Inflammatory leiomyosarcoma is a distinct tumor characterized by near-haploidization, few somatic mutations, and a primitive myogenic gene expression signature

ALK-rearranged Mesenchymal Neoplasms With Prominent Foamy/Pseudolipogenic Cell Morphology: Expanding the Phenotypic Spectrum of ALK Fusion Neoplasms and Report of Novel Fusion Partners

The category of ALK-rearranged mesenchymal neoplasms has been evolving rapidly, with reports of morphologically diverse lesions of cutaneous, soft tissue, and visceral origin. While some of these represent morphologically defined entities harboring recurrent ALK fusions (inflammatory myofibroblastic tumor and epithelioid fibrous histiocytoma), others are unclassified by morphology with variable overlap with the tyrosine kinase family of neoplasia and their underlying ALK fusions cannot be suspected based on morphology. We herein report 3 cases that expand the anatomic, morphologic, and genotypic spectrum of ALK-rearranged unclassified neoplasms. Patients were all adults aged 46 to 69 (median: 63) who presented with a mass located in the gingiva, subcutis of the back, and submucosal posterior pharyngeal wall. The tumor size ranged from 1 to 2.7 cm (median: 1.6). Conservative surgery was the treatment in all patients. Follow-up was available for one patient who remained disease-free at 14 months. Histologically, all tumors displayed large polygonal cells with foamy to granular and lipogenic-like microvacuolated copious cytoplasm and medium-sized round nuclei with 1 or 2 prominent nucleoli. Mitoses and necrosis were not seen. The initial diagnostic impression was PEComa, inflammatory rhabdomyoblastic tumor and unclassified pseudolipogenic neoplasm. Strong cytoplasmic ALK was detected by immunohistochemistry in all cases. Other positive markers include Cathepsin K (2/2), desmin (1/3), focal MyoD1 (1/1), focal SMA (1/3), and focal EMA (1/2). Targeted RNA sequencing revealed ALK fusions with exon 20 (2 cases) and exon 19 (one case) of ALK fused to RND3 (exon 3), SQSTM1 (exon 6), and desmin (intron 6). Methylation profiling in the desmin-fused case (initially diagnosed as inflammatory rhabdomyoblastic tumor) revealed an inflammatory myofibroblastic tumor match with a low confidence score of 0.5 and a flat copy number variation (CNV) profile. No NF1 mutation was detected in this case, altogether excluding an inflammatory rhabdomyoblastic tumor. Our study highlights and expands the morphologic and anatomic diversity of ALK-fused neoplasms and documents novel fusion partners (RND3 and desmin).

Diffuse Pleural Mesotheliomas with Genomic Near-Haploidization: A Newly Recognized Subset with Distinct Clinical, Histologic, and Molecular Features

PURPOSE

Diffuse pleural mesotheliomas (DPM) with genomic near-haploidization (GNH) represent a novel subtype first recognized by The Cancer Genome Atlas project; however, its clinicopathologic and molecular features remain poorly defined.

EXPERIMENTAL DESIGN

We analyzed clinical genomic profiling data from 290 patients with DPM using the Memorial Sloan Kettering-Integrated Mutation Profiling of Actionable Cancer Targets (MSK-IMPACT) assay. Allele-specific copy number analysis was performed using the Fraction and Allele-Specific Copy Number Estimates from Tumor Sequencing (FACETS) algorithm.

RESULTS

A total of 210 patients were evaluable for loss of heterozygosity (LOH) analysis using FACETS from MSK-IMPACT tumor:normal sequencing data. In this cohort, GNH, defined as LOH across >80% of the genome, was detected in 10 cases (4.8%). Compared with non-GNH tumors, GNH DPMs were associated with younger age and less frequent self-reported history of occupational asbestos exposure. Histologically, GNH DPMs were enriched in biphasic subtype (80% vs. 14.5%) and showed abundant tumor-infiltrating lymphocytes (TILs). Genomic analysis revealed a higher frequency of TP53 alterations, whereas SETDB1 mutations were present in nearly all and only in this subset. The clinicopathologic and molecular findings were further validated in a separate cohort. Despite the younger age, patients with GNH DPMs had a shorter overall survival (10.9 vs. 25.4 months, P = 0.004); the poor prognostic impact of GNH remained significant after controlling for biphasic histology. Of three patients with GNH DPMs who received immune checkpoint blockade, two achieved a clinician-assessed partial response.

CONCLUSIONS

GNH defines an aggressive subtype of mainly biphasic DPMs in younger patients with recurrent alterations in SETDB1 and TP53. The enrichment in biphasic histology and TILs, together with our preliminary immune checkpoint blockade response data and anecdotal clinical trial data, suggests that further evaluation of immunotherapy may be warranted in this subset.

[Innovations in the classification of soft tissue tumors]

Soft tissue tumors are a very heterogeneous group of tumors. Their classification is regularly updated by the World Health Organization (WHO), most recently in 2020. The current classification of soft tissue tumors emphasizes molecular biological tumor characteristics, which enable tumor-specific treatment. In addition to Ewing's sarcoma, which occurs as bone as well as extra-skeletal soft tissue tumors as a small round cell sarcoma, three other subtypes of undifferentiated, small and round cell sarcomas have been introduced. Some names of the new sarcomas can be derived from the gene mutations. The groups of adipocytic and (myo)fibroblastic tumors have been extended by three further entities. There were further additions to vascular soft tissue tumors, smooth muscle cell tumors, peripheral nerve sheath tumors and tumors of uncertain differentiation. A distinction is made between benign, intermediate locally aggressive, intermediate rarely metastatic and malignant soft tissue tumors.

Inflammatory rhabdomyoblastic tumor, pheochromocytoma, and pulmonary hamartoma in a patient with neurofibromatosis type 1: a case report

BACKGROUND

Inflammatory rhabdomyoblastic tumors are relatively recently recognized soft tissue tumors with a low malignant potential. Here, we present a case of concurrent inflammatory rhabdomyoblastic tumor (IRMT), adrenal pheochromocytoma, and pulmonary hamartoma in a patient with neurofibromatosis type 1 (NF1). To our knowledge, this is the first time that this constellation of tumors has been described in the literature.

CASE PRESENTATION

A female patient in her late 20s with known NF1 was diagnosed with an inflammatory rhabdomyoblastic tumor, pheochromocytoma, and pulmonary hamartoma in a short succession. IRMT was found to harbor a near-haploid genome and displayed a typical immunohistochemical profile as well as a focal aberrant p53 expression pattern.

CONCLUSIONS

This case report strengthens the theory that defects in the tumor suppressor NF1 play a central role in the pathogenesis of inflammatory rhabdomyoblastic tumors and that IRMT may be part of the spectrum of neurofibromatosis type 1 related tumors.

Myxoid Pleomorphic Liposarcoma

Myxoid pleomorphic liposarcoma (MPLPS) shows a strong predilection for the mediastinum and can affect a wide age range. Clinically, MPLPS exhibits aggressive behavior and demonstrates a worse overall and progression-free survival than myxoid/round cell liposarcoma (MRLPS) and pleomorphic liposarcoma (PLPS). Histologically, MPLPS is characterized by hybrid morphologic features of MRLPS and PLPS, including myxoid stroma, chicken wire-like vasculature, univacuolated and multivacuolated lipoblasts, and high-grade pleomorphic sarcomatous components. In terms of molecular features, MPLPS is distinct from other lipomatous tumors as it harbors genome-wide loss of heterozygosity.

Inflammatory Rhabdomyoblastic Tumor: From a Nebulous Smooth Muscle Neoplasm to a Novel Skeletal Muscle Tumor Subtype

Inflammatory rhabdomyoblastic tumor is a recently introduced name for neoplasms currently included in the World Health Organization classification of soft tissue tumors under the rubric inflammatory leiomyosarcoma. Inflammatory rhabdomyoblastic tumor is an excellent example of how surgical pathologists working in conjunction with tumor biologists can greatly improve tumor classification to the benefit of patients. Over the last 28 years, understanding of this entity has undergone a fascinating evolution. This review serves as a summary of the latest findings in inflammatory rhabdomyoblastic tumor research and a diagnostic manual for the practicing surgical pathologist.

Inflammatory Rhabdomyoblastic Tumor of the Posterior Pharyngeal Wall

This case report describes a healthy man in his 40s who presented with a 1-year history of snoring, sleep apnea, dysphonia, and dysphagia owing to a large mass of the posterior pharynx and was diagnosed with an inflammatory rhabdomyoblastic tumor.

Inflammatory Rhabdomyoblastic Tumor: Clinicopathologic and Molecular Analysis of 13 Cases

Inflammatory rhabdomyoblastic tumors (IRMTs) are newly recognized skeletal muscle tumors with uncertain malignant potential. We investigated 13 IRMTs using clinicopathologic, genetic, and epigenetic methods. The cohort included 7 men and 6 women, aged 23 to 80 years (median, 50 years), of whom 2 had neurofibromatosis type 1. Most tumors occurred in the deep soft tissues of the lower limbs, head/neck, trunk wall, and retroperitoneum/pelvis. Two tumors involved the hypopharyngeal submucosa as polypoid masses. Eight tumors showed conventional histology of predominantly spindled cells with nuclear atypia, low mitotic activity, and massive inflammatory infiltrates. Three tumors showed atypical histology, including uniform epithelioid or plump cells and mitotically active histiocytes. The remaining 2 tumors demonstrated malignant progression to rhabdomyosarcoma; one had additional IRMT histology and the other was a pure sarcoma. All 11 IRMTs without malignant progression exhibited indolent behavior at a median follow-up of 43 months. One of the 2 patients with IRMTs with malignant progression died of lung metastases. All IRMTs were positive for desmin and PAX7, whereas myogenin and MyoD1 were expressed in a subset of cases. Targeted next-generation sequencing identified pathogenic mutations in NF1 (5/8) and TP53 (4/8). All TP53 mutations co-occurred with NF1 mutations. TP53 variant allele frequency was much lower than that of NF1 in 2 cases. These tumors showed geographic (subclonal) strong p53 immunoreactivity, suggesting the secondary emergence of a TP53-mutant clone. DNA methylation-based copy number analysis conducted in 11 tumors revealed characteristic flat patterns with relative gains, including chromosomes 5, 18, 20, 21, and/or 22 in most cases. Widespread loss of heterozygosity with retained biparental copies of these chromosomes was confirmed in 4 tumors analyzed via allele-specific profiling. Based on unsupervised DNA methylation analysis, none of the 11 tumors tested clustered with existing reference entities but formed a coherent group, although its specificity warrants further study.

Pulmonary inflammatory leiomyosarcoma represents a potential diagnostic pitfall of DNA methylation-based classification of sarcomas: a case report

BACKGROUND

Pulmonary inflammatory leiomyosarcoma (PILMS) is a rare type of myogenic tumor with prominent lymphohistiocytic infiltration. Despite their histological similarities, PILMS is immunohistochemically and genetically distinct from soft tissue inflammatory leiomyosarcoma, and its clinicopathological picture including DNA methylome data remains still unknown.

CASE PRESENTATION

Here we present a case of PILMS in an 18-year-old male who underwent lobectomy. As reported previously, the current case demonstrated spindle myoid cell proliferation with smooth muscle differentiation within a prominent lymphohistiocytic infiltration and a diploid genome with a MUC3A gene alteration. DNA methylation analysis predicted this case to be an "inflammatory myofibroblastic tumor" (IMT) according to the Deutsches Krebsforschungszentrum (DKFZ) classifier. The data was analyzed by t-distributed stochastic neighbor embedding, which plotted the case tumor in the vicinity of IMT, however, there were no IMT histological features. These discordant results could be due to background non-neoplastic inflammatory cells.

CONCLUSIONS

As the DNA methylation classification of PILMS might be a potential diagnostic pitfall, an integrative histological and genetic approach is required for its accurate diagnosis.

The spectrum and significance of secondary (co-occurring) genetic alterations in sarcomas: the hallmarks of sarcomagenesis

Bone and soft tissue tumors are generally classified into complex karyotype sarcomas versus those with recurrent genetic alterations, often in the form of gene fusions. In this review, we provide an overview of important co-occurring genomic alterations, organized by biological mechanisms and covering a spectrum of genomic alteration types: mutations (single-nucleotide variations or indels) in oncogenes or tumor suppressor genes, copy number alterations, transcriptomic signatures, genomic complexity indices (e.g. CINSARC), and complex genomic structural variants. We discuss the biological and prognostic roles of these so-called secondary or co-occurring alterations, arguing that recognition and detection of these alterations may be significant for our understanding and management of mesenchymal tumors. On a related note, we also discuss major recurrent alterations in so-called complex karyotype sarcomas. These secondary alterations are essential to sarcomagenesis via a variety of mechanisms, such as inactivation of tumor suppressors, activation of proliferative signal transduction, telomere maintenance, and aberrant regulation of epigenomic/chromatin remodeling players. The use of comprehensive genomic profiling, including targeted next-generation sequencing panels or whole-exome sequencing, may be incorporated into clinical workflows to offer more comprehensive, potentially clinically actionable information. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Rhabdomyosarcoma Arising in Inflammatory Rhabdomyoblastic Tumor: A Genetically Distinctive Subtype of Rhabdomyosarcoma

"Inflammatory rhabdomyoblastic tumor" (IRMT) is a recently coined name for a distinctive soft tissue neoplasm characterized by slow growth, a dense histiocytic infiltrate, scattered, bizarre-appearing tumor cells with morphologic and immunohistochemical evidence of skeletal muscle differentiation, a near-haploid karyotype with retained biparental disomy of chromosomes 5 and 22, and usually indolent behavior. There are 2 reports of rhabdomyosarcoma (RMS) arising in IRMT. We studied the clinicopathologic and cytogenomic features of 6 cases of IRMT with progression to RMS. Tumors occurred in the extremities of 5 men and 1 woman (median patient age, 50 years; median tumor size, 6.5 cm). Clinical follow-up (6 patients: median, 11 months; range 4-163 months) documented local recurrence and distant metastases in 1 and 5 of 6 patients, respectively. Therapy included complete surgical resection (4 patients) and adjuvant/neoadjuvant chemo/radiotherapy (6 patients). One patient died of disease, 4 were alive with metastatic disease, and one was without evidence of disease. All primary tumors contained conventional IRMT. Progression to RMS appeared as follows: (1) overgrowth of monomorphic rhabdomyoblasts with diminished histiocytes, (2) monomorphic spindle cell morphology with variably pleomorphic rhabdomyoblasts and low mitotic activity, or (3) morphologically undifferentiated spindle cell and epithelioid sarcoma. All but one were diffusely desmin-positive, with more limited MyoD1/myogenin expression. All RMS arising in IRMT, either primary or metastatic, demonstrated widespread loss of heterozygosity with retained heterozygosity of chromosomes 5 and 20, and all but one displayed additional gains and losses involving loci containing oncogenes/ tumor suppressor genes, most often CDKN2A and CDKN2B. RMS arising in IRMT have unique clinicopathologic and cytogenomic features, warranting classification as a distinct, potentially aggressive RMS subtype. It should be distinguished from other RMSs, particularly fusion-driven spindle cell RMS and pleomorphic RMS.

Fine-needle aspiration biopsy diagnosis of histiocyte-rich rhabdomyoblastic tumor (inflammatory leiomyosarcoma): A case report

Histiocyte-rich rhabdomyoblastic tumor (HRRMT) is an exceedingly rare soft tissue tumor of primitive myogenic differentiation. We report herein a case involving the soft tissue in the left lateral peri-scapular region in a 68-year-old female with a 2-month history of a non-painful soft tissue mass. Ultrasound revealed a solid, ovoid subcutaneous mass lesion that lacked significant internal vascularity. Percutaneous fine-needle aspiration (FNA) biopsy with concomitant core needle biopsy was performed, and a diagnosis of HRRMT was rendered. Cytologic smears were hypercellular, composed of a mixture of foamy histiocytes and a variably cohesive population of epithelioid and plasmacytoid to vaguely spindled cells in cohesive clusters and singly dispersed. Histologic material showed sheets of epithelioid and plasmacytoid to spindled cells with admixed foamy histiocytes with distended, vacuolated cytoplasm. To our knowledge, this is the first reported example of HRRMT evaluated by FNA biopsy.

[Changes in the WHO classification (2020) of soft tissue tumors]

The article provides an overview of the main changes in the current (2020) WHO classification of soft tissue tumors, as well as selected updates that have occurred since the release of the classification.

Myxoid pleomorphic liposarcoma is distinguished from other liposarcomas by widespread loss of heterozygosity and significantly worse overall survival: a genomic and clinicopathologic study

Myxoid pleomorphic liposarcoma (MPLPS) is a recently described and extremely rare subtype of liposarcoma with a predilection for the mediastinum. However, the genomic features of MPLPS remain poorly understood. We performed comprehensive genomic profiling of MPLPS in comparison with pleomorphic liposarcoma (PLPS) and myxoid/round cell liposarcoma (MRLPS). Of the 8 patients with MPLPS, 5 were female and 3 were male, with a median age of 32 years old (range 10-68). All except one were located in the mediastinum, with invasion of surrounding anatomic structures, including chest wall, pleura, spine, and large vessels. All cases showed an admixture of morphologies reminiscent of PLPS and MRLPS, including myxoid areas with plexiform vasculature admixed with uni- and/or multivacuolated pleomorphic lipoblasts. Less common features included well-differentiated liposarcoma-like areas, and in one case fascicular spindle cell sarcoma reminiscent of dedifferentiated LPS. Clinically, 4 experienced local recurrence, 4 had distant metastases and 5 died of disease. Compared to PLPS and MRLPS, patients with MPLPS had worse overall and progression-free survival. Recurrent TP53 mutations were present in all 8 MPLPS cases. In contrast, in PLPS, which also showed recurrent TP53 mutations (83%), RB1 and ATRX losses were more common. MRLPS was highly enriched in TERT promoter mutations (88%) and PI3K/AKT pathway mutations. Copy number profiling in MPLPS revealed multiple chromosomal gains with recurrent amplifications of chromosomes 1, 19 and 21. Importantly, allele-specific copy number analysis revealed widespread loss of heterozygosity (80% of the genome on average) in MPLPS, but not in PLPS or MRLPS. Our findings revealed genome-wide loss of heterozygosity co-existing with TP53 mutations as a characteristic genomic signature distinct from other liposarcoma subtypes, which supports the current classification of MPLPS as a stand-alone pathologic entity. These results further expand the clinicopathologic features of MPLPS, including older age, extra-mediastinal sites, and a highly aggressive outcome.

Inflammatory leiomyosarcoma/rhabdomyoblastic tumor: a report of two cases with novel genetic findings

Inflammatory leiomyosarcoma (ILMS) is a malignant neoplasm showing smooth muscle differentiation, a prominent inflammatory infiltrate, and near‐haploidization. These tumors have significant pathologic and genetic overlap with the recently described “inflammatory rhabdomyoblastic tumor (IRT),” suggesting that ILMS and IRT may belong to one entity. Herein, we describe two cases of ILMS/IRT with attention to new cytogenetic and sequencing findings. The tumors were composed of sheets and fascicles of variably pleomorphic tumor cells showing spindled and epithelioid to rhabdoid morphology and a prominent histiocyte‐rich inflammatory infiltrate typical of ILMS/IRT. In case 1, chromosomal microarray analysis showed a near‐haploid pattern with loss of heterozygosity resulting from loss of one copy of all autosomes except for chromosomes 5, 20, 21, and 22. Case 2 showed areas with high‐grade rhabdomyosarcomatous transformation. In this case, the low‐grade tumor component revealed a hyper‐diploid pattern with loss of heterozygosity for most of autosomes but with a normal diploid copy number state except for chromosomes 5, 20, and 22, which showed a relative gain. The high‐grade tumor component showed a similar pattern of copy‐neutral loss of heterozygosity with additional abnormalities, including mosaic segmental gains at 1p, 5p, 8q, 9p, 20q, and segmental loss at 8p. Next‐generation sequencing identified sequence variants in NF1, TP53, SMARCA4, KRAS, and MSH6. MSH6 variant was confirmed as germline, consistent with the diagnosis of hereditary nonpolyposis colorectal cancer (HNPCC) syndrome in one of our study patients and suggestive that ILMS/IRT might be part of the HNPCC cancer spectrum.

Clinicopathologic and Genomic Characterization of Inflammatory Myofibroblastic Tumors of the Head and Neck: Highlighting a Novel Fusion and Potential Diagnostic Pitfall

Inflammatory myofibroblastic tumor (IMT) is a distinctive fibroblastic and myofibroblastic spindle cell neoplasm with an accompanying inflammatory cell infiltrate and frequent receptor tyrosine kinase activation at the molecular level. The tumor may recur and rarely metastasizes. IMT is rare in the head and neck region, and limited information is available about its clinicopathologic and molecular characteristics in these subsites. Therefore, we analyzed a cohort of head and neck IMTs through a multi-institutional approach. Fourteen cases were included in the provisional cohort, but 1 was excluded after molecular analysis prompted reclassification. Patients in the final cohort included 7 males and 6 females, with a mean age of 26.5 years. Tumors were located in the larynx (n=7), oral cavity (n=3), pharynx (n=2), and mastoid (n=1). Histologically, all tumors showed neoplastic spindle cells in storiform to fascicular patterns with associated chronic inflammation, but the morphologic spectrum was wide, as is characteristic of IMT in other sites. An underlying fusion gene event was identified in 92% (n=11/12) of cases and an additional case was ALK-positive by IHC but could not be evaluated molecularly. ALK represented the driver in all but 1 case. Rearrangement of ALK, fused with the TIMP3 gene (n=6) was most commonly detected, followed by 1 case each of the following fusion gene partnerships: TPM3-ALK, KIF5B-ALK, CARS-ALK, THBS1-ALK, and a novel alteration, SLC12A2-ROS1. The excluded case was reclassified as spindle cell rhabdomyosarcoma after detection of a FUS-TFCP2 rearrangement and retrospective immunohistochemical confirmation of rhabdomyoblastic differentiation, illustrating an important diagnostic pitfall. Two IMT patients received targeted therapy with crizotinib, with a demonstrated radiographic response. One tumor recurred but none metastasized. These results add to the growing body of evidence that kinase fusions can be identified in the majority of IMTs and that molecular analysis can lead to increased diagnostic accuracy and broadened therapeutic options for patients.

WHO classification of soft tissue tumours 2020: An update and simplified approach for radiologists

The WHO classification of soft tissue tumours categorizes the lesions based on histological differentiation. In the recent fifth edition (2020), many new entities have been introduced, based on their distinct biological behaviour, genetics and morphology. With the recent advances and better understanding of molecular genetics, several novel recurrent genetic alterations have been incorporated in this edition. These may serve as reliable diagnostic and prognostic markers for various soft tissue tumours. Though predominantly a pathologist's game; the radiologists must be aware of the recent updates to contribute towards the optimal diagnosis and management of soft tissue tumours. The imaging features of the new entities have not yet been described but are expected to be explored in the coming years. We hereby present a concise review of the updates in the recent WHO classification of soft tissue tumours. We have tried to emphasize the novel molecular genetics and their surrogate immunohistochemical markers which have brought a paradigm shift in the diagnosis, therapeutics, and prognosis of soft tissue tumours. We also present simplified diagnostic algorithms to characterize soft tissue tumours based on the clinico-radiological features.

Staging and Classification of Primary Musculoskeletal Bone and Soft Tissue Tumors Based on the 2020 WHO Update, From the AJR Special Series on Cancer Staging

Staging of primary musculoskeletal bone and soft tissue tumors is most commonly performed using the AJCC and the Enneking or Musculoskeletal Tumor Society (MSTS) staging systems. Radiologic imaging is integral in achieving adequate musculoskeletal neoplastic staging by defining lesion extent and identifying regional lymph node involvement and distant metastatic disease. Additional important features in surgical planning, though not distinct components of the staging systems, include cortical involvement, joint invasion, and neurovascular encasement; these features are optimally evaluated by MRI. In 2020, the WHO updated the classification of primary musculoskeletal tumors of soft tissue and bone. The update reflects the continued explosion in identification of novel gene alterations in many bone and soft tissue neoplasms. This has resulted in newly designated lesions, reclassification of lesion categories, and improved specificity of diagnosis. While radiologists do not need to have a comprehensive knowledge of the pathologic details, a broad working understanding of the most recent update is important to aid accurate and timely diagnosis given that histologic grading is a component of all staging systems. By approaching primary musculoskeletal neoplasms through a multidisciplinary approach with colleagues in pathology, orthopedic oncology, radiation oncology, and medical oncology, radiologists may promote improved diagnosis, treatment, and outcomes.

"Inflammatory Leiomyosarcoma" and "Histiocyte-rich Rhabdomyoblastic Tumor": a clinicopathological, immunohistochemical and genetic study of 13 cases, with a proposal for reclassification as "Inflammatory Rhabdomyoblastic Tumor"

Inflammatory leiomyosarcoma (ILMS), defined as "a malignant neoplasm showing smooth muscle differentiation, a prominent inflammatory infiltrate, and near-haploidization", is a very rare soft tissue tumor with a generally favorable prognosis. The morphologic features of "histiocyte-rich rhabdomyoblastic tumor" (HRRMT) are similar to those of ILMS, although this lesion shows by definition a skeletal muscle phenotype. Recent gene expression profiling and immunohistochemical studies have also suggested that ILMS and HRRMT may be related. We studied the clinicopathologic, immunohistochemical and genetic features of four cases previously classified as ILMS and nine classified as HRRMT. Tumors from both groups tended to occur in the deep soft tissues of the extremities of young to middle-aged males and exhibited indolent behavior. Morphologically, all were well-circumscribed, often encapsulated, and showed a striking histiocyte-rich inflammatory infiltrate admixed with variably pleomorphic tumor cells showing spindled and epithelioid to rhabdoid morphology, eosinophilic cytoplasm, and prominent nucleoli, but few, if any, mitotic figures. Immunohistochemically, the tumor cells expressed desmin, alpha-smooth muscle actin, and the rhabdomyoblastic markers PAX7, MyoD1, and myogenin. H-caldesmon expression was absent in all cases, using the specific h-CD antibody. Karyotypic study (1 HRRMT) and genome-wide copy number analysis (7 HRRMT, OncoScan SNP assay), revealed near-haploidization in four cases, with subsequent genome doubling in one, an identical phenotype to that seen in ILMS. We propose reclassification of ILMS and HRRMT as "inflammatory rhabdomyoblastic tumor", a name which accurately describes the salient morphologic and immunohistochemical features of this distinctive tumor, as well as its intermediate (rarely metastasizing) clinical behavior.

The 2020 WHO Classification: What's New in Soft Tissue Tumor Pathology?

The fifth edition of the World Health Organization Classification of Tumors of Soft Tissue and Bone was published in early 2020. The revisions reflect a consensus among an international expert editorial board composed of soft tissue and bone pathologists, geneticists, a medical oncologist, surgeon, and radiologist. The changes in the soft tissue tumor chapter notably include diverse, recently described tumor types (eg, atypical spindle cell/pleomorphic lipomatous tumor, angiofibroma of soft tissue, and CIC-rearranged sarcoma), new clinically significant prognostic information for a variety of existing entities (eg, dedifferentiated liposarcoma and solitary fibrous tumor), and a plethora of novel genetic alterations, some of practical diagnostic relevance (eg, NAB2-STAT6 in solitary fibrous tumor, FOSB rearrangements in epithelioid hemangioma and pseudomyogenic hemangioendothelioma, and SUZ12 or EED mutations in malignant peripheral nerve sheath tumor, leading to loss of H3K27 trimethylation). In this review, we highlight the major changes to the soft tissue chapter in the 2020 World Health Organization Classification, as well as the new chapter on undifferentiated small round cell sarcomas, with a focus on updates in diagnostic categories, prognostication, and novel markers. Recent discoveries in molecular genetics are also discussed, particularly those of immediate utility in differential diagnosis, including protein correlates detectable using immunohistochemistry.

Updates from the 2020 World Health Organization Classification of Soft Tissue and Bone Tumours

The fifth edition of the World Health Organization (WHO) classification of soft tissue and bone tumours was published in May 2020. This 'Blue Book', which is also available digitally for the first time, incorporates an array of new information on these tumours, amassed in the 7 years since the previous edition. Major advances in molecular characterisation have driven further refinements in classification and the development of ancillary diagnostic tests, and have improved our understanding of disease pathogenesis. Several new entities are also included. This review summarises the main changes introduced in the 2020 WHO classification for each subcategory of soft tissue and bone tumours.

Genetics, Diagnosis, and Management of Hürthle Cell Thyroid Neoplasms

Hürthle cell lesions have been a diagnostic conundrum in pathology since they were first recognized over a century ago. Controversy as to the name of the cell, the origin of the cell, and even which cells in particular may be designated as such still challenge pathologists and confound those treating patients with a diagnosis of "Hürthle cell" anything within the diagnosis, especially if that anything is a sizable mass lesion. The diagnosis of Hürthle cell adenoma (HCA) or Hürthle cell carcinoma (HCC) has typically relied on a judgement call by pathologists as to the presence or absence of capsular and/or vascular invasion of the adjacent thyroid parenchyma, easy to note in widely invasive disease and a somewhat subjective diagnosis for minimally invasive or borderline invasive disease. Diagnostic specificity, which has incorporated a sharp increase in molecular genetic studies of thyroid tumor subtypes and the integration of molecular testing into preoperative management protocols, continues to be challenged by Hürthle cell neoplasia. Here, we provide the improving yet still murky state of what is known about Hürthle cell tumor genetics, clinical management, and based upon what we are learning about the genetics of other thyroid tumors, how to manage expectations, by pathologists, clinicians, and patients, for more actionable, precise classifications of Hürthle cell tumors of the thyroid.

The 2020 WHO Classification of Tumors of Soft Tissue: Selected Changes and New Entities

Soft tissue tumors are a relatively rare and diagnostically challenging group of neoplasms that can have varying lines of differentiation. Accurate diagnosis is important for appropriate treatment and prognostication. In the 8 years since the publication of the 4th Edition of World Health Organization (WHO) classification of soft tissue tumors, significant advances have been made in our understanding of soft tissue tumor molecular biology and diagnostic criteria. The 5th Edition of the 2020 WHO classification of tumors of soft tissue and bone incorporated these changes. Classification of tumors, in general, but particularly in soft tissue tumors, is increasingly based on the molecular characteristics of tumor types. Understanding tumor molecular genetics improves diagnostic accuracy for tumors that have been difficult to classify on the basis of morphology alone, or that have overlapping morphologic features. In many large hospitals in the United States and Europe, molecular tests on soft tissue tumors are a routine part of diagnosis. Therefore, surgical pathologists should be familiar with newly emerging molecular genetic techniques in clinical settings. In the near future, molecular tests, particularly in soft tissue tumor diagnosis, will become as routine during diagnosis as immunohistochemistry is currently. This new edition provides an updated classification scheme and essential diagnostic criteria for soft tissue tumors. Newly recognized entities and subtypes of existing tumor types, several reclassified tumors, and newly defined molecular and genetic data have been incorporated. Herein, we summarize the updates in the WHO 5th Edition, focusing on major changes in each category of soft tissue tumor, and the newly described tumor entities and subtypes.

Near haploidization is a genomic hallmark which defines a molecular subgroup of giant cell glioblastoma

Background

Giant cell glioblastoma (gcGBM) is a rare histologic subtype of glioblastoma characterized by numerous bizarre multinucleate giant cells and increased reticulin deposition. Compared with conventional isocitrate dehydrogenase (IDH)-wildtype glioblastomas, gcGBMs typically occur in younger patients and are generally associated with an improved prognosis. Although prior studies of gcGBMs have shown enrichment of genetic events, such as TP53 alterations, no defining aberrations have been identified. The aim of this study was to evaluate the genomic profile of gcGBMs to facilitate more accurate diagnosis and prognostication for this entity.

Methods

Through a multi-institutional collaborative effort, we characterized 10 gcGBMs by chromosome studies, single nucleotide polymorphism microarray analysis, and targeted next-generation sequencing. These tumors were subsequently compared to the genomic and epigenomic profile of glioblastomas described in The Cancer Genome Atlas (TCGA) dataset.

Results

Our analysis identified a specific pattern of genome-wide massive loss of heterozygosity (LOH) driven by near haploidization in a subset of glioblastomas with giant cell histology. We compared the genomic signature of these tumors against that of all glioblastomas in the TCGA dataset (n = 367) and confirmed that our cohort of gcGBMs demonstrated a significantly different genomic profile. Integrated genomic and histologic review of the TCGA cohort identified 3 additional gcGBMs with a near haploid genomic profile.

Conclusions

Massive LOH driven by haploidization represents a defining molecular hallmark of a subtype of gcGBM. This unusual mechanism of tumorigenesis provides a diagnostic genomic hallmark to evaluate in future cases, may explain reported differences in survival, and suggests new therapeutic vulnerabilities.

The 2020 WHO Classification of Soft Tissue Tumours: news and perspectives

Mesenchymal tumours represent one of the most challenging field of diagnostic pathology and refinement of classification schemes plays a key role in improving the quality of pathologic diagnosis and, as a consequence, of therapeutic options. The recent publication of the new WHO classification of Soft Tissue Tumours and Bone represents a major step toward improved standardization of diagnosis. Importantly, the 2020 WHO classification has been opened to expert clinicians that have further contributed to underline the key value of pathologic diagnosis as a rationale for proper treatment. Several relevant advances have been introduced. In the attempt to improve the prediction of clinical behaviour of solitary fibrous tumour, a risk assessment scheme has been implemented. NTRK-rearranged soft tissue tumours are now listed as an "emerging entity" also in consideration of the recent therapeutic developments in terms of NTRK inhibition. This decision has been source of a passionate debate regarding the definition of "tumour entity" as well as the consequences of a "pathology agnostic" approach to precision oncology. In consideration of their distinct clinicopathologic features, undifferentiated round cell sarcomas are now kept separate from Ewing sarcoma and subclassified, according to the underlying gene rearrangements, into three main subgroups (CIC, BCLR and not ETS fused sarcomas) Importantly, In order to avoid potential confusion, tumour entities such as gastrointestinal stroma tumours are addressed homogenously across the different WHO fascicles. Pathologic diagnosis represents the integration of morphologic, immunohistochemical and molecular characteristics and is a key element of clinical decision making. The WHO classification is as a key instrument to promote multidisciplinarity, stimulating pathologists, geneticists and clinicians to join efforts aimed to translate novel pathologic findings into more effective treatments.

Investigating the Role of Telomere and Telomerase Associated Genes and Proteins in Endometrial Cancer

Endometrial cancer (EC) is the commonest gynaecological malignancy. Current prognostic markers are inadequate to accurately predict patient survival, necessitating novel prognostic markers, to improve treatment strategies. Telomerase has a unique role within the endometrium, whilst aberrant telomerase activity is a hallmark of many cancers. The aim of the current in silico study is to investigate the role of telomere and telomerase associated genes and proteins (TTAGPs) in EC to identify potential prognostic markers and therapeutic targets. Analysis of RNA-seq data from The Cancer Genome Atlas identified differentially expressed genes (DEGs) in EC (568 TTAGPs out of 3467) and ascertained DEGs associated with histological subtypes, higher grade endometrioid tumours and late stage EC. Functional analysis demonstrated that DEGs were predominantly involved in cell cycle regulation, while the survival analysis identified 69 DEGs associated with prognosis. The protein-protein interaction network constructed facilitated the identification of hub genes, enriched transcription factor binding sites and drugs that may target the network. Thus, our in silico methods distinguished many critical genes associated with telomere maintenance that were previously unknown to contribute to EC carcinogenesis and prognosis, including NOP56, WFS1, ANAPC4 and TUBB4A. Probing the prognostic and therapeutic utility of these novel TTAGP markers will form an exciting basis for future research.

Histiocyte-rich rhabdomyoblastic tumor: a report of two cases and a review of the differential diagnoses

Histiocyte-rich rhabdomyoblastic tumor is a recently described skeletal muscle neoplasm of uncertain malignant potential, characterized by slow growth, a fibrous capsule containing peripheral lymphoid aggregates, spindle-to-epithelioid cells with a rhabdomyoblastic immunophenotype, and a dense histiocytic infiltrate. It most commonly arises within the muscles of the lower legs and trunk in young-to-middle-aged men, and initial reports suggest indolent behavior. In this paper, we present two additional cases of histiocyte-rich rhabdomyoblastic tumor with similar clinicopathologic features and discuss the differential diagnosis including its overlap with inflammatory leiomyosarcoma.

Inflammatory leiomyosarcoma shows frequent co-expression of smooth and skeletal muscle markers supporting a primitive myogenic phenotype: a report of 9 cases with a proposal for reclassification as low-grade inflammatory myogenic tumor

Inflammatory leiomyosarcoma (ILMS) is a very rare soft tissue tumor that usually follows an indolent clinical course, but long-term follow-up studies are lacking. Recent publications primarily focused on its genetic profile characterized by a near haploid genome. One study also showed these tumors to have upregulation of genes known to be crucial for skeletal muscle differentiation. Nevertheless, immunohistochemical expression of skeletal muscle markers, as well as markers that would help to distinguish ILMS from a long list of relevant differential diagnostic entities, has not been extensively studied. Nine cases of ILMS were collected and stained by a broad IHC panel which, besides others, contained MyoD1, myogenin, and PAX-7. A subset of cases was also analyzed by 2 different NGS assays and by MDM2 fluorescence in situ hybridization. Five male and 4 female patients ranged in age from 25 to 54 years (mean, 36 years). The tumors showed a predilection for intramuscular sites of the lower limbs (n = 4) and back (n = 2), whereas the remaining 3 cases affected an unspecified skeletal muscle, lung, and omentum. Follow-up with an average length of 10.6 years (range 0.5-22) was available for 8 patients. The omental tumor spread locally within the abdominal cavity, but the patient has been free of disease 7 years after treatment. None of the 5 patients with somatic soft tissue tumors (and follow-up longer than 1.5 years) had either recurrence or metastasis. Immunohistochemical studies revealed a substantial expression of skeletal muscle markers in almost all cases. This phenotype coupled with a highly characteristic genotype and significantly more indolent clinical behavior as compared with conventional leiomyosarcoma of deep soft tissue offers a strong rationale to change the current nomenclature. Based on the clinicopathological features and gene expression profile, we propose the name low-grade inflammatory myogenic tumor.

Molecular characterization of localized pleural mesothelioma

Localized pleural mesothelioma is a rare solitary circumscribed pleural tumor that is microscopically similar to diffuse malignant pleural mesothelioma. However, the molecular characteristics and nosologic relationship with its diffuse counterpart remain unknown. In a consecutive cohort of 1110 patients with pleural mesotheliomas diagnosed in 2005-2018, we identified six (0.5%) patients diagnosed with localized pleural mesotheliomas. We gathered clinical history, evaluated the histopathology, and in select cases performed karyotypic analysis and targeted next-generation sequencing. The cohort included three women and three men (median age 63; range 28-76), often presenting incidentally during radiologic evaluation for unrelated conditions. Neoadjuvant chemotherapy was administered in two patients. All tumors (median size 5.0 cm; range 2.7-13.5 cm) demonstrated gross circumscription (with microscopic invasion into lung, soft tissue, and/or rib in four cases), mesothelioma histology (four biphasic and two epithelioid types), and mesothelial immunophenotype. Of four patients with at least 6-month follow-up, three were alive (up to 8.9 years). Genomic characterization identified several subgroups: (1) BAP1 mutations with deletions of CDKN2A and NF2 in two tumors; (2) TRAF7 mutations in two tumors, including one harboring trisomies of chromosomes 3, 5, 7, and X; and (3) genomic near-haploidization, characterized by extensive loss of heterozygosity sparing chromosomes 5 and 7. Localized pleural mesotheliomas appear genetically heterogeneous and include BAP1-mutated, TRAF7-mutated, and near-haploid subgroups. While the BAP1-mutated subgroup is similar to diffuse malignant pleural mesotheliomas, the TRAF7-mutated subgroup overlaps genetically with adenomatoid tumors and well-differentiated papillary mesotheliomas, in which recurrent TRAF7 mutations have been described. Genomic near-haploidization, identified recently in a subset of diffuse malignant pleural mesotheliomas, suggests a novel mechanism in the pathogenesis of both localized pleural mesothelioma and diffuse malignant pleural mesothelioma. Our findings describe distinctive genetic features of localized pleural mesothelioma, with both similarities to and differences from diffuse malignant pleural mesothelioma.