SOX10-Internal Tandem Duplications and PLAG1 or HMGA2 Fusions Segregate Eccrine-Type and Apocrine-Type Cutaneous Mixed Tumors

Cutaneous mixed tumors exhibit a wide morphologic diversity and are currently classified into apocrine and eccrine types based on their morphologic differentiation. Some cases of apocrine-type cutaneous mixed tumors (ACMT), namely, hyaline cell-rich apocrine cutaneous mixed tumors (HCR-ACMT) show a prominent or exclusive plasmacytoid myoepithelial component. Although recurrent fusions of PLAG1 have been observed in ACMT, the oncogenic driver of eccrine-type cutaneous mixed tumors (ECMT) is still unknown. The aim of the study was to provide a comprehensive morphologic, immunohistochemical, and molecular characterization of these tumors. Forty-one cases were included in this study: 28 cases of ACMT/HCR-ACMT and 13 cases of ECMT. After morphologic and immunohistochemical characterization, all specimens were analyzed by RNA sequencing. By immunohistochemistry, all cases showed expression of SOX10, but only ACMT/HCR-ACMT showed expression of PLAG1 and HMGA2. RNA sequencing confirmed the presence of recurrent fusion of PLAG1 or HMGA2 in all cases of ACMT/HCR-ACMT, with a perfect correlation with PLAG1/HMGA2 immunohistochemical status, and revealed internal tandem duplications of SOX10 (SOX10-ITD) in all cases of ECMT. Although TRPS1::PLAG1 was the most frequent fusion, HMGA2::WIF1 and HMGA2::NFIB were detected in ACMT cases. Clustering analysis based on gene expression profiling of 110 tumors, including numerous histotypes, showed that ECMT formed a distinct group compared with all other tumors. ACMT, HCR-ACMT, and salivary gland pleomorphic adenoma clustered together, whereas myoepithelioma with fusions of EWSR1, FUS, PBX1, PBX3, POU5F1, and KLF17 formed another cluster. Follow-up showed no evidence of disease in 23 cases across all 3 tumor types. In conclusion, our study demonstrated for the first time SOX10-ITD in ECMT and HMGA2 fusions in ACMT and further refined the prevalence of PLAG1 fusions in ACMT. Clustering analyses revealed the transcriptomic distance between these different tumors, especially in the heterogenous group of myoepitheliomas.

Pleomorphic Adenoma with a Novel Gene Rearrangement-LINC01606::PLAG1

BACKGROUND

Pleomorphic adenoma is a well-known benign salivary gland neoplasm characterized by the presence of varying proportions of three different components, including bi-layered ducts, myoepithelial cells, and admixed within a chondromyxoid/fibrous stroma.

METHOD

We report an interesting case of an adult male who presented with bleeding from an extensively degenerated parotid gland mass, concerning for a vascular neoplasm versus primary malignant tumor. Microscopically, majority of the viable tumor exhibited diffuse proliferation of spindle to epithelioid cells, with focal areas depicting cribriform glands, ducts, and scant chondromyxoid stroma.

RESULT

Next-generation sequencing (NGS) RNA-based fusion panel analysis identified a gene rearrangement involving the pleomorphic adenoma gene 1 (PLAG1), with a novel, cryptogenic fusion partner known as LINC01606; [LINC01606::PLAG1; inv(8;8)(8q12.1;8q12.1)].

CONCLUSION

To the best of our knowledge, this is the first documented case of a long non-coding RNA (lnc-RNA) serving as a rearrangement partner with the PLAG1 gene. We reviewed the molecular characteristics of this entity and explored the potential role of LINC01606::PLAG1 in the tumorigenesis of pleomorphic adenoma.

Circular RNA CircACAP2 regulates temporomandibular joint osteoarthritis via miR-21-5p/PLAG1 axis

OBJECTIVES

The pathogenesis of temporomandibular joint osteoarthritis (TMJOA) remains not fully understood. Our previous studies demonstrated that miR-21-5p may participate in the TMJOA development and the interaction between circRNA-ACAP2 (CircACAP2) and miR-21-5p. Our present study aimed to explore the biological functions and regulatory mechanisms of CircACAP2 in TMJOA.

MATERIALS AND METHODS

The differential expression pattern of CircACAP2 in OA and normal tissues or cells was detected. CircACAP2 biological functions experiments were performed in chondrocytes by overexpression and interference techniques. The interaction of CircACAP2 with miR-21-5p and downstream target mRNA, polymorphic adenoma gene 1 (PLAG1), was predicted by bioinformatic databases and then demonstrated by dual-luciferase reporter assay. The biological role of CircACAP2 in TMJOA was investigated and validated in a mouse model.

RESULTS

The expression level of CircACAP2 was markedly reduced in OA cartilage and directly related to chondrocyte proliferation and apoptosis as well as ECM metabolism in the cartilage. CircACAP2 functioned in chondrocytes via targeting miR-21-5p and PLAG1. Overexpressing of CircACAP2 alleviated TMJOA in mouse models.

CONCLUSIONS

The present study unveiled that CircACAP2/miR-21-5p/PLAG1 axis may play an important regulatory role in TMJOA progression, which may highlight a potentially effective intervention and therapeutic strategy for the treatment of TMJOA.

[Supratentorial neuroepithelial tumor with PLAGL1 gene fusion - a new type of morphologically variable pediatric brain neoplasm defined by a distinct DNA methylation class. A case report and literature review]

BACKGROUND

Methylation analysis has become a powerful diagnostic tool in modern neurooncology. This technique is valuable to diagnose new brain tumor types.

OBJECTIVE

To describe the MRI and histological pattern of neuroepithelial tumor with PLAGL1 gene fusion.

MATERIAL AND METHODS

We present a 6-year-old patient with small right frontal intraaxial tumor causing drug resistant epilepsy. Despite indolent preoperative clinical course and MRI features suggesting glioneuronal tumor, histological evaluation revealed characteristics of high-grade glioma, ependymoma and neuroblastoma.

RESULTS

Methylation analysis of tumor DNA confirmed a new type of a recently discovered neoplasm - neuroepithelial tumor with PLAGL1 fusion (NET PLAGL1). PCR confirmed fusion of PLAGL1 and EWSR1 genes. No seizures were observed throughout the follow-up period. There was no tumor relapse a year after surgery.

CONCLUSION

Methylation analysis in neurooncology is essential for unclear tumor morphology or divergence between histological and clinical data. In our case, this technique confirmed benign nature of tumor, and we preferred follow-up without unnecessary adjuvant treatment.

Chromothripsis in lipoblastoma: second reported case with complex PLAG1 rearrangement

Lipoblastomas (LPBs) are rare benign neoplasms derived from embryonal adipose that occur predominantly in childhood. LPBs typically present with numeric or structural rearrangements of chromosome 8, the majority of which involve the pleomorphic adenoma gene 1 (PLAG1) proto-oncogene on chromosome 8q12. Here, we report on a LPB case on which showed evidence of chromothripsis. This is the second reported case of chromothripsis in LPB.

[Myoepithelial tumors of soft tissue: A case of mixed tumor]

Myoepithelial neoplasms of soft tissue represent a rare entity which has been described only recently when compared to salivary gland tumors with whom they share histopathological and molecular features. The most common locations are the superficial soft tissues of the limbs and limb girdles. However, they can rarely occur in the mediastinum, abdomen, bone, skin and visceral organs. Benign forms (myoepithelioma and mixed tumor) are more frequent than myoepithelial carcinoma and the latter mostly affects children and young adults. Diagnosis is mainly based on histology, which shows a proliferation of myoepithelial cells of variable morphology with or without glandular structures in a myxoid background, and immunohistochemistry, which shows co-expression of epithelial and myoepithelial markers. Molecular tests are not mandatory, but in selected cases FISH analysis can prove useful as about 50% of myoepitheliomas show EWSR1 (or rarely FUS) rearrangements and mixed tumors show PLAG1 rearrangements. Here, we present a case of a mixed tumor of the soft tissue occuring in the hand with expression of PLAG1 in immunohistochemistry.

Clinical characterization of PLAG1- related Silver-Russell syndrome：A clinical report

BACKGROUND

Silver-Russell syndrome (SRS) is a rare genetic disorder that is mainly associated with prenatal and postnatal growth retardation. Loss of methylation on chromosome 11p15 and maternal uniparental disomy on chromosome 7 (upd(7)mat) are two common causes, accounting for approximately 50% and 10% of all patients, respectively. Pathogenic variants of genes, such as HMGA2, IGF2, CDKN1C, and PLAG1, have also been detected in patients with SRS. So far, SRS caused by PLAG1 alterations have only been described in two sporadic cases and three families.

PATIENT PRESENTATION

The genetic and clinical manifestations of SRS in a patient carrying a novel variant of PLAG1 were reported and these results were compared with those of five previously reported cases. Trio-based whole-exome sequencing revealed a heterozygous variation in PLAG1 (NM_002655.3: c.131del; p.(Asn44Thrfs*6)) in an infant girl with clinical suspicion of SRS. Familial studies confirmed that the mutation was inherited from her father. As seen in previously reported cases, the patient presented with prenatal and postnatal growth retardation, relative macrocephaly at birth, prominent forehead during infancy, and triangular face. However, no clinical characteristics such as feeding difficulties, hypothyroidism, or psychomotor and speech delay.

CONCLUSIONS

This study identified the sixth documented case of PLAG1 variants leading to SRS and expanded our knowledge of the molecular spectrum of SRS phenotypes.

Lipoblastoma Arising in the Head and Neck: A Clinicopathologic Analysis of 20 Cases

BACKGROUND

Lipoblastomas (LPBs) are benign adipocytic neoplasms believed to recapitulate the development of embryonal fat.

METHODS

We investigated the clinicopathologic and immunohistochemical features of 20 lipoblastomas arising in the head and neck in 18 patients.

RESULTS

Patients included 6 males and 12 females (1:2 ratio) with age at diagnosis ranging from 4 months to 28 years. Tumors occurred more commonly in the neck (12, 66.7%) and less commonly in the forehead, scalp, and tongue (2, 11.1%). Tumor size ranged from 1.4 to 6.0 cm (median 5.0 cm). Two patients, a 4-month-old female and 3-year-old male, had local recurrence of neck tumors at 4 months and 3 years after excision, respectively. Microscopically, tumors had a lobulated growth pattern and consisted of adipocytes at varying stages of differentiation. In addition to the classical histologic features, lipoma-like and myxoid variants constituted 45% of cases. Metaplastic elements, including brown fat and cartilage, were identified in two cases.

CONCLUSIONS

LPBs arising in the head and neck region are not uncommon and occurred at a rate of 9% in our cohort. They should be kept in the differential diagnosis when a fatty tumor is encountered in an older child or occurring at an unusual location.

Ectopic PLAG1 induces muscular dystrophy in the mouse

Even though various genetic mutations have been identified in muscular dystrophies (MD), there is still a need to understand the biology of MD in the absence of known mutations. Here we reported a new mouse model of MD driven by ectopic expression of PLAG1. This gene encodes a developmentally regulated transcription factor known to be expressed in developing skeletal muscle, and implicated as an oncogene in certain cancers including rhabdomyosarcoma (RMS), an aggressive soft tissue sarcoma composed of myoblast-like cells. By breeding loxP-STOP-loxP-PLAG1 (LSL-PLAG1) mice into the MCK-Cre line, we achieved ectopic PLAG1 expression in cardiac and skeletal muscle. The Cre/PLAG1 mice died before 6 weeks of age with evidence of cardiomyopathy significantly limiting left ventricle fractional shortening. Histology of skeletal muscle revealed dystrophic features, including myofiber necrosis, fiber size variation, frequent centralized nuclei, fatty infiltration, and fibrosis, all of which mimic human MD pathology. QRT-PCR and Western blot revealed modestly decreased Dmd mRNA and dystrophin protein in the dystrophic muscle, and immunofluorescence staining showed decreased dystrophin along the cell membrane. Repression of Dmd by ectopic PLAG1 was confirmed in dystrophic skeletal muscle and various cell culture models. In vitro studies showed that excess IGF2 expression, a transcriptional target of PLAG1, phenocopied PLAG1-mediated down-regulation of dystrophin. In summary, we developed a new mouse model of a lethal MD due to ectopic expression of PLAG1 in heart and skeletal muscle. Our data support the potential contribution of excess IGF2 in this model. Further studying these mice may provide new insights into the pathogenesis of MD and perhaps lead to new treatment strategies.

Salivary carcinosarcoma: insight into multistep pathogenesis indicates uniform origin as sarcomatoid variant of carcinoma ex pleomorphic adenoma with frequent heterologous elements

AIMS

The formal pathogenesis of salivary carcinosarcoma (SCS) remained unclear, both with respect to the hypothetical development from either preexisting pleomorphic adenoma (PA) or de novo and the clonal relationship between highly heterogeneous carcinomatous and sarcomatous components.

METHODS AND RESULTS

We performed clinicopathological and molecular (targeted RNA sequencing) analyses on a large series of 16 cases and combined this with a comprehensive literature search (111 cases). Extensive sampling (average 11.6 blocks), combined with immunohistochemistry and molecular studies (PA-specific translocations including PLAG1 or HMGA2 proven in 6/16 cases), enabled the morphogenetic identification of PA in 15/16 cases (93.8%), by far surpassing a reported rate of 49.6%. Furthermore, we demonstrated a multistep (intraductal/intracapsular/extracapsular) adenoma-carcinoma-sarcoma-progression, based on two alternative histogenetic pathways (intraductal, 56.3%, versus myoepithelial pathway, 37.5%). Thereby, early intracapsular stages are identical to conventional carcinoma ex PA, while later extracapsular stages are dominated by secondary, frequently heterologous sarcomatous transformation with often large tumour size (>60 mm).

CONCLUSION

Our findings strongly indicate that SCS (almost) always develops from PA, with a complex multistep adenoma-carcinoma-sarcoma-sequence, based on two alternative histogenetic pathways. The findings from this novel approach strongly suggest that SCS pathogenetically is a rare (3-6%), unique, and aggressive variant of carcinoma ex PA with secondary sarcomatous overgrowth. In analogy to changes of terminology in other organs, the term "sarcomatoid carcinoma ex PA with/without heterologous elements" might be more appropriate.

PLAG1 g.8795C>T Mutation Regulates Early Body Weight in Hu Sheep by Weakening miR-139 Binding

Sheep birth and weaning weights indicate their growth and survival. Thus, identifying molecular genetic markers for early body weight is important in sheep breeding. Pleomorphic adenoma gene 1 (PLAG1) is important for regulating birth weight and body length in mammals; however, its relationship with sheep body weight remains unknown. Here, the 3'-untranslated region (3'-UTR) of the Hu sheep PLAG1 gene was cloned, single nucleotide polymorphisms (SNPs) were screened, genotype-early body weight relationships were analyzed, and the possible molecular mechanism was explored. PLAG1 3'-UTR sequences with five forms of base sequences plus poly(A) tails were detected in Hu sheep and the g.8795C>T mutation was identified. Luciferase reporter assay indicated that the g.8795C>T mutation influenced PLAG1 post-transcriptional activity. miRBase prediction showed that the g.8795C>T mutation was located in the miR-139 seed sequence binding region, and miR-139 overexpression significantly decreased both PLAG1-CC and PLAG1-TT activities. Moreover, the luciferase activity of PLAG1-CC was significantly lower than that of the PLAG1-TT, but miR-139 inhibition substantially increased both PLAG1-CC and PLAG1-TT luciferase activities, suggesting that PLAG1 is the target gene of miR-139. Thus, the g.8795C>T mutation upregulates PLAG1 expression by weakening its binding with miR-139, promoting PLAG1 expression, and increasing Hu sheep birth and weaning weights.

Lipoblastoma in one adult and 35 pediatric patients: Retrospective analysis of 36 cases

Lipoblastoma is a rare benign mesenchymal neoplasm that typically occurs at various sites in infants and children but may also occur in adults. Thus, differential diagnoses are often performed. To understand this tumor type, the present study described clinicopathological features, diagnosis and differential diagnosis of different morphological lipoblastomas. A single-institution retrospective review of 36 lipoblastoma cases diagnosed between 2015 and 2021 was performed. Formalin-fixed paraffin-embedded tissue was used for S-100, CD34, P16 and desmin immunohistochemistry analysis, along with rapid fluorescence in situ hybridization (FISH) detection with pleiomorphic adenoma gene 1 (PLAG1). The 36 cases included 14 females and 22 males [age range, 7 days to 33 years (median, 16.5 years); 28 patients were aged ≤3 years] and the tumors were located in the trunk (n=16), limbs (n=12), head and neck (n=6), and perineum (n=2). Histologically, lipoblastomas were divided into classic (n=15), lipoma-like (n=13) and myxoid (n=8) subtypes. They comprised lobules of mature adipose tissue of varying size and a fine capillary network surrounded by mucinous stroma. Single- or multivesicular lipoblasts positive for S-100 (29/36, 81%) were observed, with occasional mature adipocytes. Peripheral vessels and cytoplasm of primitive mesenchymal cells were diffusely positive for CD34 (36/36, 100%), whereas primitive mesenchymal cells and striated muscle tissue were positive for desmin (26/36, 72%). Most tumor cells were negative while only few were positive for P16 (8/36, 22%). FISH revealed PLAG1 breakage and rearrangement in 24/32 (75%) patients. In total, 28 patients were followed up post-operatively (range, 2-84 months; median, 41 months; 3 patients relapsed and 8 were lost to follow-up). In conclusion, diagnosis of a typical lipoblastoma is not difficult and PLAG1 breakage detection is key for the diagnosis.

Chromosome Translocations, Gene Fusions, and Their Molecular Consequences in Pleomorphic Salivary Gland Adenomas

Salivary gland tumors are a heterogeneous group of tumors originating from the major and minor salivary glands. The pleomorphic adenoma (PA), which is the most common subtype, is a benign lesion showing a remarkable morphologic diversity and that, upon recurrence or malignant transformation, can cause significant clinical problems. Cytogenetic studies of >500 PAs have revealed a complex and recurrent pattern of chromosome rearrangements. In this review, we discuss the specificity and frequency of these rearrangements and their molecular/clinical consequences. The genomic hallmark of PA is translocations with breakpoints in 8q12 and 12q13-15 resulting in gene fusions involving the transcription factor genes PLAG1 and HMGA2. Until recently, the association between these two oncogenic drivers was obscure. Studies of the Silver−Russel syndrome, a growth retardation condition infrequently caused by mutations in IGF2/HMGA2/PLAG1, have provided new clues to the understanding of the molecular pathogenesis of PA. These studies have demonstrated that HMGA2 is an upstream regulator of PLAG1 and that HMGA2 regulates the expression of IGF2 via PLAG1. This provides a novel explanation for the 8q12/12q13-15 aberrations in PA and identifies IGF2 as a major oncogenic driver and therapeutic target in PA. These studies have important diagnostic and therapeutic implications for patients with PA.

An imputation-based genome-wide association study for growth and fatness traits in Sujiang pigs

Sujiang pigs are a synthetic breed derived from Jiangquhai, Fengjing, and Duroc pigs. In this study, we sequenced the genome of 62 pigs with a coverage depth of 10× to 20×, including 27 Sujiang and 35 founder breed pigs, and we collected 360 global pigs' genome sequence data from public databases including 39 Duroc pigs. We obtained a high-quality variant dataset of 365 Sujiang pigs by imputing the porcine 80 K single nucleotide polymorphism (SNP) Beadchip to the whole-genome scale with a total of 422 pigs as a reference panel. A dataset of 365 imputated Sujiang pigs was used to perform single-trait genome-wide association study (GWAS) and meta-analyses for growth and fatness traits. Single-trait GWAS identified 1 907, 18, and 14 SNPs surpassing the suggestively significant threshold for backfat thickness, chest circumference, and chest width, respectively. Meta-analyses identified 2 400 genome-wide significant SNPs and 520 suggestively significant SNPs for backfat thickness and chest circumference, and 719 genome-wide significant SNPs and 1 225 suggestively significant SNPs for all seven traits. According to the meta-analysis of backfat thickness and chest circumference, a remarkable region of 2.69 Mb on Sus scrofa chromosome 4 containing FAM110B, IMPAD1, LYN, MOS, PENK, PLAG1, SDR16C5 and XKR4 was identified as a candidate region. The haplotype heat map of the 2.69 Mb region verified that Sujiang pigs were derived from Duroc and Chinese indigenous pigs, especially Jiangquhai pigs. The Kruskal-Wallis test showed that haplotypes of the 2.69 Mb region significantly affected backfat thickness and chest circumference traits. We then focused on PLAG1, an important growth-related gene, and identified two synonymous SNPs with obvious differences among different breeds in the PLAG1 gene. We then performed genotyping of 365 Sujiang, 150 Duroc, 95 Jiangquhai, and 100 Fengjing pigs to confirm the above result and verified that the two variants significantly affected phenotypes of growth and fatness traits. Our findings not only provide insights into the genetic architecture of porcine growth and fatness traits but also provide potential markers for selective breeding of these traits in Sujiang pigs.

Pediatric fibromyxoid tumor with PLAG1 fusion: An emerging entity with a novel intracranial location

Translocations involving PLAG1 occur in several tumors, most commonly pleomorphic adenoma and lipoblastoma. Recently, a distinctive soft tissue tumor with a PLAG1 fusion has been reported in the pediatric age group. These are low grade tumors with a fibroblastic or mixed fibroblastic and myxoid morphology but no other lines of differentiation. They are typically immunopositive for desmin and CD34. The partner genes for these tumors have included YWHAZ, EEF1A1, ZFHX4l, CHCHD7, and PCMTD1. We report another case of this fibromyxoid tumor with a PLAG1 fusion, this time with COL3A1 as the partner gene. The fusion placed expression of a full-length PLAG1 protein under the control of the constitutively active COL3A1 promoter. Overexpression of PLAG1 was confirmed by diffusely positive immunostaining for PLAG1. The most novel aspect of this tumor is the intracranial location. Opinion has been divided over whether these tumors are a specific entity, or related to lipoblastoma, since that tumor also typically occurs in soft tissue in the pediatric age group and shows many of the same gene fusions. However, lipoblastoma has never been reported in an intracranial location and, thus, our case provides compelling evidence that this fibromyxoid tumor is indeed a distinct entity.

Microdeletions in 1q21 and 8q12.1 depict two additional molecular subgroups of Silver-Russell syndrome like phenotypes

Background

Silver-Russell syndrome (SRS) is a genetic disorder characterized by intrauterine and postnatal growth restriction, relative macrocephaly at birth, body asymmetry and typical facial features. Clinical and molecular heterogeneity is described in SRS. Common causes are loss of methylation of the imprinting center 1 in 11p15 and maternal uniparental disomy of chromosome 7. Other genetic alterations include disturbances of imprinted regions in 14q32, 7q32 and 11p15 as well as submicroscopic deletions and duplications. Single nucleotide variants in genes like IGF2, HMGA2, PLAG1, CDKN1C have also been identified in patients with SRS phenotypes. However, routine molecular diagnostics usually focus on 11p15 and chromosome 7, while less frequent causes are not systematically addressed.

Results

Here we report two patients with SRS features in which molecular karyotyping revealed microdeletions in 1q21 and 8q12.1 respectively. In a 3.5-year-old girl with postnatal growth restriction, feeding difficulties, relative macrocephaly and distinct SRS features a 2 Mb deletion in 1q21.1q21.2 was identified. Our second case is a 1.5-year-old boy with intrauterine and postnatal growth restriction, feeding difficulties and distinct facial features with a 77 kb deletion in 8q12.1 affecting PLAG1 as the only protein-encoding gene with known function.

Conclusions

The 1q21 region has not yet been assigned as an SRS region, although six patients with the same deletion and SRS features including relative macrocephaly have been described before. This new case adds to the evidence that distal 1q21 should be annotated as an SRS candidate region. The PLAGL1 alteration is the smallest deletion in 8q12.1 ever reported in a patient with SRS phenotype and it finally confirms that PLAG1 is the SRS causing gene in 8q12.1. To increase the diagnostic yield in patients with suspected SRS, we recommend both molecular karyotyping and next generation sequencing-based approaches.

PLAG1 Immunohistochemical Staining Is a Surrogate Marker for PLAG1 Fusions in Lipoblastomas

BACKGROUND

The hallmark of lipoblastoma is a PLAG1 fusion. PLAG1 protein overexpression has been reported in sporadic PLAG1-rearranged lipoblastomas.

METHODS

We evaluated the utility of PLAG1 immunohistochemical staining (IHC) in 34 pediatric lipomatous tumors, correlating the results with histology and conventional cytogenetics, FISH and/or next generation sequencing (NGS) results.

RESULTS

The study included 24 lipoblastomas, divided into 2 groups designated as "Lipoblastoma 1" with both lipoblastoma histology and PLAG1 rearrangement (n = 16) and "Lipoblastoma 2" with lipoblastoma histology but without PLAG1 cytogenetic rearrangement (n = 8), and 10 lipomas with neither lipoblastoma histology nor a PLAG1 rearrangement. Using the presence of a fusion as the "gold standard" for diagnosing lipoblastoma (Lipoblastoma 1), the sensitivity of PLAG1 IHC was 94%. Using histologic features alone (Lipoblastoma 1 + 2), the sensitivity was 96%. Specificity, as defined by the ability to distinguish lipoma from lipoblastoma, was 100%, as there were no false positives in the lipoma group.

CONCLUSIONS

Cytogenetics/molecular testing is expensive and may not be ideal for detecting PLAG1 fusions because PLAG1 fusions are often cytogenetically cryptic and NGS panels may not include all partner genes. PLAG1 IHC is an inexpensive surrogate marker of PLAG1 fusions and may be useful in distinguishing lipoblastomas from lipomas.

Long non-coding RNA MEG8 induced by PLAG1 promotes clear cell renal cell carcinoma through the miR-495-3p/G3BP1 axis

Clear cell renal cell carcinoma (ccRCC) is recognized as one of the most lethal malignancies among the urological system, with constantly increasing mortality. While the molecular mechanisms underlying ccRCC progression are still poorly understood, the molecular and functional role of lncRNA in multiple diseases has been well demonstrated. In this study, we hypothesized that lncRNA MEG8 might participate in ccRCC development. At first, we found that MEG8 expression was increased in ccRCC tumor tissues and cells. Next, we demonstrated that MEG8 knockdown suppressed cell viability, migration, and invasion in vitro and inhibited tumor growth in vivo. Subsequently, we utilized bioinformatics analysis, ChIP, and luciferase assays, and we found that PLAG1 could transcriptionally regulate MEG8 in ccRCC cells. Furthermore, MEG8 promoted G3BP1 expression to aggravate ccRCC tumorigenic properties through sponging miR-495-3p. Our study identified a novel PLAG1/MEG8/miR-495-3p/G3BP1 network in ccRCC development, which might be a promising direction for developing new diagnoses or therapeutic agents for ccRCC.

Integrative analysis of long non-coding RNAs and mRNAs associated with tumorigenesis of salivary gland pleomorphic adenoma

OBJECTIVE

The current study investigated long non-coding RNA (lncRNA) and mRNA profiles of the human salivary gland pleomorphic adenoma (SGPA).

DESIGN

Microarray analysis was used to study the expression of lncRNAs and mRNAs and the differentially expressed lncRNAs in human SGPA (all from parotid gland) were identified. The differentially expressed lncRNAs were subjected to qRT-PCR to verify and quantify their expression and a lncRNA-mRNA co-expression network was constructed. The lncRNAs correlated to pleomorphic adenoma gene 1 (PLAG1), a known key transcription factor, were identified and analyzed.

RESULTS

In the present study, 17,382 lncRNAs and 8132 mRNAs were found to be significantly differentially expressed in SGPA (fold change > 2, P < 0.05). The expression of three lncRNAs (NR_110874, NR_110875 and T087085) was significantly altered in SGPA compared to the corresponding healthy tissues, and it was confirmed using the lncRNA-mRNA co-expression network analysis that several lncRNAs interact with 5 key regulators (PLAG1, CTNNB1, CCND1, IGF2, and TP53). Furthermore, T042819 was significantly upregulated in SGPA, which may upregulate PLAG1 by sponging has-miR195-5p.

CONCLUSION

These data suggested that the differently expressed lncRNAs may contribute to the tumorigenesis of SGPA, and analyzing the differences in the lncRNA expression profiles may provide novel insights into the pathogenesis of SGPA.

FTO and PLAG1 Genes Expression and FTO Methylation Predict Changes in Circulating Levels of Adipokines and Gastrointestinal Peptides in Children

Adipokines and gastrointestinal tract hormones are important metabolic parameters, and both epigenetic factors and differential gene expression patterns may be associated with the alterations in their concentrations in children. The function of the FTO gene (FTO alpha-ketoglutarate dependent dioxygenase) in the regulation of the global metabolic rate is well described, whereas the influence of protooncogene PLAG1 (PLAG1 zinc finger) is still not fully understood. A cross-sectional study on a group of 26 children with various BMI values (15.3–41.7; median 28) was carried out. The aim was to evaluate the dependencies between the level of methylation and expression of aforementioned genes with the concentration of selected gastrointestinal tract hormones and adipokines in children. Expression and methylation were measured in peripheral blood mononuclear DNA by a microarray technique and a restriction enzyme method, respectively. All peptide concentrations were determined using the enzyme immunoassay method. The expression level of both FTO and PLAG1 genes was statistically significantly related to the concentration of adipokines: negatively for apelin and leptin receptor, and positively for leptin. Furthermore, both FTO methylation and expression negatively correlated with the concentration of resistin and visfatin. Cholecystokinin was negatively correlated, whereas fibroblast growth factor 21 positively correlated with methylation and expression of the FTO gene, while FTO and PLAG1 expression was negatively associated with the level of cholecystokinin and glucagon-like peptide-1. The PLAG1 gene expression predicts an increase in leptin and decrease in ghrelin levels. Our results indicate that the FTO gene correlates with the concentration of hormones produced by the adipose tissue and gastrointestinal tract, and PLAG1 gene may be involved in adiposity pathogenesis. However, the exact molecular mechanisms still need to be clarified.

Diagnosis and management of oral cavity lipoblastoma and lipoblastomatosis in an 8-month-old boy

Lipoblastoma/lipoblastomatosis presents some unique diagnostic and therapeutic challenges when encountered in the oral cavity. In these rare cases, diagnostic confirmation with molecular testing and a conservative surgical resection can contribute to successful management.

The histological and molecular spectrum of lipoblastoma: A case series with identification of three novel gene fusions by targeted RNA-sequencing

Lipoblastoma is a rare benign mesenchymal neoplasm that typically occurs in infancy but may also occur in older age groups and various locations. Thus, there are often numerous clinical differential diagnoses. Moreover, lipoblastomas can show a broad histologic spectrum, which can hamper the correct diagnosis, particularly in small biopsies. At the genomic level, lipoblastomas are characterized by chromosomal fusions involving the PLAG1 gene. We investigated 11 lipoblastoma samples from 10 pediatric patients (age range five months to 12 years), including one patient with local recurrence, in view of their histopathological features, and performed targeted RNA sequencing. We found a broad histological spectrum with some tumors with prominent myxoid changes, but also tumors composed mainly of mature adipocytic cells, and classified the cases according to the literature as classic (mixed), maturing, or myxoid subtype. By targeted RNA sequencing analysis, we identified characteristic PLAG1 rearrangements in 70% of the investigated cases. Moreover, these analyses revealed three novel gene fusions, two affecting the PLAG1 gene and one involving HMGA2. Besides, we performed PLAG1 immunohistochemistry and identified positive cells, typically immature adipocytic cells and spindle cells, at various numbers in all cases. However, in the maturing areas, only very sparsely positive cells were found, limiting the value of the PLAG1 immunohistochemistry as an adjunct in the diagnosis of lipoblastoma, particularly for the maturing subtype and small biopsies. The presented case series confirms the broad morphological spectrum of lipoblastoma described in the literature and underlines the value of modern molecular diagnostic approaches as a supportive diagnostic tool in challenging cases and for gaining further insights into the molecular basis of this rare mesenchymal tumor.

PLAG1-rearrangment in a uterine leiomyosarcoma with myxoid stroma and heterologous differentiation

A variety of molecular alterations have been reported in uterine leiomyosarcomas, but most are considered nondiagnostic. There are, however, rare exceptions including PLAG1 rearrangement which has recently been identified in a subset of myxoid leiomyosarcomas. A 41-year-old woman presented with symptoms of a fibroid. She underwent a myomectomy which revealed a high-grade uterine sarcoma with areas of myxoid stroma and heterologous elements. The tumor expressed desmin, smooth muscle actin, H-caldesmon, and estrogen and progesterone receptors. RNA sequencing revealed a novel TRIM13-PLAG1 fusion gene which was subsequently independently confirmed by fluorescence in situ hybridization. On further evaluation the patient was found to have multiple pulmonary metastases and died due to disease progression shortly after diagnosis. This report describes a novel fusion partner of PLAG1 in a uterine leiomyosarcoma with myxoid leiomyosarcoma and heterologous elements, thereby broadening the spectrum of morphologic and genetic findings within this rare group of neoplasms.

Further heterogeneity in Silver-Russell syndrome: PLAG1 deletion in association with a complex chromosomal rearrangement

Silver-Russell syndrome (SRS) is a rare genetic condition primarily characterized by growth restriction and facial dysmorphisms. While hypomethylation of H19/IGF2:IG-DMR (imprinting control region 1 [IC1]) located at 11p15.5 and maternal uniparental disomy of chromosome 7 (upd[7]mat) are the most common genetic mechanisms responsible for SRS, the expanding body of literature describing alternative causative variants suggests SRS is a highly heterogeneous condition, also involving variation in the HMGA2-PLAG1-IGF2 pathway. We report a familial PLAG1 deletion in association with a complex chromosomal rearrangement. We describe two siblings with differing unbalanced chromosomal rearrangements inherited from a mother with a 5-breakpoint balanced complex rearrangement involving chromosomes 2, 8, and 21. The overlapping but diverse phenotypes in the siblings were characterized by shared SRS-like features, underlined by a PLAG1 whole gene deletion. Genetic analysis and interpretation was further complicated by a meiotic recombination event occurring in one of the siblings. This family adds to the limited literature available on PLAG1-related SRS. We have reviewed all currently known cases aiming to define the associated phenotype and guide future genetic testing strategies. The heterogeneity of SRS is further expanded by the involvement of complex cytogenomic abnormalities, imposing requirements for a comprehensive approach to testing and genetic counseling.

Methylation and Expression of FTO and PLAG1 Genes in Childhood Obesity: Insight into Anthropometric Parameters and Glucose-Lipid Metabolism

The occurrence of childhood obesity is influenced by both genetic and epigenetic factors. FTO (FTO alpha-ketoglutarate dependent dioxygenase) is a gene of well-established connection with adiposity, while a protooncogene PLAG1 (PLAG1 zinc finger) has been only recently linked to this condition. We performed a cross-sectional study on a cohort of 16 obese (aged 6.6-17.7) and 10 healthy (aged 11.4-16.9) children. The aim was to evaluate the relationship between methylation and expression of the aforementioned genes and the presence of obesity as well as alterations in anthropometric measurements (including waist circumference (WC), body fat (BF_kg) and body fat percent (BF_%)), metabolic parameters (lipid profile, blood glucose and insulin levels, presence of insulin resistance) and blood pressure. Expression and methylation were measured in peripheral blood mononuclear cells using a microarray technique and a method based on restriction enzymes, respectively. Multiple regression models were constructed to adjust for the possible influence of age and sex on the investigated associations. We showed significantly increased expression of the FTO gene in obese children and in patients with documented insulin resistance. Higher FTO expression was also associated with an increase in WC, BF_kg, and BF_% as well as higher fasting concentration of free fatty acids (FFA). FTO methylation correlated positively with WC and BF_kg. Increase in PLAG1 expression was associated with higher BF%. Our results indicate that the FTO gene is likely to play an important role in the development of childhood adiposity together with coexisting impairment of glucose-lipid metabolism.

Expression of PLAG1, HMGA1 and HMGA2 in minor salivary glands tumours

Background

Diagnosis of minor salivary gland (MSG) tumours is often difficult, due to the scarce tissue obtained from bioptic excision and complex histopathological differential diagnosis. In our study we performed an immunohistochemical analysis of PLAG1, HMGA1 and HMGA2 on a series of MSG tumours, in order to develop a new helpful diagnostic panel.

Methods

A retrospective series of 17 surgical specimens of MSG tumours were analysed for the expression of PLAG1, HMGA1 and HMGA2. Three control cases were enrolled and analysed. An intensity and percentage-based approach was performed, creating a combined score panel.

Results

PLAG1 facilitate the diagnosis of benign tumours, discriminating it from malignant histotypes, with a defined cut-off value. Similarly, HMGA1 is significantly higher in benign histotypes than in malignant ones. HMGA2 in our series, did not reveal any association in identifying benign from malignant histotypes.

Conclusions

In this study we assessed the diagnostic role of PLAG1, HMGA1 and HMGA2 immunohistochemical analysis. The score panel facilitate histopathological diagnosis of these rare tumours, helping to distinguish benign tumours from malignant ones and ameliorating the differential diagnosis of specific histotypes.

Novel morphologic findings in PLAG1-rearranged soft tissue tumors

Oncogenesis in PLAG1-rearranged tumors often results from PLAG1 transcription factor overexpression driven by promoter-swapping between constitutively expressed fusion partners. PLAG1-rearranged tumors demonstrate diverse morphologies. This study adds to this morphologic heterogeneity by introducing two tumors with PLAG1 rearrangements that display distinct histologic features. The first arose in the inguinal region of a 3-year-old, appeared well-circumscribed with a multinodular pattern, and harbored two fusions: ZFHX4-PLAG1 and CHCHD7-PLAG1. The second arose in the pelvic cavity of a 15-year-old girl, was extensively infiltrative and vascularized with an adipocytic component, and demonstrated a COL3A1-PLAG1 fusion. Both showed low-grade cytomorphology, scarce mitoses, no necrosis, and expression of CD34 and desmin. The ZFHX4-/CHCHD7-PLAG1-rearranged tumor showed no evidence of recurrence after 5 months. By contrast, the COL3A1-PLAG1-rearranged tumor quickly recurred following primary excision with positive margins; subsequent re-excision with adjuvant chemotherapy resulted in no evidence of recurrence after 2 years. While both tumors show overlap with benign and malignant fibroblastic and fibrovascular neoplasms, they also display divergent features. These cases highlight the importance of appropriate characterization in soft tissue tumors with unusual clinical and histologic characteristics.

Pleomorphic adenoma: the great mimicker of malignancy

Pleomorphic adenoma (PA) is the most common salivary gland neoplasm, and its diagnosis is straightforward in the majority of cases. However, not infrequently, PA shows unusual and uncommon histological features that can be confused with those of malignancy. The difficulties in diagnosing PA arise from its ability to mimic invasion, show atypical or metaplastic cytomorphology, and show morphological features that overlap with those of established salivary gland carcinomas. In addition, recognising early malignant transformation to carcinoma ex-pleomorphic adenoma continues to be a frequent challenge. This review describes the diagnostic pitfalls of PA, and offers a systematic approach to avoid them by combining classic histopathology with novel immunohistochemical and molecular tests.

Myoepithelial Carcinoma

Myoepithelial carcinoma (MECA) may overlap histologically with other salivary gland neoplasms, especially pleomorphic adenoma. MECA is characterized by cellular, uniform growth of myoepithelial cells and multinodular expansile invasive pattern with zonal cellular distribution. It may arise de novo or in association with pleomorphic adenoma (myoepithelial carcinoma ex pleomorphic adenoma). By immunohistochemistry, MECA is positive for cytokeratins and at least one of the myoepithelial markers, including S100. PLAG1 fusion is the most common genetic alteration. Carcinoma ex pleomorphic adenoma and necrosis correlate with worse clinical outcome in MECA, and necrosis can be used to stratify MECA as high grade.

Pediatric fibromyxoid soft tissue tumor with PLAG1 fusion: A novel entity?

The classification of undifferentiated soft tissue tumors continues to evolve with the expanded application of molecular analysis in clinical practice. We report three cases of a unique soft tissue tumor in young children (5 months to 2 years old) displaying a purely fibromyxoid histology, with positive staining for desmin and CD34. In two cases, RNA sequencing detected a YWHAZ-PLAG1 gene fusion, while in the third case, a previously unreported EEF1A1-PLAG1 fusion was identified. PLAG1 fusions have been reported in several pathologic entities including pleomorphic adenoma, myoepithelial tumors of skin and soft tissue, and lipoblastoma, the latter occurring preferentially in young children. In these tumors, expression of a full length PLAG1 protein comes under the control of the constitutively active promoter of the partner gene in the fusion, and the current cases conform to that model. Overexpression of PLAG1 was confirmed by diffusely positive immunostaining for PLAG1 in all three cases. Our findings raise the possibility of a novel fibromyxoid neoplasm in childhood associated with these rare PLAG1 fusion variants. The only other report of a PLAG1-YWHAZ fusion occurred in a pediatric tumor diagnosed as a "fibroblastic lipoblastoma." This finding raises the possibility of a relationship with our three cases, even though our cases lacked any fat component. Further studies with regard to a shared pathogenesis are required.

Recent advances in smooth muscle tumors with PGR and PLAG1 gene fusions and myofibroblastic uterine neoplasms

Uterine epithelioid and myxoid leiomyosarcomas and inflammatory myofibroblastic tumors are rare mesenchymal neoplasms. Next-generation sequencing recently detected novel PGR fusions in uterine epithelioid leiomyosarcomas that demonstrate characteristic rhabdoid and spindled morphology. PLAG1 gene fusions have also been identified in a subset of myxoid leiomyosarcomas and are associated with PLAG1 overexpression. ALK rearrangements underpin the vast majority of uterine inflammatory myofibroblastic tumors, which demonstrate morphologic, and immunohistochemical features similar to those of inflammatory myofibroblastic tumors elsewhere. This review summarizes the morphologic, immunophenotypic, and molecular genetic features of PGR fusion-positive epithelioid leiomyosarcoma, PLAG1 fusion-positive myxoid leiomyosarcoma, and inflammatory myofibroblastic tumors of the uterus.

Novel Variant in PLAG1 in a Familial Case with Silver-Russell Syndrome Suspicion

Silver-Russell syndrome (SRS) is a rare growth-related genetic disorder that is mainly associated with prenatal and postnatal growth retardation. Molecular causes are not clear in all cases, the most common ones being loss of methylation on chromosome 11p15 (≈50%) and maternal uniparental disomy for chromosome 7 (upd(7)mat) (≈10%). However, pathogenic variants in genes such as CDKN1C, HMGA2, IGF2, or PLAG1 have also been described. Previously, two families and one sporadic case have been reported with PLAG1 alterations. Here, we present a case of a female with clinical suspicion of SRS (i.e., intrauterine and postnatal growth retardation, triangular face, psychomotor delay, speech delay, feeding difficulties). No alterations in methylation or copy number were detected at chromosomes 11p15 and 7 using methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA). The custom panel study by next-generation sequencing (NGS) revealed a frameshift variant in the PLAG1 gene (NM_002655.3:c.551delA; p.(Lys184Serfs *45)). Familial studies confirmed that the variant was inherited from the mother and it was also present in other family members. New evidence of pathogenic alterations in the HMGA2-PLAG1-IGF2 pathway suggest the importance of studying and taking into account these genes as alternative molecular causes of Silver-Russell syndrome.

NDRG1-PLAG1 and TRPS1-PLAG1 Fusion Genes in Chondroid Syringoma

BACKGROUND/AIM

Chondroid syringoma is a rare benign tumor emanating from sweat glands. Although rearrangements of the pleomorphic adenoma gene 1 (PLAG1) have been reported in such tumors, information on PLAG1 fusion genes is very limited.

MATERIALS AND METHODS

Cytogenetic, fluorescence in situ hybridization, RNA sequencing, array comparative genomic hybridization, reverse transcription polymerase chain reaction, and Sanger sequencing analyses were performed on two chondroid syringoma cases.

RESULTS

Both tumors had structural rearrangements of chromosome 8. An NDRG1-PLAG1 transcript was found in the first tumor in which exon 3 of PLAG1 was fused with exon 1 of NDRG1. A TRPS1-PLAG1 chimeric transcript was detected in the second chondroid syringoma in which exon 2 or exon 3 of PLAG1 was fused with exon 1 of TRPS1.

CONCLUSION

The NDRG1-PLAG1 and TRPS1-PLAG1 resemble other PLAG1 fusion genes inasmuch as the expression of PLAG1 comes under the control of the NDRG1 or TRPS1 promoter.

Myoepithelioma of soft tissue and bone, and myoepithelioma-like tumors of the vulvar region: Clinicopathological study of 15 cases by PLAG1 immunohistochemistry

We demonstrated the clinicopathological findings of 13 myoepitheliomas of soft tissue and bone (MESTBs) and two myoepithelioma-like tumors of the vulvar region (MELTVRs), focusing on the association between nuclear atypia and clinical course, and the utility of immunohistochemistry (IHC) of pleomorphic adenoma gene 1 (PLAG1) for the pathological diagnosis of these tumors. Of the 13 MESTBs, eight, one and four cases exhibited mild, moderate and severe nuclear atypia, respectively. Two cases with venous invasion showed severe nuclear atypia and both died of advanced disease. Two MELTVR cases showed moderate nuclear atypia and had no evidence of disease after surgery. On IHC, 12 of 13 (92.3%) MESTBs showed PLAG1 immunoreactivity and none of the MELTVRs expressed PLAG1. In addition, MELTVRs showed loss of INI1 expression. In contrast, all MESTBs retained INI1 expression. Fluorescence in situ hybridization detected EWSR1, FUS and PLAG1 rearrangement in 5 (38.5%), 0 (0%) and 2 (15.4%) of the 13 MESTBs, respectively. No EWSR1, FUS and PLAG1 rearrangement were observed in the METLVRs. In conclusion, MESTBs with both severe nuclear atypia and venous invasion would be indicative of malignant potential. PLAG1 might be a useful IHC marker in MESTB diagnosis.

Activation of PLAG1 and HMGA2 by gene fusions involving the transcriptional regulator gene NFIB

The pleomorphic adenoma (PA), which is the most common salivary gland neoplasm, is a benign tumor characterized by recurrent chromosome rearrangements involving 8q12 and 12q14-15. We have previously shown that the PLAG1 and HMGA2 oncogenes are the targets of these rearrangements. Here, we have identified previously unrecognized subsets of PAs with ins(9;8)/t(8;9) (n = 5) and ins(9;12)/t(9;12) (n = 8) and breakpoints located in the vicinity of the PLAG1 and HMGA2 loci. RNA-sequencing and reverse transcriptase (RT)-PCR analyses of a case with an ins(9;8) revealed a novel NFIB-PLAG1 fusion in which NFIB exon 4 is linked to PLAG1 exon 3. In contrast to the developmentally regulated PLAG1 gene, NFIB was highly expressed in normal salivary gland, indicating that PLAG1 in this case, as in other variant fusions, is activated by promoter swapping. RT-PCR analysis of three PAs with t(9;12) revealed two tumors with chimeric transcripts consisting of HMGA2 exon 4 linked to NFIB exons 9 or 3 and one case with a fusion linking HMGA2 exon 3 to NFIB exon 9. The NFIB fusion events resulted in potent activation of PLAG1 and HMGA2. Analysis of the chromatin landscape surrounding NFIB revealed several super-enhancers in the 5'- and 3'-parts of the NFIB locus and its flanking sequences. These findings indicate that PLAG1 and HMGA2, similar to MYB in adenoid cystic carcinoma, may be activated by enhancer-hijacking events, in which super-enhancers in NFIB are translocated upstream of PLAG1 or downstream of HMGA2. Our results further emphasize the role of NFIB as a fusion partner to multiple oncogenes in histopathologically different types of salivary gland tumors.

New molecular insights into the pathogenesis of lipoblastomas: clinicopathologic, immunohistochemical, and molecular analysis in pediatric cases

Lipoblastomas can occasionally require further molecular confirmation when occurring outside of the usual age groups or demonstrating unusual morphology. We reviewed 28 lipoblastomas with 16 controls. Lipoblastomas were subdivided into myxoid (n = 7), classic (n = 9), or lipoma-like (n = 12) subtypes. PLAG1 immunohistochemistry, PLAG1 fluorescence in situ hybridization (FISH), and targeted RNA sequencing were performed on formalin-fixed paraffin-embedded tissue. Karyotypes were available in a subset of lipoblastomas (n = 9). Gene rearrangements were identified in 17/25 (68%) lipoblastomas, including PLAG1 (15/25, 60%) and HMGA2 (2/25, 8%). Five novel fusion partners (DDX6, KLF10, and KANSL1L with PLAG1 and EP400 and FGD6 with HMGA2) were found. PLAG1 immunohistochemistry was positive (nuclear, moderate/strong) in myxoid and classic subtypes lipoblastomas with preferential expression in mesenchymal cells within myxoid stroma and fibrous septa and negative in all controls. When comparing PLAG1 immunohistochemistry with molecular testing (FISH and/or RNA sequencing and/or karyotype), concordant results were noted in 13/25 (52%) cases, increasing to 15/25 (60%) after slight adjustment of the PLAG1 FISH positive threshold. In myxoid and classic lipoblastomas, PLAG1 immunohistochemistry seems to be a better surrogate marker for PLAG1 rearrangement, as compared with lipoma-like subtypes. In lipoma-like subtypes, targeted RNA sequencing appears to detect PLAG1 fusions better than FISH and immunohistochemistry. The preferential expression of PLAG1 in the mesenchymal and fibroblast-like cells deserves further investigation as the putative cell of origin in lipoblastoma.

What is hiding behind S100 protein and SOX10 positive oncocytomas? Oncocytic pleomorphic adenoma and myoepithelioma with novel gene fusions in a subset of cases

Oncocytomas (OCs) in salivary glands are rare benign tumors composed of mitochondria-rich epithelial cells (oncocytes), mostly localized in the parotid gland. The treatment of choice is simple excision. Extensive oncocytic metaplasia of pleomorphic adenoma (PA) and myoepithelioma (ME) can be diagnostically challenging and may camouflage the correct diagnosis. These tumors should be treated more carefully compared with OC, given the risk of frequent recurrences and the possibility of malignant transformation. We have investigated 89 oncocytic lesions from our files, including OC (n = 74) and metaplastic oncocytic variant of PA/ME (n = 15). All OCs were stained for S100 protein and SOX10. The tumors with immunohistochemical expression of one or both markers were tested by next-generation sequencing (NGS). The NGS results were confirmed by reverse transcription-polymerase chain reaction (RT-PCR) and/or fluorescence in situ hybridization (FISH). Ten cases originally diagnosed as OC, and 1 low-grade uncertain oncocytic tumor (11/74) revealed nuclear-cytoplasmic and/or nuclear positivity for S100 protein and/or SOX10, respectively. Fusion transcripts CHCHD7-PLAG1 and GEM-PLAG1 were found in 2 cases (1 fusion in each), and these were confirmed by RT-PCR and PLAG1 break-apart FISH probe, respectively. Another 5 cases were positive for PLAG1 rearrangement by FISH. In the control group of 15 oncocytic PA/ME, 4/15 tested tumors harbored gene fusions including NFT3-PLAG1, CHCHD7-PLAG1, FBXO32-PLAG1, and C1orf116-PLAG1 (1 fusion in each case) as detected by NGS. Two fusions were confirmed by RT-PCR, 1 case by FISH, and 1 case was not analyzable by FISH. We additionally tested 24 OCs negative for S100 protein and SOX10 by immunohistochemistry (IHC) and by FISH for rearrangement of PLAG1 gene, but none of them were positive. SOX10 and/or S100 protein immunopositivity in conjunction with rearrangement of the PLAG1 gene assisted in reclassification of a subset of oncocytomas as oncocytic variants of PA and ME. Therefore, we recommend to include S100 protein and SOX10 IHC when diagnosing tumors with predominantly oncocytoma-like differentiation. In addition, by NGS, 3 new gene fusions were detected in oncocytic ME, including NTF3-PLAG1, FBXO32-PLAG1, and GEM-PLAG1, and a new fusion C1orf116-PLAG1 was detected in oncocytic PA.

Contribution of gene mutations to Silver-Russell syndrome phenotype: multigene sequencing analysis in 92 etiology-unknown patients

BACKGROUND

Silver-Russell syndrome (SRS) is characterized by growth failure and dysmorphic features. Major (epi)genetic causes of SRS are loss of methylation on chromosome 11p15 (11p15 LOM) and maternal uniparental disomy of chromosome 7 (upd(7)mat). However, IGF2, CDKN1C, HMGA2, and PLAG1 mutations infrequently cause SRS. In addition, other imprinting disturbances, pathogenic copy number variations (PCNVs), and monogenic disorders sometimes lead to SRS phenotype. This study aimed to clarify the frequency and clinical features of the patients with gene mutations among etiology-unknown patients with SRS phenotype.

RESULTS

Multigene sequencing was performed in 92 out of 336 patients referred to us for genetic testing for SRS. The clinical features of the patients were evaluated based on the Netchine-Harbison clinical scoring system. None of the patients showed 11p15 LOM, upd(7)mat, abnormal methylation levels for six differentially methylated regions (DMRs), namely, PLAGL1:alt-TSS-DMR on chromosome 6, KCNQ1OT1:TSS-DMR on chromosome 11, MEG3/DLK1:IG-DMR on chromosome 14, MEG3:TSS-DMR on chromosome 14, SNURF:TSS-DMR on chromosome 15, and GNAS A/B:TSS-DMR on chromosome 20, PCNVs, or maternal uniparental disomy of chromosome 16. Using next-generation sequencing and Sanger sequencing, we screened four SRS-causative genes and 406 genes related to growth failure and/or skeletal dysplasia. We identified four pathogenic or likely pathogenic variants in responsible genes for SRS (4.3%: IGF2 in two patients, CDKN1C, and PLAG1), and five pathogenic variants in causative genes for known genetic syndromes presenting with growth failure (5.4%: IGF1R abnormality (IGF1R), SHORT syndrome (PIK3R1), Floating-Harbor syndrome (SRCAP), Pitt-Hopkins syndrome (TCF4), and Noonan syndrome (PTPN11)). Functional analysis indicated the pathogenicity of the CDKN1C variant. The variants we detected in CDKN1C and PLAG1 were the second and third variants leading to SRS, respectively. Our patients with CDKN1C and PLAG1 variants showed similar phenotypes to previously reported patients. Furthermore, our data confirmed IGF1R abnormality, SHORT syndrome, and Floating-Harbor syndrome are differential diagnoses of SRS because of the shared phenotypes among these syndromes and SRS. On the other hand, the patients with pathogenic variants in causative genes for Pitt-Hopkins syndrome and Noonan syndrome were atypical of these syndromes and showed partial clinical features of SRS.

CONCLUSIONS

We identified nine patients (9.8%) with pathogenic or likely pathogenic variants out of 92 etiology-unknown patients with SRS phenotype. This study expands the molecular spectrum of SRS phenotype.

Identification of CTNNB1-PLAG1 gene rearrangement in a patient with pulmonary pleomorphic adenoma

Pulmonary pleomorphic adenoma (PA) is a rare salivary gland-type neoplasm, which predominantly occurs in the proximal airway. Rearrangement of the pleomorphic adenoma gene 1 (PLAG1) is the most frequent genetic event in PAs of salivary glands. However, whether pulmonary PA also harbors PLAG1 rearrangement has not been elucidated. Here, we present a case of pulmonary PA, located at the middle lobar bronchus, in a 54-year-old man. CTNNB1-PLAG1 gene fusion was identified by reverse transcription-polymerase chain reaction using formalin-fixed paraffin-embedded tissue (FFPE). Furthermore, immunohistochemical analysis revealed nuclear expression of PLAG1 in all tumor cells. To the best of our knowledge, this is the first reported case of pulmonary PA with CTNNB1-PLAG1 fusion and PLAG1 expression. Our case illustrates the possibility that pulmonary PA could be underpinned by recurrent PLAG1 translocations akin to salivary gland PA.

Soft Tissue Special Issue: Myoepithelial Neoplasms of Soft Tissue: An Updated Review with Emphasis on Diagnostic Considerations in the Head and Neck

Primary myoepithelial neoplasms of soft tissue have been shown to be related to their salivary gland counterparts, with which they often share morphologic, immunophenotypic, and molecular genetic features, such as the presence of PLAG1 rearrangement in both soft tissue mixed tumor and salivary pleomorphic adenoma. However, important distinctions remain between soft tissue and salivary myoepithelial neoplasms, namely differing criteria for malignancy. This review provides an overview of the current understanding of the clinicopathologic and molecular features of soft tissue myoepithelial neoplasms, including discussion of the similarities and differences between soft tissue and salivary counterparts and relevant diagnostic issues specific to head and neck pathology practice.

Tubular apocrine adenoma of the eyelid - A case report and literature review

Tubular apocrine adenoma is a rare benign adnexal neoplasm most commonly identified in the scalp, composed of a dermal proliferation of apocrine tubules in a background of hyalinized stroma. Tubular apocrine adenoma can be a component of various sweat gland tumors and can also morphologically overlap with other sweat gland neoplasms. Isolated tubular apocrine adenoma arising in the glands of Moll is exceedingly rare, with only 4 previously reported cases. We present a 63-year-old male with tubular apocrine adenoma of the left upper eyelid, which recurred following initial incomplete excision. Although the lesion showed focal morphologic similarity to the apocrine variant of pleomorphic adenoma (chondroid syringoma), the diagnosis of tubular apocrine adenoma was supported by fluorescence in situ hybridization studies, which demonstrated absence of PLAG1 and HMGA2 gene rearrangements seen in pleomorphic adenoma. This case illustrates the clinical, microscopic and immunohistochemical features of tubular apocrine adenoma. The recent advances in our understanding of the molecular genetics of tubular apocrine adenoma and related tumors, and how these advances shape the evolving classification of sweat gland tumors are reviewed.

PLAG1 and USF2 Co-regulate Expression of Musashi-2 in Human Hematopoietic Stem and Progenitor Cells

MSI2, which is expressed predominantly in hematopoietic stem and progenitor cells (HSPCs), enforces HSPC expansion when overexpressed and is upregulated in myeloid leukemias, indicating its regulated transcription is critical to balanced self-renewal and leukemia restraint. Despite this, little is understood of the factors that enforce appropriate physiological levels of MSI2 in the blood system. Here, we define a promoter region that reports on endogenous expression of MSI2 and identify USF2 and PLAG1 as transcription factors whose promoter binding drives reporter activity. We show that these factors co-regulate, and are required for, efficient transactivation of endogenous MSI2. Coincident overexpression of USF2 and PLAG1 in primitive cord blood cells enhanced MSI2 transcription and yielded cellular phenotypes, including expansion of CD34+ cells in vitro, consistent with that achieved by direct MSI2 overexpression. Global chromatin immunoprecipitation sequencing analyses confirm a preferential co-binding of PLAG1 and USF2 at the promoter of MSI2, as well as regulatory regions corresponding to genes with roles in HSPC homeostasis. PLAG1 and USF2 cooperation is thus an important contributor to stem cell-specific expression of MSI2 and HSPC-specific transcriptional circuitry.

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We define a regulatory region governing physiological MSI2 expression in human HSPCs

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USF2 and PLAG1 collaboratively control endogenous HSPC-specific MSI2 expression

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MSI2 expression and stemness is maintained in culture upon USF2 and PLAG1 co-overexpression

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USF2 and PLAG1 exhibit genomic co-localization and associate with autophagy genes

PLAG1 expression and target genes in the hypothalamo-pituitary system in male mice

Knockout of pleomorphic adenoma gene 1 (PLAG1) in mice results in reduced fertility. To investigate whether PLAG1 is involved in reproductive control by the hypothalamo-pituitary system in males, we determined PLAG1 expression sites and compared gene expression between hypothalami and pituitary glands from Plag1 knockout and wildtype animals. Abundant expression of PLAG1 was detected throughout the pituitary gland, including gonadotropes and somatotropes. The hypothalamus also contained a large number of PLAG1-expressing cells. PLAG1 was expressed in some gonadotropin-releasing hormone neurons, but not in kisspeptin neurons. Gene ontology analysis indicated upregulation of cell proliferation in both structures, and of cholesterol biosynthesis in the hypothalamus, but functional confirmation is required. Expression levels of pituitary gonadotropins and gonadotropin-releasing hormone receptor, and of brain gonadotropin-releasing hormone and kisspeptin mRNA were unaffected in knockout mice. We conclude that PLAG1 deficiency does not have a major impact on the reproductive control by the hypothalamo-pituitary system.

Association of Copy Number Variation at Intron 3 of HMGA2 With Navel Length in Bos indicus

Navel injuries caused by friction against the pasture can promote infection, reproductive problems and costly treatments in beef cattle raised in extensive systems. A haplotype-based genome-wide association study (GWAS) was performed for visual scores of navel length at yearling in Nellore cattle (Bos indicus) using data from 2,016 animals and 503,088 single nucleotide polymorphism (SNP) markers. The strongest signal (p = 1.01 × 10^-9) was found on chromosome 5 spanning positions 47.9-48.2 Mbp. This region contains introns 3 and 4 and exons 4 and 5 of the high mobility group AT-hook 2 gene (HMGA2). Further inspection of the region with whole genome sequence data of 21 Nellore bulls revealed correlations between counts of the significant haplotype and copy number gains of a ∼6.2 kbp segment of intron 3 of HMGA2. Analysis of genome sequences from five African B. indicus and four European Bos taurus breeds revealed that the copy number variant (CNV) is indicine-specific. This intronic CNV was then validated through quantitative polymerase chain reaction (qPCR) using Angus animals as copy neutral controls. Importantly, the CNV was not detectable by means of conventional SNP-based GWAS or SNP probe intensity analyses. Given that HMGA2 affects the expression of the insulin-like growth factor 2 gene (IGF2) together with the pleomorphic adenoma gene 1 (PLAG1), and that the latter has been repeatedly shown to be associated with quantitative traits of economic importance in cattle, these findings highlight the emerging role of variants impacting the insulin-like growth factor pathway to cattle breeding.

Clinicopathological effect of PLAG1 fusion genes in pleomorphic adenoma and carcinoma ex pleomorphic adenoma with special emphasis on histological features

AIMS

Pleomorphic adenoma gene 1 (PLAG1) rearrangement is well known in pleomorphic adenoma (PA), which is histologically characterised by admixed epithelial and mesenchymal components. Multiple fusion variants of PLAG1 and HMGA2 have been reported; currently, however, little is known regarding the clinicopathological impacts of these fusion types METHODS AND RESULTS: We examined the PLAG1- and HMGA2-related fusion status in 105 PAs and 11 cases of carcinoma ex PAs (CXPA) arising from salivary glands and lacrimal glands to elucidate their correlation to the clinicopathological factors. Forty cases harboured PLAG1 fusion genes: CTNNB1-PLAG1 in 22 cases, CHCHD7-PLAG1 in 14 cases and LIFR-PLAG1 in four cases. Only two cases possessed HMGA2 fusion genes. The mean age of LIFR-PLAG1-positive cases was significantly higher than that of CTNNB1-PLAG1- and CHCHD7-PLAG1-positive cases (P = 0.0358). PAs located in the submandibular gland demonstrated CTNNB1-PLAG1 fusion at a significantly higher rate than other fusions (P = 0.0109). Histologically, PLAG1 fusion-positive cases exhibited chondroid formation and plasmacytoid features more commonly (P = 0.043, P = 0.015, respectively) and myxoid abundant feature less frequently (P = 0.031) than PLAG1 fusion-negative cases. For CXPAs, four CTNNB1-PLAG1 fusions were detected in two salivary duct carcinomas and two myoepithelial carcinomas. Ductal formation was observed frequently (90.9%) in residual PA.

CONCLUSIONS

The presence of PLAG1 fusion was associated with specific histological features in PA. Detecting the PLAG1 fusion gene and searching residual ductal formation in salivary gland malignant tumours with extensive hyalinisation could be useful for diagnosis.

Expression of PTEN, Androgen Receptor, HER2/neu, Cytokeratin 5/6, Estrogen Receptor-Beta, HMGA2, and PLAG1 in Salivary Duct Carcinoma

Salivary duct carcinoma (SDC) is an aggressive neoplasm that resembles high-grade invasive ductal carcinoma of the breast. It can develop de novo or from the malignant transformation of pleomorphic adenoma (PA). We performed immunohistochemical stains for phosphatase and tensin homologue [PTEN androgen receptor (AR)], HER2/neu, cytokeratin 5/6, estrogen receptor-beta, high-mobility group AT-hook 2 (HMGA2), and pleomorphic adenoma gene 1 (PLAG1) on tissue microarray samples of 75 SDCs and 31 adenocarcinomas, not otherwise specified (NOS). Our data showed the following in SDC samples: loss of PTEN was found in 17 of 60 (28.3%); AR was expressed in 43 of 62 (69.4%); HER2/neu was overexpressed in 25 of 58 (43.1%); cytokeratin 5/6 was expressed in 14 of 54 (25.9%); estrogen receptor-beta was expressed in 37 of 56 (66.1%); HMGA2 was expressed in 29 of 63 (46.0%); and PLAG1 was expressed in 0 of 62 (0%). In addition, there was no statistically significant difference in the age at onset between patients with HMGA2-positive SDCs (range 32-85 years; mean: 64.3 years; median: 64.5 years) and those with HMGA2-negative SDCs (range 41-79 years; mean: 62.5 years; median: 64.5 years). There was also no statistically significant difference in overall survival between patients with HMGA2-positive and HMGA2-negative SDCs (follow-up period range 3-201 months; mean: 49.8 months; median: 30 months). Among 10 patients with a definite PA component (SDC ex-PA), 6 were positive and 4 were negative for HMGA2. Our data were consistent with previous findings that AR and estrogen receptor-beta are expressed in most SDCs, whereas HER2/neu overexpression and loss of PTEN are expressed in a subset of SDCs. In our cohort of patients, HMGA2 was expressed in approximately half of SDCs. HMGA2 and PTEN are promising therapeutic targets for salivary gland tumors.

Recurrent rearrangements of the PLAG1 and HMGA2 genes in lacrimal gland pleomorphic adenoma and carcinoma ex pleomorphic adenoma

PURPOSE

Lacrimal gland tumours constitute a wide spectrum of neoplastic lesions that are histologically similar to tumours of the salivary gland. In the salivary gland, pleomorphic adenoma (PA) is frequently characterized by recurrent chromosomal rearrangements of the PLAG1 and HMGA2 genes, a genetic feature retained in carcinoma ex pleomorphic adenoma (ca-ex-PA) that makes it possible to distinguish ca-ex-PA from de novo carcinomas. However, whether PLAG1 and HMGA2 gene rearrangements are found in lacrimal gland PA and ca-ex-PA is not known.

METHODS

Twenty-one lacrimal gland PAs and four ca-ex-PAs were retrospectively reviewed and subjected to break-apart fluorescence in situ hybridization (FISH) for rearrangements of the PLAG1 gene. Cases without PLAG1 abnormalities were subjected to HMGA2 break-apart FISH. Immunohistochemical staining for PLAG1 and HMGA2 protein was performed and correlated with gene status.

RESULTS

Sixteen of 21 PAs showed rearrangement of PLAG1 and were all positive for PLAG1 protein. Two of the remaining five PAs showed rearrangement of HMGA2 and were the only cases positive for HMGA2 with immunohistochemistry. The three FISH-negative PAs expressed PLAG1 protein. All four ca-ex-PAs showed rearrangement of PLAG1 and expressed PLAG1 protein. None of the de novo carcinomas showed rearrangement of either of the two genes or expression of the two proteins.

CONCLUSION

Rearrangement of PLAG1 and HMGA2 and expression of the corresponding proteins are frequent and specific findings in lacrimal gland PA and ca-ex-PA. The mechanism for PLAG1 overexpression in FISH-negative PAs is yet to be clarified.

Mutations in microRNA processing genes in Wilms tumors derepress the IGF2 regulator PLAG1

Many childhood Wilms tumors are driven by mutations in the microRNA biogenesis machinery, but the mechanism by which these mutations drive tumorigenesis is unknown. Here we show that the transcription factor pleomorphic adenoma gene 1 (PLAG1) is a microRNA target gene that is overexpressed in Wilms tumors with mutations in microRNA processing genes. Wilms tumors can also overexpress PLAG1 through copy number alterations, and PLAG1 expression correlates with prognosis in Wilms tumors. PLAG1 overexpression accelerates growth of Wilms tumor cells in vitro and induces neoplastic growth in the developing mouse kidney in vivo. In both settings, PLAG1 transactivates insulin-like growth factor 2 (IGF2), a key Wilms tumor oncogene, and drives mammalian target of rapamycin complex 1 (mTORC1) signaling. These data link microRNA impairment to the PLAG1-IGF2 pathway, providing new insight into the manner in which common Wilms tumor mutations drive disease pathogenesis.

Submucosal Colonic Lipoblastoma Presenting With Colo-colonic Intussusception in an Infant

Lipoblastoma is a benign adipose tumor typically presenting in infancy in superficial soft tissues of extremities. Intestinal complications secondary to intraabdominal or retroperitoneal involvement are exceedingly rare. We describe a unique case of a primary intestinal lipoblastoma arising from the submucosa of the transverse colon in an otherwise healthy 18-month-old boy. He presented with a history of reducible rectal prolapse, rectal bleeding, and episodic abdominal pain and was initially treated for constipation. Imaging identified a short colo-colonic intussusception, confirmed at laparotomy, and a fatty mass thought to arise from the mesentery. Pathological examination of the resected transverse colon revealed a submucosal tumor composed of a mixture of mature adipose tissue, foci of myxoid mesenchymal tissue with desmin positive, HMGA2 negative spindle cells, and scattered lipoblasts, characteristic of lipoblastoma. Lipoblastoma should be considered as a potential albeit rare cause of intussusception in young children, where a pathologic lead point is infrequently identified.