3% FH). In solitary leiomyomas, the MED12 mutation frequency was only 43%, and 29% were wild-type for all driver alterations. MED12 mutations were associated with multiple tumours, smaller tumour size and subserosal location.

LIMITATIONS, REASONS FOR CAUTION

Although comprehensive, the study is retrospective in nature and all samples have been collected for routine diagnostic purposes. The use of paraffin-embedded samples and immunohistochemistry may have led to an underestimation of mutations. Due to the limited sample size and rarity of especially FH-deficient leiomyomas, the data are partly descriptive.

WIDER IMPLICATIONS OF THE FINDINGS

The contribution of driver mutations in leiomyomas from young myomectomy patients is comparable to tumours obtained from hysterectomies of mostly middle-aged women. Our results support the earlier findings that MED12 mutations are associated with multiple tumours, smaller tumour size and subserosal location. The study emphasizes the distinct molecular background of solitary leiomyomas, and more research is needed to clarify the underlying causes of the notable proportion of wild-type leiomyomas.

STUDY FUNDING/COMPETING INTEREST(S)

The study was supported by the Academy of Finland (307773), the Sigrid Jusélius Foundation, the Cancer Foundation Finland and the iCAN Digital Precision Cancer Medicine Flagship. The authors declare no conflicts of interest.

TRIAL REGISTRATION NUMBER

N/A.

Emerging Roles of Long Non-coding RNAs in Uterine Leiomyoma Pathogenesis: a Review

Uterine leiomyoma (UL), as the most prevalent type of women's health disorders, is a benign tumor that originates from the smooth muscle cell layer of the uterus. A great number of associated complications are observed including infertility, miscarriage, bleeding, pain, dysmenorrhea, menorrhagia, and dyspareunia. Although the etiology of UL is largely undefined, environmental and genetic factors are witnessed to engage in the UL development. As long non-coding RNAs (lncRNAs) are involved in various types of cellular functions, in recent years, a great deal of attention has been drawn to them and their possible roles in UL pathogenesis. Moreover, they have illustrated their potential to be promising candidates for UL treatment. In this review paper, firstly, an overview of UL pathogenesis is presented. Then, the regulation of lncRNAs in UL and their possible mechanisms in cancer development are reviewed. Eventually, therapeutic approaches targeting lncRNAs in various cancers and UL are explored.

Angel or Devil ? - CDK8 as the new drug target

Cyclin-dependent kinase 8 (CDK8) plays an momentous role in transcription regulation by forming kinase module or transcription factor phosphorylation. A large number of evidences have identified CDK8 as an important factor in cancer occurrence and development. In addition, CDK8 also participates in the regulation of cancer cell stress response to radiotherapy and chemotherapy, assists tumor cell invasion, metastasis, and drug resistance. Therefore, CDK8 is regarded as a promising target for cancer therapy. Most studies in recent years supported the role of CDK8 as a carcinogen, however, under certain conditions, CDK8 exists as a tumor suppressor. The functional diversity of CDK8 and its exceptional role in different types of cancer have aroused great interest from scientists but even more controversy during the discovery of CDK8 inhibitors. In addition, CDK8 appears to be an effective target for inflammation diseases and immune system disorders. Therefore, we summarized the research results of CDK8, involving physiological/pathogenic mechanisms and the development status of compounds targeting CDK8, provide a reference for the feasibility evaluation of CDK8 as a therapeutic target, and guidance for researchers who are involved in this field for the first time.

Insights into the regulatory role and clinical relevance of mediator subunit, MED12, in human diseases

Transcriptional dysregulation is central to many diseases including cancer. Mutation or deregulated expression of proteins involved in transcriptional machinery leads to aberrant gene expression that disturbs intricate cellular processes of division and differentiation. The subunits of the mediator complex are master regulators of stimuli-derived transcription and are essential for transcription by RNA polymerase II. MED12 is a part of the CDK8 kinase module of the mediator complex and is essential for kinase assembly and function. Other than its function in activation of the kinase activity of CDK8 mediator, it also brings about transcription repression or activation, in response to several signalling pathways, a function that is independent of its role as a part of kinase assembly. Accumulating evidence suggests that MED12 controls complex transcription programs that are defining in cell fate determination, differentiation, and carcinogenesis. Mutations or differential expression of MED12 manifest in several human disorders and diseases. For instance, MED12 mutations are the gold standard for the diagnosis of several X-linked intellectual disability syndromes. Further, certain MED12 mutations are categorised as driver mutations in carcinogenesis as well. This is a timely review that provides for the first time a wholesome view on the critical roles and pathways regulated by MED12, its interactions along with the implications of MED12 alterations/mutations in various cancers and nonneoplastic disorders. Based on the preclinical studies, MED12 indeed emerges as an attractive novel therapeutic target for various diseases and intellectual disorders.

Molecular differential diagnosis of uterine leiomyomas and leiomyosarcomas

Uterine leiomyomas (LM) and leiomyosarcomas (LMS) are considered biologically unrelated tumors due to their cytogenetic and molecular disparity. Yet, these tumors share morphological and molecular characteristics that cannot be differentiated through current clinical diagnostic tests, and thus cannot be definitively classified as benign or malignant until surgery. Newer approaches are needed for the identification of these tumors, as has been done for other tissues. The application of next generation sequencing enables the detection of new mutations that, when coupled to machine learning bioinformatic tools, advances our understanding of chromosomal instability. These approaches in the context of LM and LMS could allow the discovery of genetic variants and possible genomic markers. Additionally, the potential clinical utility of circulating cell-free tumor DNA could revolutionize the noninvasive detection and monitoring of these tumors. Here, we seek to provide a perspective on the molecular background of LM and LMS, recognizing their distinct molecular features that may lead to improved diagnosis and personalized treatments, which would have a measurable impact on women's reproductive health.

Gene fusions characterize a subset of uterine cellular leiomyomas

Uterine leiomyomas are the most common benign tumor of the female genital tract. Previous studies have shown that conventional leiomyomas often harbor-specific alterations including rearrangements involving HMGA2. Cellular leiomyomas are a variant of uterine leiomyoma that are less well-studied from a genomic point of view. Morphologically and immunohistochemically, cellular leiomyomas may be confused with low-grade endometrial stromal neoplasms, a group of tumors which frequently harbor a number of recurrent gene fusions. Ancillary molecular testing may be used to investigate tumors where low-grade endometrial stromal neoplasms enter into the differential diagnosis. At our institution, we identified a uterine cellular leiomyoma harboring a HMGA2-TRAF3IP2 fusion. After a retrospective review 11 additional tumors were identified. All included cases were reviewed and evaluated for immunohistochemical expression of smooth muscle actin, desmin, h-caldesmon, CD10, estrogen receptor, and progesterone receptor. RNA sequencing using the TruSight RNA Fusion Panel was performed on formalin-fixed paraffin-embedded tissue samples. In addition to the index case, two other cases harbored fusions: HMGA2-NAA11 and TPCN2-YAP1, of which the latter is novel and was confirmed with reverse transcriptase-polymerase chain reaction. In conclusion, a subset of cellular leiomyomas harbor rearrangements involving HMGA2, suggesting molecular kinship with conventional uterine leiomyomas. In addition, the prevalence of the novel TPCN2-YAP1 gene fusion in cellular leiomyomas requires further study. The fusions reported here, when identified, may be useful when the diagnosis of cellular leiomyoma is in question.

MED12 exon 2 mutation is uncommon in intravenous leiomyomatosis: clinicopathologic features and molecular study

Intravenous leiomyomatosis (IVL) is a rare neoplasm that is characterized by smooth muscle cell proliferation within venous vessels. The aim of this study is to investigate the clinicopathological features, immunophenotypes, and MED12 gene mutations in IVL. Nine cases of IVL from the Affiliated Hospital of Qingdao University were collected, and the clinicopathological features were reviewed. The immunohistochemical expressions of p16, phosphatase and tensin homolog deleted on chromosome 10 (PTEN), alpha thalassemia/mental retardation syndrome X-linked (ATRX), retinoblastoma 1 (RB1), fumarate hydratase (FH), and p53, were evaluated. The mutation status of MED12 gene exon 2 was detected by Sanger sequencing. All the 9 patients were women ranging from 32 to 58 years, and uterine leiomyomas were identified in 5 patients. Immunohistochemical staining showed that all IVL and leiomyoma samples were positive for estrogen receptor and progesterone receptor, but negative for CD34. IVL displayed similar immunostaining patterns with their uterine counterparts with focal p16 immunostaining. FH, PTEN, ATRX, and RB1 were variably positive, and p53 and Ki-67 positive rates were less than 5% in all cases. Two novel genetic variations at MED12 exon 2, a synonymous mutation c.141C>T (p.Asn47=), and an in-frame deletion mutation c.133_147del15 (p.Phe45_Pro49del) were identified in two IVL cases. One missense mutation c.131G>A (p.Gly44Asp) was identified in one uterine leiomyoma. The remaining 11 tumor samples (7 IVL cases and 4 uterine leiomyomas) showed no mutations at MED12 exon 2. Our results showed two novel MED12 mutations in IVL. The MED12 mutations are different between IVL and uterine leiomyoma. These findings indicate that IVL is a unique entity and different from uterine leiomyoma.

Identification of Prognostic Genes in Leiomyosarcoma by Gene Co-Expression Network Analysis

Background/Aims

Leiomyosarcoma (LMS) is a tumor derived from malignant mesenchymal tissue associated with poor prognosis. Determining potential prognostic markers for LMS can provide clues for early diagnosis, recurrence, and treatment.

Methods

RNA sequence data and clinical features of 103 LMS were obtained from the Cancer Genome Atlas (TCGA) database. Application Weighted Gene Co-Expression Network Analysis (WGCNA) was used to construct a free-scale gene co-expression network, to study the interrelationship between its potential modules and clinical features, and to identify hub genes in the module. The hub gene function was verified by an external database.

Results

Twenty-four co-expression modules were constructed using WGCNA. A dark red co-expression module was found to be significantly associated with disease recurrence. Functional enrichment analysis and GEPIA and ONCOMINE database analyses demonstrated that hub genes CDK4, CCT2, and MGAT1 may play an important role in LMS recurrence.

Conclusion

Our study constructed an LMS co-expressing gene module and identified prognostic markers for LMS recurrence detection and treatment.

Intravenous leiomyomatosis: molecular analysis of 17 cases

Intravenous leiomyomatosis (IVL) is a rare smooth muscle tumour with a benign histology but with a quasi-malignant intravascular growth. In this study, we investigated the molecular alterations in 17 IVL cases composed of concurrent uterine leiomyoma (n=12), uterine IVL (n=17) and extra-uterine IVL (n=12). We found that eight tumours had a somatic MED12 mutation (c.130G>A, p.G44S, n=7; c.131G>C, p.G44A, n=1). The frequency of MED12 mutations was significantly higher in concurrent uterine leiomyoma (6/12, 50%) than in uterine (0/17, 0%) and extra-uterine IVL (2/12, 16.7%). The frequency of HMGA2 over-expression or MED12 low-expression was not significantly different among uterine leiomyoma, IVL and extra-uterine IVL (p>0.05). Short tandem repeat (STR) analysis indicated that one uterine and two extra-uterine IVL tumours from three patients were microsatellite instability positive (MSI+) whereas loss of heterozygosity (LOH) was found in one uterine leiomyoma, three uterine and three extra-uterine IVL tumours from five patients. LOH was more frequently seen in uterine/extra-uterine IVL tumours (6/20, 30%) than in the concurrent leiomyomas (1/7, 14.3%) (p<0.05). MED12 mutation, MSI and LOH were discordant between uterine and extra-uterine IVL in all patients. These findings suggest that IVL harbours distinct molecular pathogenesis from common uterine leiomyomas. Uterine IVL and extra-uterine tumours may represent an independent origin rather than uniclonal dissemination from a single tumour. Further investigations are warranted to explore the underlying key molecular events in the pathogenesis of IVL.

Immunofluorescence analysis of DNA damage response protein p53-binding protein 1 in a case of uterine dedifferentiated leiomyosarcoma arising from leiomyoma

AIMS

Genomic instability has been indicated during the dedifferentiation process from leiomyoma (LM) to leiomyosarcoma (LMS). Previously, we have described that nuclear expression pattern of DNA damage response protein p53-binding protein 1 (53BP1), detected by immunofluorescence, reflects the magnitude of genomic instability during malignancy. Here, we present a case of LMS arising from LM with molecular analysis of 53BP1, which showed transitional magnitude of DNA damage response within a tumor.

METHODS AND RESULTS

A fifty-year-old female with abdominal mass underwent hysterectomy. Histologically, the tumor consisted of LMS with highly atypical multinucleated giant cells as well as an LM component with transitional atypical spindle cells in the border area. LMS showed diffuse nuclear staining of 53BP1 expression, which has been previously described as high DNA damage response pattern. In contrast, the LM component lacked 53BP1 immunoreactivity and focal expression was observed in transitional lesion. Furthermore, double-labelled immunofluorescence revealed co-localization of 53BP1 with p53 and Ki-67 in the LMS component, which indicated abnormal DNA damage response in proliferative state.

CONCLUSIONS

This study revealed that diffuse-type 53BP1 expression may be beneficial to estimate genomic instability during dedifferentiation from LM to DLMS.

LncRNA SRA1 may play a role in the uterine leiomyoma tumor growth regarding the MED12 mutation pattern

Background

Uterine leiomyomas (ULMs) are benign uterine tumors that are estrogen-dependent. Recent studies suggest that the abnormal expression of the steroid receptor RNA activator 1 (SRA1) long non-coding RNA (lncRNA) might participate in the mechanisms of tumorigenesis of some hormone-dependent tumors including breast cancer. SRA1 is known to enhance the transcriptional activity of steroid receptors and also promotes steroidogenesis. The level of steroid hormones, such as estrogen and the progesterone, and their receptors play an important role in the development and growth of leiomyoma. The aim of the present study was to determine the expression level of lncRNA SRA1 in ULM tissues considering the MED12 mutation pattern.

Methods

Mutation screening was performed for MED12 exons 1 and 2 and the intronic flanking regions using Sanger sequencing in 60 ULM tissues. Quantitative real-time polymerase chain reaction (qRT-PCRs) was performed in order to estimate the expression of lncRNA SRA1 in leiomyoma samples with and without MED12 gene mutations. The expression results were analyzed by using LinReg and REST software.

Results

Mutations were detected in exon 2 of the MED12 in 28 (46.67%) ULM samples; including, 21 (75%) missense mutations and 7 (25%) in-frame deletions. No mutation was detected in the MED12 exon 1. LncRNA SRA1 was over-expressed in ULM samples without MED12 mutation compared with ULM samples harboring MED12 mutation (Expression ratio=2.5, P-value=0.004).

Conclusion

Present results suggest that lncRNA SRA1 may explain the phenotypic difference observed in the tumor size of ULM samples considering MED12 mutation pattern. Therefore, it serves as a good therapeutic target and provides new insight into understanding the disease molecular mechanism.

Identifying Cancers Impacted by CDK8/19

CDK8 and CDK19 Mediator kinases are transcriptional co-regulators implicated in several types of cancer. Small-molecule CDK8/19 inhibitors have recently entered or are entering clinical trials, starting with breast cancer and acute myeloid leukemia (AML). To identify other cancers where these novel drugs may provide benefit, we queried genomic and transcriptomic databases for potential impact of CDK8, CDK19, or their binding partner CCNC. sgRNA analysis of a panel of tumor cell lines showed that most tumor types represented in the panel, except for some central nervous system tumors, were not dependent on these genes. In contrast, analysis of clinical samples for alterations in these genes revealed a high frequency of gene amplification in two highly aggressive subtypes of prostate cancer and in some cancers of the GI tract, breast, bladder, and sarcomas. Analysis of survival correlations identified a group of cancers where CDK8 expression correlated with shorter survival (notably breast, prostate, cervical cancers, and esophageal adenocarcinoma). In some cancers (AML, melanoma, ovarian, and others), such correlations were limited to samples with a below-median tumor mutation burden. These results suggest that Mediator kinases are especially important in cancers that are driven primarily by transcriptional rather than mutational changes and warrant an investigation of their role in additional cancer types.

Pleomorphic Undifferentiated Uterine Sarcoma in a Young Patient Presenting With Elevated Beta-hCG and Rare Variants of Benign Leiomyoma: A Case Report and Review of the Literature

Leiomyosarcoma (LMS) is a malignant mesenchymal neoplasm showing smooth muscle differentiation. Uterine LMS is more frequent that nonuterine LMS, and represents 1% of all malignant neoplasms of the uterus. Pleomorphic undifferentiated uterine sarcoma is a rare entity, and is defined by high-grade sarcoma histology with loss of muscular markers. Several cases of pleomorphic undifferentiated uterine sarcoma have been reported in the literature, with worse clinical outcome when compared with conventional LMS. Here we report the first case of a pleomorphic undifferentiated uterine sarcoma in association with LMS in a 33 yr old woman. The patient presented clinically with recurrent vaginal bleeding and suspicion of a trophoblastic tumor. Ancillary testing revealed moderately elevated beta-hCG (49.7 U/L) and no metastatic disease on imaging. Gross examination of the hysterectomy specimen revealed a large heterogenous necrotic uterine mass infiltrating <50% of the myometrium. Microscopic evaluation showed pleomorphic undifferentiated uterine sarcoma adjacent to a nodule of leiomyoma with bizarre nuclei, with loss of myogenic markers in the high grade component. Other findings included a foci of conventional LMS, and diffuse uterine leiomyomatosis. Although beta-hCG dropped to normal levels during follow-up, the patient developed metastatic lesions to the lung at 6 mo postop. Initial elevation of beta-hCG may have correlated with the aggressive histology of the tumor, as reported by some groups previously. Recognition of pleomorphic undifferentiated uterine sarcoma and its distinction from conventional LMS is essential for patient prognosis and management.

Understanding Obesity as a Risk Factor for Uterine Tumors Using Drosophila

Multiple large-scale epidemiological studies have identified obesity as an important risk factor for a variety of human cancers, particularly cancers of the uterus, gallbladder, kidney, liver, colon, and ovary, but there is much uncertainty regarding how obesity increases the cancer risks. Given that obesity has been consistently identified as a major risk factor for uterine tumors, the most common malignancies of the female reproductive system, we use uterine tumors as a pathological context to survey the relevant literature and propose a novel hypothesis: chronic downregulation of the cyclin-dependent kinase 8 (CDK8) module, composed of CDK8 (or its paralog CDK19), Cyclin C, MED12 (or MED12L), and MED13 (or MED13L), by elevated insulin or insulin-like growth factor signaling in obese women may increase the chances to dysregulate the activities of transcription factors regulated by the CDK8 module, thereby increasing the risk of uterine tumors. Although we focus on endometrial cancer and uterine leiomyomas (or fibroids), two major forms of uterine tumors, our model may offer additional insights into how obesity increases the risk of other types of cancers and diseases. To illustrate the power of model organisms for studying human diseases, here we place more emphasis on the findings obtained from Drosophila melanogaster.

Mediator Kinase Disruption in MED12-Mutant Uterine Fibroids From Hispanic Women of South Texas

CONTEXT

Mutations in the gene encoding Mediator complex subunit MED12 are dominant drivers of uterine fibroids (UFs) in women of diverse racial and ethnic origins. Previously, we showed that UF-linked mutations in MED12 disrupt its ability to activate cyclin C-CDK8/19 in Mediator. However, validation of Mediator kinase disruption in the clinically relevant setting of MED12-mutant UFs is currently lacking.

OBJECTIVE

The objective of this study was twofold. First, to extend the ethnic distribution profile of MED12 mutations by establishing their frequency in UFs from Hispanic women of South Texas. Second, to examine the impact of MED12 mutations on Mediator kinase activity in patient-derived UFs.

METHODS

We screened 219 UFs from 76 women, including 170 tumors from 57 Hispanic patients, for MED12 exon 2 mutations, and further examined CDK8/19 activity in Mediator complexes immunoprecipitated from MED12 mutation-negative and MED12 mutation-positive UFs.

RESULTS

MED12 exon 2 mutations in UFs from Hispanic women are somatic in nature, predominantly monoallelic, and occur at high frequency (54.1%). We identified a minimal cyclin C-CDK8 activation domain on MED12 spanning amino acids 15 through 80 that includes all recorded UF-linked mutations in MED12, suggesting that disruption of Mediator kinase activity is a principal biochemical defect arising from these pathogenic alterations. Analysis of Mediator complexes recovered from patient UFs confirmed this, revealing that Mediator kinase activity is selectively impaired in MED12-mutant UFs.

CONCLUSIONS

MED12 mutations are important drivers of UF formation in Hispanic women of South Texas. MED12 mutations disrupt Mediator kinase activity, implicating altered CDK8/19 function in UF pathogenesis.

MED12 is recurrently mutated in Middle Eastern colorectal cancer

OBJECTIVE

Colorectal cancer (CRC) is a common cancer and a leading cause of cancer deaths. Previous studies have identified a number of key steps in the evolution of CRC but our knowledge of driver mutations in CRC remains incomplete. Recognising the potential of studying different human populations to reveal novel insights in disease pathogenesis, we conducted genomic analysis of CRC in Saudi patients.

DESIGN

In the discovery phase of the study, we conducted whole genome sequencing of tumour and corresponding germline DNA in 27 patients with CRC. In addition to known driver mutations, we identified three MED12 somatic mutations. In the replication phase, we employed a next-generation sequencing approach to capture and sequence MED12 and other candidate genes in a larger sample of 400 patients with CRC and confirmed the enrichment for recurrent MED12 mutations.

RESULTS

In order to gain insight into a plausible biological mechanism for the potential role of MED12 mutations in CRC, we studied CRC cell lines that differ substantially in the expression level of MED12, and found the latter to be correlated inversely with transforming growth factor (TGF)-β signalling and directly with apoptosis in response to chemotherapeutic agents. Importantly, these correlations were replicated when MED12 expression was experimentally manipulated.

CONCLUSIONS

Our data expand the recently described role of MED12 as a tumour suppressor in other cancers to include CRC, and suggest TGF-β signalling as a potential mediator of this effect.

Clinical, pathologic, cytogenetic, and molecular profiling in self-identified black women with uterine leiomyomata

Black women are disproportionately affected by uterine leiomyomata (UL), or fibroids, compared to other racial groups, having a greater lifetime risk of developing UL and an earlier age of diagnosis. In order to elucidate molecular and genetic mechanisms responsible for the increased prevalence and morbidity associated with UL in black women, clinical, pathologic, cytogenetic, and select molecular profiling (MED12 mutation analysis) of 75 self-reported black women undergoing surgical treatment for UL was performed. Our observations are broadly representative of previous cytogenetic studies of UL: karyotypically abnormal tumors were detected in 30.7% of women and 17.4% of analyzed tumors. No notable association was observed between race and increased occurrence of cytogenetic abnormalities that might contribute to any population-specific morbidity or prevalence rate. Our data on MED12 mutation analyses (73.2% of tumors harbored a MED12 mutation) provide additional support for a significant role of MED12 in tumorigenesis. Although the effect of MED12-mediated tumorigenesis appears significant irrespective of race, other genetic events such as the distribution of karyotypic abnormalities appear differently in black women. This case series indicates that presently recognized genetic and molecular characteristics of UL do not appear to explain the increased prevalence and morbidity of UL in black women.

Multiple clinical characteristics separate MED12-mutation-positive and -negative uterine leiomyomas

Up to 86% of uterine leiomyomas harbour somatic mutations in mediator complex subunit 12 (MED12). These mutations have been associated with conventional histology, smaller tumour size, and larger number of tumours within the uterus. Prior studies, with limited sample sizes, have failed to detect associations between other clinical features and MED12 mutations. Here, we prospectively collected 763 uterine leiomyomas and the corresponding normal myometrial tissue from 244 hysterectomy patients, recorded tumour characteristics, collected clinical data from medical records, and screened the tissue samples for MED12 mutations to assess potential associations between clinical variables and mutation status. Out of 763 leiomyomas, 599 (79%) harboured a MED12 mutation. In the analysis of tumour characteristics, positive MED12-mutation status was significantly associated with smaller tumour size, conventional histology, and subserous location, relative to intramural. In the analysis of clinical variables, the number of MED12-mutation-positive tumours showed an inverse association with parity, and the number of mutation-negative tumours showed a positive association with a history of pelvic inflammatory disease. This study confirmed the previously reported differences and discovered novel differentiating features for MED12-mutation-positive and -negative leiomyomas. These findings emphasise the relevance of specific driver mutations in genesis and presentation of uterine leiomyomas.

Identification of uterine leiomyoma-specific marker genes based on DNA methylation and their clinical application

Differential diagnosis of uterine leiomyomas and leiomyosarcomas is needed to determine whether the uterus can be retained. Therefore, biomarkers for uterine leiomyomas, and reliable and objective diagnostic methods have been desired besides the pathological diagnosis. In the present study, we identified 12 genes specific to uterine leiomyomas based on DNA methylation. Using these marker genes specific to uterine leiomyomas, we established a hierarchical clustering system based on the DNA methylation level of the marker genes, which could completely differentiate between uterine leiomyomas and normal myometrium. Furthermore, our hierarchical clustering system completely discriminated uterine cancers and differentiated between uterine leiomyosarcomas and leiomyomas with more than 70% accuracy. In conclusion, this study identified DNA methylation-based marker genes specific to uterine leiomyomas, and our hierarchical clustering system using these marker genes was useful for differential diagnosis of uterine leiomyomas and leiomyosarcomas.

Targeting leiomyomas with all-trans-retinoic acid at phosphoinositide 3-kinase pathway suppression: Effective roles of β-catenin and of signaling interactions

AIM

Leiomyomas, monoclonal tumors developed by the transformation of myometrium somatic stem cells, are a major health concern that can severely impair quality of life. Pathological alterations of signaling pathways have been recognized as a key feature in a variety of human diseases. Our objective was to analyze treatment with all-trans-retinoic acid (ATRA) by suppression of the phosphoinositide 3-kinase (PI3K) pathway on growth, signaling pattern and interactions among PI3K/B-cell lymphoma 2 (Bcl2)/retinol leiomyoma proteins.

METHODS

Cultures of paired myometrium and leiomyoma cells from premenopausal women undergoing hysterectomy were collected. Western blot and analysis of variance were used for analysis.

RESULTS

Significant differences were detected between treatment with ATRA alone or with LY294002 (a PI3K growth suppressor) in response to treatment and among cell samples and cell numbers. Leiomyoma cells were less affected. Immunochemical analysis of signaling patterns demonstrated that treatments affected most of the examined protein levels differently. Significant differences between the cell type responses to treatment in pyruvate phosphate dikinase 1 (pPDK1), Bad and pβ-catenin levels were identified. The pβ-catenin level showed highly significant interaction between response to treatment and cell type.

CONCLUSIONS

ATRA treatment on PI3K pathway suppression significantly affected growth, signaling pattern and interactions among PI3K/Bcl2/retinol proteins involved in the growth, survival and apoptosis of leiomyomas. Interpretation of our results suggests that increasing knowledge of the role of signaling interplay in the pathogenesis of leiomyomas may present an opportunity to use specific signal transduction inhibitors for treating and preventing this disorder.

Phyllodes tumours of the breast: a consensus review

Phyllodes tumours constitute an uncommon but complex group of mammary fibroepithelial lesions. Accurate and reproducible grading of these tumours has long been challenging, owing to the need to assess multiple stratified histological parameters, which may be weighted differently by individual pathologists. Distinction of benign phyllodes tumours from cellular fibroadenomas is fraught with difficulty, due to overlapping microscopic features. Similarly, separation of the malignant phyllodes tumour from spindle cell metaplastic carcinoma and primary breast sarcoma can be problematic. Phyllodes tumours are treated by surgical excision. However, there is no consensus on the definition of an appropriate surgical margin to ensure completeness of excision and reduction of recurrence risk. Interpretive subjectivity, overlapping histological diagnostic criteria, suboptimal correlation between histological classification and clinical behaviour and the lack of robust molecular predictors of outcome make further investigation of the pathogenesis of these fascinating tumours a matter of active research. This review consolidates the current understanding of their pathobiology and clinical behaviour, and includes proposals for a rational approach to the classification and management of phyllodes tumours.

Practical issues in uterine pathology from banal to bewildering: the remarkable spectrum of smooth muscle neoplasia

Among mesenchymal tumors of the uterus, smooth muscle neoplasms are most common. The wide morphologic spectrum, especially within the category of leiomyomas, is responsible for diagnostic problems more frequently with leiomyosarcoma (including mitotically active, apoplectic, and leiomyoma with bizarre nuclei) but also with endometrial stromal tumors. In the former scenario, clinical information, gross appearance as well as strict utilization of morphologic criteria including cytologic atypia, mitotic activity, and tumor cell necrosis are clues in establishing the correct diagnosis. It is important to keep in mind that mitotic rate thresholds vary for the different subtypes of leiomyosarcoma. Of note, p16 should be used with caution in supporting a diagnosis of leiomyosarcoma as it is often positive in leiomyomas with bizarre nuclei and leiomyomas with apoplectic change (in the latter most frequently and more intense near areas of necrosis). MED12 mutations have also a very limited role in this differential diagnosis. Endometrial stromal tumors are by far, less common than smooth muscle tumors, but can be confused with leiomyosarcomas if they are associated with an undifferentiated uterine sarcoma and the low-grade component is overlooked or they have a myxoid/fibroblastic morphology. The differential diagnosis may be confounded if the latter is associated with a high-grade endometrial stromal sarcoma. It is important to highlight that CD10 is not a reliable marker in these differentials and should be used as a part of a panel of antibodies that also includes desmin and h-caldesmon. Two other recently categorized tumors in the uterus that merit special mention are PEComa and inflammatory myofibroblastic tumor as they enter in the differential diagnosis of smooth muscle tumors. PEComa may be part of the tuberous sclerosis syndrome and may show either a predominantly epithelioid or spindle morphology or combination thereof. Rarely, it may contain melanin pigment. There is variable positivity for HMB-45, MelanA, MiTF, and CathepsinK, and some tumors have been shown to express TFE-3 especially when associated with "clear cell" morphology. Patients with adverse outcome have tumors with ≥2 of the following features: ≥5 cm, infiltration, high-grade cytologic features, mitotic rate ≥1/50 high-power fields, necrosis, or lymphovascular invasion. Inflammatory myofibroblastic tumor is important to recognize as it often mimics myxoid smooth muscle tumors, either benign or malignant. The presence of an associated lymphoplasmacytic infiltrate should alert to that possibility and ALK studies (immunostain or FISH) are helpful in establishing this diagnosis. These tumors can behave in a malignant manner if large, associated with abundant myxoid change, brisk mitotic rate or show tumor cell necrosis.