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Myositis ossificans, a benign tumor composed of spindle cells and osteoblasts, can clinically and radiologically mimic osteosarcoma. While recognition and accurate diagnosis of myositis ossificans can be a challenge, this is critical as it may allow a conservative surgical approach to maximize functional outcomes. Herein, we present a patient with surface myositis ossificans confirmed genetically by the presence of COL1A1::USP6 gene fusion, along with a literature review. Due to the enhanced visualization of the bone matrix, computed tomography (CT) imaging may be a superior imaging modality to magnetic resonance (MR) imaging. Staged biopsies with samples obtained from the periphery and center of the lesions may allow pathologists to discern the zonal distribution histologically. Furthermore, immunohistochemistry fluorescence in situ hybridization and molecular testing can aid in the distinction of myositis ossificans from mimics. Because of their resemblance to other bone tumors, these cases of myositis ossificans highlight the importance of a multidisciplinary approach integrating clinical, radiologic, and pathologic analysis and involving serial imaging, sampling, and judicious use of ancillary immunohistochemical and molecular testing. [ABSTRACT FROM AUTHOR]

Diagnosis of desmoid-type fibromatosis (DF) may be challenging on biopsy due to morphologic overlap with reactive fibrosis (scar) and other uniform spindle cell neoplasms. Evaluation of nuclear β-catenin, a surrogate of Wnt pathway activation, is often difficult in DF due to weak nuclear expression and high background membranous/cytoplasmic staining. Lymphoid enhancer-factor 1 (LEF1) is a recently characterized effector partner of β-catenin which activates the transcription of target genes. We investigated the performance of LEF1 and β-catenin immunohistochemistry in a retrospective series of 156 soft tissue tumors, including 35 DF, 3 superficial fibromatosis, and 121 histologic mimics (19 soft tissue perineurioma, 8 colorectal perineurioma, 4 intraneural perineurioma, 26 scars, 23 nodular fasciitis, 6 low-grade fibromyxoid sarcomas, 6 angioleiomyomas, 5 neurofibromas, 5 dermatofibrosarcoma protuberans, 3 low-grade myofibroblastic sarcomas, 3 synovial sarcomas, 3 inflammatory myofibroblastic tumors, 2 schwannomas, and 1 each of Gardner-associated fibroma, radiation-associated spindle cell sarcoma, sclerotic fibroma, dermatofibroma, and glomus tumor). LEF1 expression was not only seen in 33/35 (94%) of DF but also observed in 19/23 (82%) nodular fasciitis, 7/19 (37%) soft tissue perineurioma, 2/3 (66%) synovial sarcoma, and 6/26 (23%) scar, as well as in 1 radiation-associated spindle cell sarcoma. The sensitivity and specificity of LEF1 IHC for diagnosis of DF were 94% and 70%, respectively. By comparison, β-catenin offered similar sensitivity, 94%, but 88% specificity. Positivity for LEF1 and β-catenin in combination showed sensitivity of 89%, lower than the sensitivity of β-catenin alone (94%); however, the combination of both LEF1 and β-catenin improved specificity (96%) compared to the specificity of β-catenin alone (88%). Although LEF1 has imperfect specificity in isolation, this stain has diagnostic utility when used in combination with β-catenin. [ABSTRACT FROM AUTHOR]

Aims: Anastomosing haemangiomas are benign tumours with anastomosing vascular channels that may mimic angiosarcoma. While anastomosing haemangiomas have been described in diverse locations, particularly the abdominal/paraspinal region, data on anastomosing haemangiomas in the mediastinum remain limited. We report the clinicopathological, radiological and molecular characteristics of the largest single‐institutional series of mediastinal anastomosing haemangiomas. Methods and results: In our pathology archives in 2011–23, we reviewed all vascular lesions involving the mediastinum and identified seven anastomosing haemangiomas. Clinical information was abstracted from medical charts; available radiological imaging was reviewed. Targeted DNA‐based next‐generation sequencing (447 genes, including GNAQ and GNA11) was performed on five cases. The seven patients included five women and two men, with an age range of 55–77 (median = 72) years. Of the six tumours with available radiology, two each were in the prevascular, visceral and paravertebral mediastinum, with lobulated peripheral enhancement in all tumours examined with contrast enhancement. Six patients underwent tumour resection; one patient received proton radiotherapy. Microscopically, each tumour was solitary and characterised by anastomosing capillary‐sized vessels lined by hobnail endothelial cells. Fibrin microthrombi, hyaline globules and extramedullary haematopoiesis were common. In the five tumours analysed by next‐generation sequencing, GNAQ p.Q209P was identified in one tumour; no additional reportable alterations were identified in the remaining cases. No recurrence was noted in the four patients with available follow‐up of 3–58 (median = 9.5) months after resection. Conclusion: While mediastinal anastomosing haemangiomas can microscopically mimic angiosarcoma, awareness of this entity and radiological correlation may help to circumvent this diagnostic pitfall. [ABSTRACT FROM AUTHOR]

Pseudoendocrine sarcoma (PES) is a recently described neoplasm typically arising in paravertebral soft tissues. Histologically, PES resembles well-differentiated neuroendocrine tumors but lacks expression of epithelial/neuroendocrine markers, and most show aberrant nuclear β-catenin positivity. We describe the clinicopathological and molecular features and DNA methylation profile of one PES. A resected paraspinal soft tissue mass in a 52-year-old man showed a neuroendocrine-like neoplasm, negative for keratin, and synaptophysin and showing diffuse nuclear β-catenin expression. Targeted NGS confirmed a CTNNB1 (p.S37C) mutation. Whole genome methylation analysis showed no match to any methylation class in the central nervous system tumor (versions 11b6 and 12b6) or sarcoma classifier (calibrated scores of ≤0.3), but clustered together with a recently reported PES in which methylation analysis was also performed. He remained disease-free for 18 months after surgery, followed by chemoradiation. As more cases are examined, our findings suggest that PES may have a unique methylation profiling signature. [ABSTRACT FROM AUTHOR]

Primary bone tumours can pose diagnostic problems due to their overlapping radiologic and histologic features. Given the recent advancement in our understanding of the biology of bone tumours, multiple immunohistochemical and molecular markers have been devised to aid in their diagnosis. This review provides brief updates on select bone tumours, including chondrosarcomas, benign chondrogenic tumours, osteosarcomas, benign osteogenic tumours, fibroosseous lesions, vascular tumours, osteoclastic giant cell‐rich or cystic tumours, chordoma, adamantinoma, small round blue cell sarcomas, and others. We discuss their salient molecular features and novel immunohistochemical correlates, along with some tips to avoid common diagnostic pitfalls. [ABSTRACT FROM AUTHOR]

Background and objectives: Bone tumours are relatively rare and, as a consequence, treatment in a centre with expertise is required. Current treatment guidelines also recommend review by a specialised pathologist. Here we report on international consensus‐based datasets for the pathology reporting of biopsy and resection specimens of bone sarcomas. The datasets were produced under the auspices of the International Collaboration on Cancer Reporting (ICCR), a global alliance of major (inter‐)national pathology and cancer organisations. Methods and results: According to the ICCR's process for dataset development, an international expert panel consisting of pathologists, an oncologic orthopaedic surgeon, a medical oncologist, and a radiologist produced a set of core and noncore data items for biopsy and resection specimens based on a critical review and discussion of current evidence. All professionals involved were bone tumour experts affiliated with tertiary referral centres. Commentary was provided for each data item to explain the rationale for selecting it as a core or noncore element, its clinical relevance, and to highlight potential areas of disagreement or lack of evidence, in which case a consensus position was formulated. Following international public consultation, the documents were finalised and ratified, and the datasets, including a synoptic reporting guide, were published on the ICCR website. Conclusion: These first international datasets for bone sarcomas are intended to promote high‐quality, standardised pathology reporting. Their widespread adoption will improve the consistency of reporting, facilitate multidisciplinary communication, and enhance comparability of data, all of which will help to improve management of bone sarcoma patients. [ABSTRACT FROM AUTHOR]

Angiomyofibroblastoma (AMF), a rare benign vulvovaginal mesenchymal tumour, poses a diagnostic challenge due to histologic and immunohistochemical overlap with other vulvar mesenchymal tumours. Recently, MTG1‐CYP2E1 fusion transcripts were reported in 5/5 AMFs; no other genetic alterations have been described to date. Herein, we sought to investigate the frequency of the MTG1‐CYP2E1 fusion and the presence of other potential genetic alterations in a cohort of AMFs (n = 7, patient age range: 28–49 years). Tumours demonstrated classic morphologic features including alternating hypo/hypercellular areas, capillary channels surrounded by epithelioid/spindled tumour cells, and variable amounts of mature adipose tissue. reverse transcription‐polymerase chain reaction (RT‐PCR) for MTG1‐CYP2E1 fusion, performed in all seven cases, showed the fusion transcript in five of six cases (one case with technical failure). Two tumours, including the one lacking the fusion, were subjected to targeted next‐generation sequencing (104 genes) and a sarcoma fusion assay (28 genes); the fusion negative AMF also underwent RNA sequencing. No additional mutations, copy number alterations, or fusion genes were identified with the assays employed. We conclude that the majority of AMFs harbour recurrent MTG1‐CYP2E1 fusion transcripts and identification of this fusion may aid in the diagnosis. [ABSTRACT FROM AUTHOR]

The use of denosumab to treat giant cell tumors of bone (GCT) and other giant cell‐containing bone tumors has become more common. While the clinicopathologic features of denosumab‐treated giant cell tumors of bone have been well‐illustrated, descriptions of other denosumab‐treated bone tumors are very limited. Surgical pathology files of two institutions and consultation files from two authors were searched for denosumab‐treated aneurysmal bone cysts and denosumab‐treated osteoblastomas. Clinicopathologic features were reviewed and analyzed. We identified four patients with denosumab‐treated bone tumors other than GCT from our surgical pathology and consultation files, including two aneurysmal bone cysts and two osteoblastomas. All were treated with denosumab for 0.5‐7.0 (median 4.5) months. Radiologically, denosumab‐treated tumors showed decreased size with increased ossification and mineralization on CT and heterogeneous intermediate to hypointense signal on MRI. Histologically, denosumab‐treated aneurysmal bone cyst contained thin, elongated, curvilinear, and anastomosing strands of bone with empty lacunae, while denosumab‐treated osteoblastoma showed circumscribed nodules of woven bone lined by small osteoblasts. Denosumab‐treated aneurysmal bone cyst and osteoblastoma showed treatment‐related morphologic changes that can mimic other bone neoplasms. Their recognition requires correlation with the clinical history of denosumab use and radiologic findings. [ABSTRACT FROM AUTHOR]

Background: Local recurrence of microinvasive sarcoma or benign aggressive pathologies can be limb- and life-threatening. Although frozen pathology is reliable, tumor microinvasion can be subtle or missed, having an impact on surgical margins and postoperative radiation planning. The authors' service has begun to temporize the tumor bed after primary tumor excision with a wound vacuum-assisted closure (VAC) pending formal margin analysis, with coverage performed in the setting of final negative margins. Methods: This retrospective analysis included all patients managed at a tertiary referral cancer center with VAC temporization after soft tissue sarcoma or benign aggressive tumor excision from 1 January 2000 to 1 January 2019 and at least 2 years of oncologic follow-up evaluation. The primary outcome was local recurrence. The secondary outcomes were distant recurrence, unplanned return to the operating room for wound/infectious indications, thromboembolic events, and tumor-related deaths. Results: For 62 patients, VAC temporization was performed. The mean age of the patients was 62.2 ± 22.3 years (median 66.5 years; 95% confidence interval [CI] 61.7–72.5 years), and the mean age-adjusted Charlson Comorbidity Index was 5.3 ± 1.9. The most common tumor histology was myxofibrosarcoma (51.6%, 32/62). The mean volume was 124.8 ± 324.1 cm3, and 35.5% (22/62) of the cases were subfascial. Local recurrences occurred for 8.1% (5/62) of the patients. Three of these five patients had planned positive margins, and 17.7% (11/62) of the patients had an unplanned return to the operating room. No demographic or tumor factors were associated with unplanned surgery. Conclusions: The findings showed that VAC-temporized management of microinvasive sarcoma and benign aggressive pathologies yields favorable local recurrence and unplanned operating room rates suggestive of oncologic and technical safety. These findings will need validation in a future randomized controlled trial. [ABSTRACT FROM AUTHOR]

Aberrant methylation of genomic DNA has been reported in many cancers. Specific DNA methylation patterns have been shown to provide clinically useful prognostic information and define molecular disease subtypes with different response to therapy and long-term outcome. Osteosarcoma is an aggressive malignancy for which approximately half of tumors recur following standard combined surgical resection and chemotherapy. No accepted prognostic factor save tumor necrosis in response to adjuvant therapy currently exists, and traditional genomic studies have thus far failed to identify meaningful clinical associations. We studied the genome-wide methylation state of primary tumors and tested how they predict patient outcomes. We discovered relative genomic hypomethylation to be strongly predictive of response to standard chemotherapy. Recurrence and survival were also associated with genomic methylation, but through more site-specific patterns. Furthermore, the methylation patterns were reproducible in three small independent clinical datasets. Downstream transcriptional, in vitro, and pharmacogenomic analysis provides insight into the clinical translation of the methylation patterns. Our findings suggest the assessment of genomic methylation may represent a strategy for stratifying patients for the application of alternative therapies. Christopher Lietz et al. examined genome-wide methylation in patient cohorts of primary osteosarcoma. Their results suggest that genomic hypomethylation is predictive of response to standard chemotherapy, and provide further insight into clinical implications of methylation patterns. [ABSTRACT FROM AUTHOR]

Background: Benign tumors of the hand present in a wide array of histological subtypes and compose most of the bony tissue tumors in the hand. This study evaluates the characteristics and treatment of benign bone tumors in light of one institution's experience. Methods: Histologically confirmed benign tumors of the hand were retrospectively identified using International Classification of Diseases codes from 1992 to 2015. A medical chart review was conducted to collect patient characteristics and tumor epidemiology and treatment. Results: A total of 155 benign bone tumors were identified. The median age of patients at the time of surgery was 39.9 ± 12.8 years. All bone tumors were located in the digits, and most were treated by intralesional curettage (n = 118, 76%). Pathologic fractures occurred in 79 bone tumors (51%). Conclusion: Enchondromas (n = 118, 76%) were the most common bone tumor in this series, whereas giant cell tumors were the most destructive and also had the highest recurrence rate (40%). Awareness of tumor features may help physicians with diagnosis, and awareness of recurrence rates is important when counseling patients. [ABSTRACT FROM AUTHOR]

Background: Histiocytic and dendritic cell neoplasms are a diverse group of tumors arising from monocytic or dendritic cell lineage. Whereas the genomic features for Langerhans cell histiocytosis and Erdheim‐Chester disease have been well described, other less common and often aggressive tumors in this broad category remain poorly characterized, and comparison studies across the World Health Organization diagnostic categories are lacking. Methods: Tumor samples from a total of 102 patient cases within four major subtypes of malignant histiocytic and dendritic cell neoplasms, including 44 follicular dendritic cell sarcomas (FDCSs), 41 histiocytic sarcomas (HSs), 7 interdigitating dendritic cell sarcomas (IDCSs), and 10 Langerhans cell sarcomas (LCSs), underwent hybridization capture with analysis of up to 406 cancer‐related genes. Results: Among the entire cohort of 102 patients, CDKN2A mutations were most frequent across subtypes and made up 32% of cases, followed by TP53 mutations (22%). Mitogen‐activated protein kinase (MAPK) pathway mutations were present and enriched among the malignant histiocytosis (M) group (HS, IDCS, and LCS) but absent in FDCS (72% vs. 0%; p <.0001). In contrast, NF‐κB pathway mutations were frequent in FDCSs but rare in M group histiocytoses (61% vs. 12%; p <.0001). Tumor mutational burden was significantly higher in M group histiocytoses as compared with FDCSs (median 4.0/Mb vs. 2.4/Mb; p =.012). We also describe a pediatric patient with recurrent secondary histiocytic sarcoma treated with targeted therapy and interrogated by molecular analysis to identify mechanisms of therapeutic resistance. Conclusion: A total of 42 patient tumors (41%) harbored pathogenic mutations that were potentially targetable by approved and/or investigative therapies. Our findings highlight the potential value of molecular testing to enable precise tumor classification, identify candidate oncogenic drivers, and define personalized therapeutic options for patients with these aggressive tumors. Implications for Practice: This study presents comprehensive genomic profiling results on 102 patient cases within four major subtypes of malignant histiocytic and dendritic cell neoplasms, including 44 follicular dendritic cell sarcomas (FDCSs), 41 histiocytic sarcomas (HSs), 7 interdigitating dendritic cell sarcomas (IDCSs), and 10 Langerhans cell sarcomas (LCSs). MAPK pathway mutations were present and enriched among the malignant histiocytosis (M) group (HS, IDCS, and LCS) but absent in FDCSs. In contrast, NF‐κB pathway mutations were frequent in FDCSs but rare in M group histiocytosis. A total of 42 patient tumors (41%) harbored pathogenic mutations that were potentially targetable by approved and/or investigative therapies. Histiocytic and dendritic cell neoplasms are a diverse group of tumors arising from the monocytic or dendritic cell lineage. This article presents the molecular characteristics of the four major subtypes of malignant histiocytic and dendritic cell neoplasms, focusing on genomic alterations that could represent therapeutic targets. [ABSTRACT FROM AUTHOR]

Background: There are no effective systemic therapies for chordoma. The recent successes of immunotherapeutic strategies in other cancers have resulted in a resurgence of interest in using immunotherapy in chordoma. These approaches rely on a functional interaction between the host's immune system and the expression of tumor peptides via the human leukocyte antigen (HLA) Class I antigen. It is not known whether chordoma cells express the HLA Class I antigen.Questions/purposes: (1) Do chordoma tumors exhibit defects in HLA Class I antigen expression? (2) What is the pattern of lymphocyte infiltration in chordoma tumors?Methods: Patients with chordoma treated at Massachusetts General Hospital between 1989 and 2009 were identified with permission from the institutional review board. Of the 75 patients who were identified, 24 human chordoma tumors were selected from 24 distinct patients based on tissue availability. Histology slides from these 24 formalin-fixed paraffin-embedded chordoma tissue samples were deparaffinized using xylene and ethanol and underwent heat-induced antigen retrieval in a citrate buffer. Samples were incubated with monoclonal antibodies directed against HLA Class I antigen processing machinery components. Antibody binding was detected via immunohistochemical staining. Staining intensity (negative, weakly positive, strongly positive) was assessed semiquantitatively and the percentage of chordoma cells stained for HLA Class I antigen subunits was assessed quantitatively. Hematoxylin and eosin-stained histology slides from the same 24 chordoma samples were assessed qualitatively for the presence of tumor-infiltrating lymphocytes and histologic location of these lymphocytes. Immunohistochemical staining with monoclonal antibodies directed against CD4 and CD8 was performed in a quantitative manner to identify the lymphocyte subtype present in chordoma tumors. All results were scored independently by two investigators and were confirmed by a senior bone and soft tissue pathologist.Results: Seven of 24 chordoma samples exhibited no staining by the anti-HLA-A heavy chain monoclonal antibody HC-A2, two had weak staining intensity, and eight had a heterogeneous staining pattern, with fewer than 60% of chordoma cells exhibiting positive staining results. Four of 24 samples tested were not stained by the anti-HLA-B/C heavy chain monoclonal antibody HC-10, five had weak staining intensity, and 11 displayed a heterogeneous staining pattern. For the anti-β-2-microglobulin monoclonal antibody NAMB-1, staining was detected in all samples, but 11 had weak staining intensity and four displayed a heterogeneous staining pattern. Twenty-one of 24 samples tested had decreased expression in at least one subunit of HLA Class I antigens. No tumors were negative for all three subunits. Lymphocytic infiltration was found in 21 of 24 samples. Lymphocytes were primarily found in the fibrous septae between chordoma lobules but also within the tumor lobules and within the fibrous septae and tumor lobules. Twenty-one of 24 tumors had CD4+ T cells and 11 had CD8+ T cells.Conclusion: In chordoma tissue samples, HLA Class I antigen defects commonly were present, suggesting a mechanism for escape from host immunosurveillance. Additionally, nearly half of the tested samples had cytotoxic CD8+ T cells present in chordoma tumors, suggesting that the host may be capable of mounting an immune response against chordoma tumors. The resulting selective pressure imposed on chordoma tumors may lead to the outgrowth of chordoma cell subpopulations that can evade the host's immune system.Clinical Relevance: These findings have implications in the design of immunotherapeutic strategies for chordoma treatment. T cell recognition of tumor cells requires HLA Class I antigen expression on the targeted tumor cells. Defects in HLA Class I expression may play a role in the clinical course of chordoma and may account for the limited or lack of efficacy of T cell-based immunity triggered by vaccines and/or checkpoint inhibitors. [ABSTRACT FROM AUTHOR]

Objectives: Coronavirus disease 19 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is associated with diverse clinical, including hematologic, abnormalities. We describe peripheral blood and bone marrow findings in deceased and living patients with COVID-19.Methods: We examined bone marrows from 20 autopsies and 2 living patients with COVID-19 using H&E-stained slides and immunohistochemical stains. Clinical history and laboratory values were reviewed. HScore was calculated to estimate risk of hemophagocytic lymphohistocytosis (HLH).Results: The deceased patients included 12 men and 8 women (aged 32 to >89 years; median, 63 years). Hematologic abnormalities included frequent neutrophilic leukocytosis, lymphopenia, anemia, and thrombocytopenia; one patient showed striking erythrocytosis. The bone marrows were all normocellular to hypercellular, most showing maturing trilineage hematopoiesis with myeloid left shift. In all 19 evaluable bone marrows, hemophagocytic histiocytes were identified. The HScore for secondary HLH ranged from 35 to 269 (median, 125; >169 in 5 patients). Coinfections were identified in 6 patients. In 2 living patients, bone marrow showed maturing trilineage hematopoiesis, including one showing few hemophagocytic histiocytes.Conclusions: Peripheral blood from deceased patients with COVID-19 frequently showed neutrophilic leukocytosis, lymphopenia, and, rarely, secondary polycythemia; hemophagocytosis was common in their bone marrow. Consistent with other studies, we provide histopathologic evidence of secondary HLH development in patients with COVID-19. [ABSTRACT FROM AUTHOR]

Aims: Simple bone cysts are benign intramedullary tumours primarily involving the long bones in skeletally immature individuals. Several mechanisms have been proposed for their pathogenesis. Although the diagnosis is typically straightforward, the interpretation can be problematic, because of superimposed fracture causing them to resemble aneurysmal bone cysts and other tumours. EWSR1–NFATC2 or FUS–NFATC2 fusions, which are characteristic of a subset of aggressive round cell sarcomas, have been recently detected in simple bone cysts. The aim of this study was to examine the clinicopathological and molecular features in a series of simple bone cysts. Methods and results: Using RNA‐based next‐generation sequencing and/or fluorescence in‐situ hybridisation, we investigated the presence of EWSR1 or FUS rearrangements in nine simple bone cysts. The patients were five females and four males, aged 3–23 years (median, 14 years); the tumours ranged from 19 mm to 160 mm (median, 46 mm) in size, and involved the femur (n = 3), humerus (n = 2), fibula (n = 2), tibia (n = 1), and iliac wing (n =1). We identified three cases with EWSR1–NFATC2 fusion (showing identical breakpoints to those in EWSR1–NFATC2 sarcomas) and one additional case with FUS rearrangement. Unlike in EWSR1–NFATC2 sarcomas, immunohistochemical expression of NKX3.1 and NKX2.2 was absent in two simple bone cysts tested. Conclusions: More than 40% of simple bone cysts harbour genetic alterations confirming that they are neoplastic, investigation of EWSR1 and/or FUS rearrangement may help to distinguish simple bone cysts from mimics, and NFATC2 rearrangement is not pathognomonic of malignancy. [ABSTRACT FROM AUTHOR]

Aims: Nuclear protein in testis (NUT) carcinoma, an aggressive tumour driven by NUTM1 rearrangements, often involves the lung/mediastinum and shows squamous differentiation. We encountered an index patient with a thoracic NUT carcinoma diagnosed by molecular testing, showing extensive pleural involvement and diffuse thyroid transcription factor‐1 (TTF‐1) expression, initially suggestive of lung adenocarcinoma with pseudomesotheliomatous growth. We thus gathered an institutional series of thoracic NUT carcinomas to examine their pathological spectrum. Methods and results: We searched for thoracic NUT carcinomas in our surgical pathology files and in 2289 consecutive patients with primary thoracic tumours investigated with RNA‐based assays. We performed NUT immunohistochemistry on 425 additional lung adenocarcinomas. Collectively, we identified six patients (five men and one woman; age 31–80 years; four never‐smokers) with thoracic NUT carcinomas confirmed by molecular testing (including five with positive NUT immunohistochemistry). They died at 2.3–12.9 months (median, 2.8 months) after presentation. Two patients were diagnosed by histopathological assessment, and the remaining four (including the index patient) were diagnosed by molecular testing. Analysis of the index case revealed expression of multiple neuroendocrine markers and TTF‐1; no ultrastructural evidence of neuroendocrine differentiation was noted. No additional NUT‐positive cases were found by immunohistochemical screening. Conclusions: Although NUT carcinoma classically shows squamous differentiation, it can rarely express TTF‐1 (even diffusely) and/or multiple neuroendocrine markers. This immunophenotypic spectrum may lead to diagnostic confusion with pulmonary adenocarcinoma, neuroendocrine tumour, and others. To circumvent this pitfall, NUT immunohistochemistry and/or NUTM1 molecular testing should be considered in primitive‐appearing tumours, regardless of their immunophenotypic features. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study was to characterize chondrosarcoma tumor infiltration by immune cells and the expression of immunologically relevant molecules. This information may contribute to our understanding of the role of immunological events in the pathogenesis of chondrosarcoma and to the rational design of immunotherapeutic strategies. Patients and Methods: A tissue microarray (TMA) containing 52 conventional and 24 dedifferentiated chondrosarcoma specimens was analyzed by immunohistochemical staining for the expression of parameters associated with tumor antigen-specific immune responses, namely, CD4+ and CD8+ tumor infiltrating lymphocytes (TILs) and the expression of HLA class I heavy chain, beta-2 microglobulin (β2m), HLA class II and immune checkpoint molecules, B7-H3 and PD-1/PD-L1. The results were correlated with histopathological characteristics and the clinical course of the disease. Results: CD8+ TILs were present in 21% of the conventional and 90% of the dedifferentiated chondrosarcoma tumors tested. B7-H3 was expressed in 69% of the conventional and 96% of the dedifferentiated chondrosarcoma tumors tested. PD-1 and PD-L1 were expressed 53% and 33% respectively of the dedifferentiated tumors tested. PD-L1 expression was associated with shorter time to metastasis. Conclusion: The tumor infiltration by lymphocytes suggests that chondrosarcoma is immunogenic. Defects in HLA class I antigen and expression of the checkpoint molecules B7-H3 and PD-1/PD-L1 suggest that tumor cells utilize escape mechanisms to avoid immune recognition and destruction. This data implies that chondrosarcoma will benefit from strategies that enhance the immunogenicity of tumor antigens and/or counteract the escape mechanisms. [ABSTRACT FROM AUTHOR]

Cancer is driven by genetic change, and the advent of massively parallel sequencing has enabled systematic documentation of this variation at the whole-genome scale1–3. Here we report the integrative analysis of 2,658 whole-cancer genomes and their matching normal tissues across 38 tumour types from the Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium of the International Cancer Genome Consortium (ICGC) and The Cancer Genome Atlas (TCGA). We describe the generation of the PCAWG resource, facilitated by international data sharing using compute clouds. On average, cancer genomes contained 4–5 driver mutations when combining coding and non-coding genomic elements; however, in around 5% of cases no drivers were identified, suggesting that cancer driver discovery is not yet complete. Chromothripsis, in which many clustered structural variants arise in a single catastrophic event, is frequently an early event in tumour evolution; in acral melanoma, for example, these events precede most somatic point mutations and affect several cancer-associated genes simultaneously. Cancers with abnormal telomere maintenance often originate from tissues with low replicative activity and show several mechanisms of preventing telomere attrition to critical levels. Common and rare germline variants affect patterns of somatic mutation, including point mutations, structural variants and somatic retrotransposition. A collection of papers from the PCAWG Consortium describes non-coding mutations that drive cancer beyond those in the TERT promoter4; identifies new signatures of mutational processes that cause base substitutions, small insertions and deletions and structural variation5,6; analyses timings and patterns of tumour evolution7; describes the diverse transcriptional consequences of somatic mutation on splicing, expression levels, fusion genes and promoter activity8,9; and evaluates a range of more-specialized features of cancer genomes8,10–18.The flagship paper of the ICGC/TCGA Pan-Cancer Analysis of Whole Genomes Consortium describes the generation of the integrative analyses of 2,658 cancer whole genomes and their matching normal tissues across 38 tumour types, the structures for international data sharing and standardized analyses, and the main scientific findings from across the consortium studies. [ABSTRACT FROM AUTHOR]

Primary intraosseous myoepithelial tumors are rare neoplasms with only a handful of cases described in the medical literature. To date, intraosseous variant of benign myoepithelioma, due to its rarity, has not been studied ultrastructurally, and only one case of a malignant intraosseous myoepithelioma has been described. Three cases were retrieved from the files at the Massachusetts General Hospital (MGH). A diagnosis of benign myoepithelioma was made in case 1 and malignant epithelioma in cases 2 and 3. Ultrastructurally, intermediate filaments (without dense bodies) were found in each case with an abundance in case 1 and lesser amounts in cases 2 and 3. Surprisingly, cell junctions were not identified in case 1. However, they were found occasionally as intermediate junctions in case 2 and were easily identified as desmosome like junctions in case 3. The nucleus was irregular in the neoplastic cells of benign myoepithelioma which contrasted with cases 2 and 3 where the nuclei were oval yet had visible nucleoli. Herein, we add three new cases, including two new cases of malignant myoepithelioma. We also provide the first ultrastructural description of benign myoepithelioma of bone. [ABSTRACT FROM AUTHOR]

Background: MicroRNAs are small, noncoding RNAs that regulate the expression of posttranslational genes. The presence of some specific microRNAs has been associated with increased risk of both local recurrence and metastasis and worse survival in patients with osteosarcoma. Pathologic fractures in osteosarcoma are considered to be more the manifestation of a neoplasm with a more aggressive biological behavior than the cause itself of worse prognosis. However, this has not been proved at the biological or molecular level. Currently, there has not been a microRNA profiling study of patients who have osteosarcoma with and without pathologic fractures that has described differences in terms of microRNA profiling between these two groups and their correlation with biologic behavior.Questions/purposes: (1) In patients with osteosarcoma of the extremities, how do the microRNA profiles of those with and without pathologic fractures compare? (2) What relationship do microRNAs have with local recurrence, risk of metastasis, disease-specific survival, and overall survival in osteosarcoma patients with pathologic fractures?Methods: Between 1994 and 2013, 217 patients were diagnosed and treated at our institution for osteosarcoma of the extremities. Patients were excluded if (1) they underwent oncologic resection of the osteosarcoma at an outside institution (two patients) or (2) they were diagnosed with an extraskeletal osteosarcoma (29 patients) or (3) they had less than 1 year of clinical follow-up and no oncologic outcome (local recurrence, metastasis, or death) (four patients). A total of 182 patients were eligible. Of those, 143 were high-grade osteosarcomas. After evaluation of tumor samples before chemotherapy treatment, a total of 80 consecutive samples were selected for sequencing. Demographic and clinical comparison between the sequenced and non-sequenced patients did not demonstrate any differences, confirming that both groups were comparable. Diagnostic samples from the extremities of 80 patients with high-grade extremity osteosarcomas who had not yet received chemotherapy underwent microRNA sequencing for an ongoing large-scale osteosarcoma genome profiling project at our institution. Six samples were removed after a second look by a musculoskeletal pathologist who verified cellularity and quality of samples to be sequenced, leaving a total of 74 patients. Of these, two samples were removed as they were confirmed to be pelvic tumors in a second check after sequencing. The final study sample was 72 patients (11 patients with pathologic fractures and 61 without). Sequencing data were correlated with fractures and local recurrence, risk of metastasis, disease-specific survival, and overall survival through Kaplan-Meier analyses.Results: Several microRNAs were expressed differently between the two groups. Among the markers with the highest differential expression (edgeR and DESeq algorithms), Hsa-mIR 656-3p, hsa-miR 493-5p, and hsa-miR 381-3p were upregulated in patients with pathologic fractures, whereas hsa-miR 363, hsa-miR 885-5p, and has-miR 20b-5p were downregulated. The highest differential expression fracture and nonfracture-associated microRNA markers also distinguished groups of patients with different metastasis risk, a well as different disease-specific and overall survival. Furthermore, the profile of pathologic fractures demonstrated a higher differential expression for microRNA markers that were previously associated with a higher risk of metastasis and lower survival rates in patients with osteosarcoma.Conclusions: In patients who have osteosarcoma, the microRNA profiles of those with pathologic fractures are different than of patients without pathologic fractures. The highest differential expression mircroRNA molecules in patients with pathologic fractures predict also higher risk of metastatic disease as well as worse disease-specific survival and overall survival. Furthermore, we found higher differential expression of microRNAs in the pathologic fracture group previously associated with poor prognosis. The higher risk of metastasis and poorer overall survival in patients with pathologic fractures is inherent to tumor aggressive biologic behavior. It is plausible that the fracture itself is not the direct cause of worse prognosis but another manifestation of tumor biologic aggressiveness. Identification of these molecules through liquid biopsies may help to determine which patients may benefit from surgery before fractures occur. The same technology can be applied to identify patterns of response to conventional chemotherapy, assisting in more specific and accurate systemic therapy.Level Of Evidence Level: III, prognostic study. [ABSTRACT FROM AUTHOR]

Conventional well-differentiated, dedifferentiated, and myxoid liposarcomas have long been known to harbor numerous typical genetic alterations that allow for diagnosis of these tumors. These include MDM2 and CDK4 amplification in well-differentiated and dedifferentiated liposarcomas as well as FUS-DDIT3 rearrangements in myxoid liposarcoma. More recently, in-frame TRIO-TERT fusion genes have been described in a subset of non-translocation-related sarcomas including myxofibrosarcoma, dedifferentiated liposarcoma, undifferentiated pleomorphic sarcoma, pleomorphic rhabdomyosarcoma, and leiomyosarcoma. These genetic rearrangements lead to TERT mRNA expression levels hundreds of times higher than normal, causing increased telomerase activation in these tumors. Herein, we describe an unusual case of a liposarcoma with spindle cell features and a TRIO-TERT fusion transcript identified through next-generation sequencing. [ABSTRACT FROM AUTHOR]

Chemical cross‐linking of ultrahigh molecular weight polyethylene (UHMWPE) using an organic peroxide followed by high temperature melting results in a large increase in toughness accompanied by a decrease in cross‐link density, which, surprisingly does not compromise the wear resistance. We compared the mechanical properties and wear behavior of a vitamin E blended, chemically cross‐linked and high temperature melted UHMWPE produced by ram extrusion (PRX HTM) to those measured with the clinically available 100‐kGy irradiated and melted UHMWPE (CISM 100). We also assessed the local biocompatibility of PRX‐HTM in rabbit subcutaneous pouch and osteochondral defect models. The ultimate tensile strength and pin‐on‐disc wear rate were similar to CISM 100; whereas the elongation‐at‐break and impact toughness were much higher with PRX‐HTM. The stress intensity factor range at crack inception was also higher with PRX‐HTM. Accelerated aging did not result in any measurable oxidation or changes in mechanical properties. Hip simulator wear rate of acetabular liners made with PRX‐HTM was 0.3 ± 0.4 mg/million‐cycle, similar to that reported for CISM 100 liners. The wear particles were largely spherical with a number‐averaged particle size of 0.95 μm with ~75% of particles below 1 μm. The subcutaneous and osteochondral rabbit implantations showed no histological differences between PRX‐HTM and the control CISM 100. Pre‐clinical wear, mechanical, and biocompatibility testing of PRX HTM showed feasibility for the use of this material as a total joint arthroplasty implant bearing surface. This process has the potential of eliminating the additional step of radiation cross‐linking by combining consolidation and cross‐linking while improving toughness. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1945–1952, 2019. [ABSTRACT FROM AUTHOR]

Perivascular epithelioid cell tumors (PEComas) are rare mesenchymal neoplasms composed of perivascular epithelioid cells that are immunoreactive for both melanocytic and myogenic markers. Recently, a fibroma-like PEComa associated with tuberous sclerosis complex (TSC) has been identified. We describe the first intra-articular case of a fibroma-like PEComa in a 44-year-old man who presented with a hypointense intra-articular knee mass, which was mistaken for tenosynovial giant cell tumor, diffuse type. This case report demonstrates that fibroma-like PEComa should be included in the extended differential diagnosis of intra-articular soft tissue masses. In addition, given their strong association with TSC mutations, a diagnosis of fibroma-like PEComa should trigger an evaluation for TSC. [ABSTRACT FROM AUTHOR]

Background and purpose Sacral intraosseous schwannomas represent a rare subset of schwannomas. The existing literature detailing the radiographic appearance of intraosseous schwannomas is limited. The aim of this study is to formally characterize the radiological appearance of sacral intraosseous schwannomas to differentiate them from other lytic lesions. Materials and methods Imaging studies of 13 pathologically proven intraosseous schwannomas were reviewed from multiple institutions by fellowship-trained radiologists. A PubMed search was performed and identified four papers pertaining to the imaging characteristics of sacral intraosseous schwannomas. The results of these papers were compared to findings from our cases. Results All tumors had heterogeneous signals and were predominately solid but cystic components with fluid-fluid levels were present. The tumors caused a mass effect but none infiltrated the surrounding soft tissues. Post-contrast T1-weighted images revealed heterogeneous enhancement in all 13 tumors and four possessed non-enhancing cysts. A literature review identified 16 other cases of sacral intraosseous schwannomas forming a total of 29 cases examined. Conclusions Sacral intraosseous schwannomas should be considered in the differential diagnosis for both radiologists and pathologists when dealing with large expansile, lytic lesions, with well-defined sclerotic margins involving the sacrum. This is particularly important in middle-aged adults presenting with pathology centered around S2-3. [ABSTRACT FROM AUTHOR]

BACKGROUND: Diagnosing giant cell‐rich bone tumors can be challenging on limited biopsies. H3 histone family member 3A (H3F3A) (G34W/V/R/L) mutations are present in the majority of giant cell tumors (GCTs) of bone and H3 histone family member 3B (H3F3B) (K36M) mutations are present in nearly all chondroblastomas, but are absent in histologic mimics. Mutation‐specific immunohistochemistry (IHC) is highly specific for GCT and chondroblastoma in surgical excisions. The objective of the current study was to validate H3G34W and H3K36M IHC in the diagnosis of giant cell‐rich bone tumors on fine‐needle aspiration and core needle biopsy specimens. METHODS: IHC was performed using monoclonal antibodies against histone H3.3 G34W and K36M in GCTs of bone (26 cases, including 2 malignant cases), GCT of Paget disease (1 case), chondroblastoma (8 cases), aneurysmal bone cyst (7 cases), and osteosarcoma (13 cases) with available fine‐needle aspiration and/or core needle biopsy specimens from 2 institutions. H3F3A and H3F3B Sanger sequencing was performed on all 4 H3G34W IHC‐negative GCTs. RESULTS: IHC for H3G34W was positive in 22 of 26 GCTs (85%) and negative in all histologic mimics. IHC for H3K36M was positive in all 8 chondroblastomas and negative in all histologic mimics. IHC results were concordant between biopsy and surgical specimens in 152 of 158 samples (96%). Sequencing identified alternate H3F3A G34L and G34V mutations in 1 IHC‐negative GCT each, but no mutation was found in the remaining 2 cases. CONCLUSIONS: H3G34W and H3K36M IHC is highly specific for GCT and chondroblastoma, respectively, among giant cell‐rich bone tumors, and is useful for confirming the diagnosis in limited biopsies. The presence of alternate H3F3A mutations accounts for the H3G34W IHC negativity in a subset of GCT of bone cases. Cancer Cytopathol 2018. © 2018 American Cancer Society. [ABSTRACT FROM AUTHOR]

Aims: Cystic lesions derived from the synovial and ligamentous structures of the spine have varied histological appearances. Not uncommonly, there is discrepancy between the clinicoradiological diagnosis and histology. Therefore, we sought to characterise the histological features of tissue submitted as ‘synovial cysts’ of the spine. Methods and results: Resected specimens of the spine labelled ‘synovial cysts’ and ‘lumbar cysts’ were histologically evaluated and classified on the basis of histopathological features. Seventy‐five histological samples of spinal cysts were identified. Thirty‐one were classified as synovial cysts (definite synovial lining), 28 showed pseudocystic degeneration of the ligamentum flavum, seven showed pseudocyst formation without evidence of a synovial lining or degeneration of the ligamentum flavum, and eight showed cyst contents only or no histological evidence of cyst wall for evaluation. Twenty‐five cases (33%), especially those showing pseudocystic degeneration of the ligamentum flavum, were associated with very characteristic tumour calcinosis‐like calcium deposition with a surrounding foreign‐body giant‐cell reaction. Conclusion: Histology of ‘synovial cysts’ of the spine shows varied types of cyst; a large proportion are not synovial‐lined cysts, but rather show pseudocystic degenerative changes of the ligamentum flavum, often associated with very characteristic finely granular calcifications and a foreign‐body giant‐cell reaction. This may have implications not only for understanding the pathogenesis of these lesions, but also for their varied responses to non‐surgical interventions. [ABSTRACT FROM AUTHOR]

Objective: To assess the radiographic and clinicopathologic features of synovial sarcoma of the nerve that were clinically or radiologically interpreted as benign peripheral nerve sheath tumor.Materials and Methods: Five patients with synovial sarcoma arising from the peripheral nerve and interpreted clinically and radiologically as peripheral nerve sheath tumors were identified. Clinicopathologic and imaging features were evaluated.Results: There were three females and two males, ranging in age from 28 to 50 (mean 35.8) years. Most patients (4/5) complained of a mass, discomfort or pain. MR images demonstrated a heterogeneous, enhancing, soft tissue mass contiguous with the neurovascular bundle. On histologic examination, most tumors were monophasic synovial sarcoma (4/5). At the time of surgery, all tumors were noted to arise along or within a peripheral nerve. All patients were alive with no evidence of disease with median follow-up of 44 (range 32-237) months. For comparison, approximately 775 benign peripheral nerve sheath tumors of the extremities were identified during the same time period.Conclusions: Primary synovial sarcoma of the nerve can mimic peripheral nerve sheath tumors clinically and on imaging and should be included in the differential diagnosis for tumors arising from peripheral nerves. [ABSTRACT FROM AUTHOR]