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Introduction: The percentage of tumor necrosis is a crucial prognostic factor in osteosarcoma. Many studies adopt a 90 % cutoff based on osteoblastic osteosarcoma, but these findings are generalized to all conventional subtypes, including chondroblastic osteosarcoma. We sought to answer these questions: (1) Is tumor necrosis ≥90 % associated with better overall survival (OS) and disease-free survival (DFS) in osteoblastic and chondroblastic osteosarcoma? (2) Does the osteosarcoma subtype impact tumor necrosis? (3) Does the osteosarcoma subtype in "good" responders (tumor necrosis ≥90 %) affect OS and DFS?., Materials and Methods: We conducted a retrospective study of 156 patients with osteoblastic and chondroblastic osteosarcoma treated at our institution. All patients received a standardized chemotherapy protocol and underwent surgery with the goal of achieving negative margins (R0 resection). Propensity-score matching was performed to adjust for potential confounders. Kaplan-Meier survival analysis and Cox proportional hazards modeling were performed., Results: Patients with osteoblastic osteosarcoma and tumor necrosis ≥90 % had higher 5- and 10-year OS and DFS compared to those with necrosis <90 %. In chondroblastic osteosarcoma, a trend towards higher OS and DFS was seen in patients with tumor necrosis ≥90 %; this, however, was not significant. Chondroblastic osteosarcoma was not a risk factor for either tumor necrosis <90 % (p = 0.89) or tumor necrosis <70 % (p = 0.57). Patients with osteoblastic or chondroblastic osteosarcoma that were deemed "good" responders (tumor necrosis ≥90 %) had similar OS and DFS at the 5- and 10-year marks., Conclusion: Conventional osteosarcoma subtype was not a risk factor for "poor" response. Survival outcomes (OS and DFS) were similar for osteoblastic and chondroblastic osteosarcoma with good response to chemotherapy., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

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., (© 2022 John Wiley & Sons Ltd.)

Dedifferentiated chondrosarcoma is rare, aggressive, and microscopically bimorphic. How pathologic features such as the amounts of dedifferentiation affect prognosis remains unclear. We evaluated the percentages and sizes of dedifferentiation in a consecutive institutional series of dedifferentiated chondrosarcomas from 1999 to 2021. The statistical analysis included cox proportional hazard models and log-rank tests. Of the 67 patients (26 women, 41 men; age, 39 to >89 [median 61] years; 2 with Ollier disease), 58 presented de novo; 9 were identified with conventional chondrosarcomas 0.6-13.2 years (median, 5.5 years) prior. Pathologic fracture and distant metastases were noted in 27 and 7 patients at presentation. The tumors involved the femur (n = 27), pelvis (n = 22), humerus (n = 7), tibia (n = 4), scapula/ribs (n = 4), spine (n = 2), and clivus (n = 1). In the 56 resections, the tumors ranged in size from 3.5 to 46.0 cm (median, 11.5 cm) and contained 1%-99.5% (median, 70%) dedifferentiated components that ranged in size from 0.6 to 24.0 cm (median, 7.3 cm). No correlation was noted between total size and percentage of dedifferentiation. The dedifferentiated components were typically fibrosarcomatous or osteosarcomatous, whereas the associated cartilaginous components were predominantly grade 1-2, rarely enchondromas or grade 3. The entire cohort's median overall survival and progression-free survival were 11.8 and 5.4 months, respectively. In the resected cohort, although the total size was not prognostic, the percentage of dedifferentiation ≥20% and size of dedifferentiation >3.0 cm each predicted worse overall survival (9.9 vs 72.5 months; HR, 3.76; 95% CI, 1.27-11.14; P = .02; 8.7 vs 58.9 months; HR, 3.03; 95% CI, 1.21-7.57; P = .02, respectively) and progression-free survival (5.3 vs 62.1 months; HR, 3.05; 95% CI, 1.13-8.28; P = .03; 5.3 vs 56.6 months; HR, 2.50; 95% CI, 1.06-5.88; P = .04, respectively). In conclusion, both the percentages and sizes of dedifferentiation were better prognostic predictors than total tumor sizes in dedifferentiated chondrosarcomas, highlighting the utility of their pathologic evaluations., (Copyright © 2022 United States & Canadian Academy of Pathology. Published by Elsevier Inc. All rights reserved.)

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., (© 2022 Scandinavian Societies for Medical Microbiology and Pathology.)

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., (© 2022. The Author(s).)

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.

Aneurysmal bone cyst is a benign bone neoplasm that most commonly arises from the metaphyses of long bones in the first and second decades of life. Here, we describe a case of an aneurysmal bone cyst that occurred in the distal tibial diaphysis of a 72-year-old female that was concerning for malignancy on imaging, demonstrating cortical breakthrough and soft tissue extension. Histologically, the tumor showed the characteristic morphologic features of aneurysmal bone cyst. Fluorescence in situ hybridization was positive for USP6 rearrangement, and RNA sequencing revealed a USP6 gene fusion with VDR, a novel partner that encodes the vitamin D receptor and that has not been implicated previously in human neoplasia. This case highlights the diagnostic challenges presented by aneurysmal bone cyst in elderly adults, and it expands the genetic spectrum of USP6 rearrangements., (© 2021 Wiley Periodicals LLC.)

Giant cell tumor of bone is a locally aggressive, rarely metastasizing neoplasm. Evidence suggests that the neoplastic cells may be osteoblastic in differentiation. Standard treatment is surgical removal, but medical therapy with denosumab, an inhibitor of receptor activator of nuclear factor-κβ ligand, has become a component of patient management in select cases. Denosumab-treated giant cell tumor of bone (DT-GCTB) shows drastic morphologic changes including the presence of abundant bone. To further determine the relationship of the neoplastic cells to osteoblast phenotype, we performed a morphologic and immunohistochemical study on a series of DT-GCTB. Cases of DT-GCTB were retrieved from surgical pathology files, available slides were reviewed, and immunohistochemistry for H3.3 G34W, SATB2, and p63 was performed. The cohort included 31 tumors from 30 patients (2:3 male:female), ages 15 to 73 years (median=36 y). The morphology of post-denosumab-treated tumors ranged from tumors composed of an abundant bone matrix with few spindle cells to spindle cell-predominant tumors. Five had focal residual classic CGTB, and 2 manifested mild nuclear atypia. The majority expressed all markers: 86.2% for H3.3 G34W, 96.7% for SATB2, and 100% for p63. All markers stained the various tumor components including spindle cells and the cells on the surface of and within the treated tumor bone matrix. Most markers were also positive in reactive-appearing woven bone adjacent to tumor: 84.6% for H3.3 G34W, 100% for SATB2, and 68% for p63. These findings suggest that denosumab treatment of giant cell tumor of bone results in osteoblastic differentiation with bone production.

Chondroblastoma is currently classified as a benign neoplasm; however, chondroblastoma and chondroblastoma-like osteosarcoma have morphologic overlap, raising the possibility that some tumors diagnosed as chondroblastoma-like osteosarcoma might actually represent malignant chondroblastoma. The H3F3B K36M point mutation, which has not been reported in osteosarcoma, is identified in 95% of chondroblastomas and is reliably detectable by immunohistochemistry (IHC). We reviewed 11 tumors diagnosed as atypical chondroblastoma, malignant chondroblastoma, or chondroblastoma-like osteosarcoma (median follow-up: 8.8 years; range: 4 months-26.4 years). Seven chondroblastomas with cytologic atypia and permeative growth were designated "malignant chondroblastoma"; six were H3K36M-positive by IHC. Relative to conventional chondroblastoma, malignant chondroblastoma occurred in older individuals (median: 52 years; range: 29-57 years) and arose at unusual sites. Three of four tumors with long-term follow-up recurred, and one patient died of widespread metastases. One was found to have chromosomal copy number alter4ations and a SETD2 mutation in addition to H3F3B K36M. The four remaining tumors were classified as chondroblastoma-like osteosarcoma. Chondroblastoma-like osteosarcoma occurred in younger patients (median: 21 years; range: 19-40 years) than malignant chondroblastoma. In contrast to malignant chondroblastoma, all had regions of malignant cells forming bone. Two of three patients with long-term follow-up developed recurrences, and two died of disease, one with widespread metastases. No mutations in H3F3A/H3F3B were detected by Sanger sequencing. While malignant chondroblastoma and chondroblastoma-like osteosarcoma show significant morphologic overlap, they have distinct clinical presentations and genetic findings. When considering this challenging differential diagnosis, IHC using histone H3 mutation-specific antibodies is a critical diagnostic adjunct.

Context.—: Cartilaginous tumors represent one of the most common tumors of bone. Management of these tumors includes observation, curettage, and surgical excision or resection, depending on their locations and whether they are benign or malignant. They can be diagnostically challenging, particularly in small biopsies. In rare cases, benign tumors may undergo malignant transformation., Objective.—: To review common cartilaginous tumors, including in patients with multiple hereditary exostosis, Ollier disease, and Maffucci syndrome, and to discuss problems in the interpretation of well-differentiated cartilaginous neoplasms of bone. Additionally, the concept of atypical cartilaginous tumor/chondrosarcoma grade 1 will be discussed and its use clarified., Data Sources.—: PubMed (US National Library of Medicine, Bethesda, Maryland) literature review, case review of archival cases at the Massachusetts General Hospital, and personal experience of the authors., Conclusions.—: This review has examined primary well-differentiated cartilaginous lesions of bone, including their differential diagnosis and approach to management. Because of the frequent overlap in histologic features, particularly between low-grade chondrosarcoma and enchondroma, evaluation of well-differentiated cartilaginous lesions should be undertaken in conjunction with thorough review of the imaging studies.

The entity "pericytoma with t(7;12)" was described as a rare, distinct perivascular myoid neoplasm provisionally classified within the family of myopericytic tumors that demonstrates t(7;12)(p22;q13) translocation with resultant ACTB-GLI1 fusion and biologically was felt to behave in an indolent fashion. However, a recent study showed that tumors with this and similar translocations may have variable morphology and immunohistochemical phenotype with inconsistent myopericytic characteristics and a propensity for metastasis, raising questions regarding the most appropriate classification of these neoplasms. Herein, we report 3 additional patients with tumors harboring t(7;12) and ACTB-GLI1 fusion. The tumors arose in adults and involved the proximal tibia and adjacent soft tissues, scapula and adjacent soft tissues, and ovary. All tumors were composed of round-to-ovoid cells with a richly vascularized stroma with many small, delicate, branching blood vessels, where the neoplastic cells were frequently arranged in a perivascular distribution. Both tumors involving bone showed histologic features of malignancy. By immunohistochemistry, all tested tumors were at least focally positive for smooth muscle actin (3/3) and CD99 (patchy) (2/2), with variable staining for muscle-specific actin (2/3), S100 protein (1/3), epithelial membrane antigen (2/3), and pan-keratin (1/3); all were negative for desmin and WT1 (0/3). The 2 patients with bone tumors developed metastases (27 and 84 mo after diagnosis). Whether these tumors are best classified as malignant myopericytoma variants or an emerging translocation-associated sarcoma of uncertain differentiation remains to be fully clarified; however, our study further documents the potential for these tumors to behave in an aggressive fashion, sometimes over a prolonged clinical course.

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.

The classification of bone neoplasms composed of small round cells is experiencing a transformation after the discovery of various gene fusion rearrangements that determine diagnosis, behavior, and response to therapy. We present herein 4 new cases of small round cell tumor of the bone that harbor NFATc2 rearrangements involving either EWSR1 or FUS genes. We studied the clinical presentation, pathologic features, genetics (FISH, targeted RNA sequencing) and outcome in these 4 patients. We also reviewed the literature describing similar cases. All our patients were male. The median age at diagnosis was 33.5 years. All tumors presented in long bones of the extremities as a large destructive mass with a mean size of 12.5 cm. All cases were hypercellular with prominent collagenous stroma and consisted of small to medium size round cells arranged in cords, thin trabeculae, and pseudoacinar structures. Most cases showed focal or diffuse membrane staining for CD99; whereas S100, synaptophysin and chromogranin were negative. EMA showed cytoplasmic staining in one case. Genetic studies identified EWSR1-NFATc2 fusion in 3 cases, and FUS-NFATc2 fusion in one case. Two patients were treated with neoadjuvant chemotherapy using Ewing sarcoma regimens, and surgical excision was performed on 3 patients; necrosis was minimal. Follow-up is limited; after a median follow-up of 8.7 months, one patient developed local recurrence and metastases to the lungs. Poorly differentiated round cell sarcoma with EWSR1/FUS-NFATc2 fusions are uncommon. The tumors have consistent clinical findings, morphology, and immunoprofile that in combination are distinctive and differ from that of Ewing sarcoma. Importantly, these tumors do not respond to Ewing sarcoma chemotherapy regimens., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Maxillofacial central giant cell lesions (CGCLs) are often locally aggressive tumors in young patients that may be histologically very similar to or quite distinct when compared with giant cell tumors (GCTs) of long bones. It has been well established that GCTs express high levels of receptor activator of nuclear factor-kappa B ligand (RANKL) and are amenable to treatment with denosumab. To assess the predictive value of morphology, we evaluated CGCLs with GCT-like or non-GCT-like histology for RANKL expression by RNA in situ hybridization. Tumors were classified by clinical and radiographic criteria as aggressive or nonaggressive and histopathologically as resembling GCT or non-GCT-like. RNA in situ hybridization for RANKL mRNA was performed and scored semiquantitatively based on the magnification at which the signal was first detected. There were 17 patients (M:F=8:9) with a median age of 15 years. Nine patients were children under 18 years of age. In 10 patients, tumors were characterized as GCT-like and in 7, non-GCT-like; 6 occurred in the setting of a known associated syndrome. Of the sporadic tumors, 9/11 (82%) were classified as aggressive. Fifteen of 17 (88%) tumors strongly expressed RANKL (8/9 aggressive, 2/2 nonaggressive; 10/10 GCT-like and 5/7 non-GCT-like). Two patients with clinically aggressive CGCL, GCT-like histology and high tumor RANKL expression were identified as candidates for a trial of denosumab with notable clinical response. CGCLs demonstrate strong and diffuse RANKL mRNA expression in mononuclear stromal cells, regardless of histology or presence of an associated syndrome. Denosumab may be clinically beneficial in aggressive CGCLs.

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.

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., (© 2018 American Cancer Society.)

Chordoma is a rare malignant tumor of bone with high morbidity and mortality. Recently, aggressive pediatric poorly differentiated chordoma with SMARCB1 loss has been described. This study summarizes the clinicopathologic features of poorly differentiated chordoma with SMARCB1 loss in the largest series to date. A search of records between 1990-2017 at MGH identified 19 patients with poorly differentiated chordoma. Immunohistochemical stains were evaluated. Kaplan-Meier survival statistics and log-rank (Mantel Cox) tests compared survival with other subtypes. The patients (n = 19) were diagnosed at a median age of 11 years (range: 1-29). Tumors arose in the skull base and clivus (n = 10/19; 53%); cervical spine (n = 6/19; 32%); and sacrum or coccyx (n = 3/19; 16%). The clinical stage of these patients (AJCC 7e) was stage 2A (n = 7/16; 44%); stage 2B (n = 6/16; 38%); stage 4A (n = 1/16; 6%); and stage 4B (n = 2/16; 13%). The tumors were composed of sheets of epithelioid cells with nuclear pleomorphism, abundant eosinophilic cytoplasm, and increased mitoses. Tumors were positive for cytokeratin (n = 18/18; 100%) and brachyury (n = 18/18; 100%). Patients were treated with a combination of excision, radiation therapy, and chemotherapy. No difference in overall survival, progression free survival, local control time, and metastasis free survival was identified between poorly differentiated chordoma of the skull base and of the spine. Compared to other chordoma subtypes, poorly differentiated chordoma has a significantly decreased mean overall survival after stratification by site (p = 0.037). Pediatric poorly differentiated chordoma has a distinct clinical and immunohistochemical profile, with characteristic SMARCB1 loss and decreased survival compared to conventional/chondroid chordoma. Recognition of this subtype is important because these malignancies should be treated aggressively with multimodality therapy.

Phosphaturic mesenchymal tumors typically cause paraneoplastic osteomalacia, chiefly as a result of FGF23 secretion. In a prior study, we identified FN1-FGFR1 fusion in 9 of 15 phosphaturic mesenchymal tumors. In this study, a total of 66 phosphaturic mesenchymal tumors and 7 tumors resembling phosphaturic mesenchymal tumor but without known phosphaturia were studied. A novel FN1-FGF1 fusion gene was identified in two cases without FN1-FGFR1 fusion by RNA sequencing and cross-validated with direct sequencing and western blot. Fluorescence in situ hybridization analyses revealed FN1-FGFR1 fusion in 16 of 39 (41%) phosphaturic mesenchymal tumors and identified an additional case with FN1-FGF1 fusion. The two fusion genes were mutually exclusive. Combined with previous data, the overall prevalence of FN1-FGFR1 and FN1-FGF1 fusions was 42% (21/50) and 6% (3/50), respectively. FGFR1 immunohistochemistry was positive in 82% (45/55) of phosphaturic mesenchymal tumors regardless of fusion status. By contrast, 121 cases of potential morphologic mimics (belonging to 13 tumor types) rarely expressed FGFR1, the main exceptions being solitary fibrous tumors (positive in 40%), chondroblastomas (40%), and giant cell tumors of bone (38%), suggesting a possible role for FGFR1 immunohistochemistry in the diagnosis of phosphaturic mesenchymal tumor. With the exception of one case reported in our prior study, none of the remaining tumors resembling phosphaturic mesenchymal tumor had either fusion type or expressed significant FGFR1. Our findings provide insight into possible mechanisms underlying the pathogenesis of phosphaturic mesenchymal tumor and imply a central role of the FGF1-FGFR1 signaling pathway. The novel FN1-FGF1 protein is expected to be secreted and serves as a ligand that binds and activates FGFR1 to achieve an autocrine loop. Further study is required to determine the functions of these fusion proteins.

Giant cell tumor (GCT) of bone is a locally aggressive benign neoplasm characterized by an abundance of osteoclastic giant cells that are induced by the neoplastic mononuclear cells; the latter express high levels of receptor activator of nuclear factor κ-B ligand (RANKL). Denosumab, a RANKL inhibitor, which is clinically used to treat GCT, leads to a marked alteration in the histologic appearance of the tumor with giant cell depletion and new bone deposition, leading to substantial histologic overlap with other primary tumors of bone. Most significantly, denosumab-treated GCT (tGCT) with abundant bone deposition may mimic de novo osteosarcoma, or GCT that has undergone malignant transformation. To histologically characterize tGCT, we identified 9 cases of GCT biopsied or resected after denosumab treatment. tGCT cases included 16 specimens from 9 patients including 6 female and 3 male individuals aged 16 to 47 (median 32) years. Duration of treatment varied from 2 to 55 months. We compared these tumors with malignant neoplasms arising in GCTs (n=9). The histology of tGCT was variable but appeared to relate to the length of therapy. All tGCTs showed marked giant cell depletion. Early lesions were highly cellular, and the combination of cellularity, atypia, and haphazard bone deposition caused the lesion to resemble high-grade osteosarcoma. Unlike de novo high-grade osteosarcoma or malignancies arising in GCT, however, tGCT showed less severe atypia, reduced mitotic activity, and lack of infiltrative growth pattern. Tumor in patients on prolonged therapy showed decreased cellularity and abundant new bone, deposited as broad, rounded cords or long, curvilinear arrays. The latter morphology was reminiscent of low-grade central osteosarcoma, but, unlike low-grade central osteosarcoma, tGCT was negative for MDM2 and again lacked an infiltrative growth pattern. Overall, tGCT may have a wide range of morphologic appearances. Because the treated tumors bear little resemblance to their pretreatment counterparts, careful attention to the history of denosumab administration is crucial to avoid a misdiagnosis with an important impact on therapy. Unlike malignant GCTs, tGCTs lack significant nuclear atypia, mitotic activity, and infiltration of preexisting bone, but instead show a unique pattern of intralesional bone deposition.

The genetics of myoepithelial tumors (ME) of soft tissue and bone have recently been investigated, with EWSR1-related gene fusions being seen in approximately half of the tumors. The fusion partners of EWSR1 so far described include POU5F1, PBX1, ZNF444 and, in a rare case, ATF1. We investigated by RNA sequencing an index case of EWSR1-rearranged ME of the tibia, lacking a known fusion partner, and identified a novel EWSR1-PBX3 fusion. The fusion was further validated by reverse transcriptase polymerase chain reaction and fluorescence in situ hybridization (FISH). To evaluate if this is a recurrent event, an additional cohort of 22 EWSR1-rearranged ME cases lacking a fusion partner were screened by FISH for abnormalities in PBX3 gene. Thus, two additional cases were identified showing an EWSR1-PBX3 gene fusion. One of them was also intraosseous involving the ankle, while the other occurred in the soft tissue of the index finger. The morphology of the EWSR1-PBX3 fusion positive cases showed similar findings, with nests or sheets of epithelioid to spindle cells in a partially myxoid to collagenous matrix. All three cases showed expression of S100 and EMA by immunohistochemistry. In summary, we report a novel EWSR1-PBX3 gene fusion in a small subset of ME, thereby expanding the spectrum of EWSR1-related gene fusions seen in these tumors. This gene fusion seems to occur preferentially in skeletal ME, with two of the three study cases occurring in intraosseous locations., (© 2014 Wiley Periodicals, Inc.)

The aberrant transcription factor EWS-FLI1 drives Ewing sarcoma, but its molecular function is not completely understood. We find that EWS-FLI1 reprograms gene regulatory circuits in Ewing sarcoma by directly inducing or repressing enhancers. At GGAA repeat elements, which lack evolutionary conservation and regulatory potential in other cell types, EWS-FLI1 multimers induce chromatin opening and create de novo enhancers that physically interact with target promoters. Conversely, EWS-FLI1 inactivates conserved enhancers containing canonical ETS motifs by displacing wild-type ETS transcription factors. These divergent chromatin-remodeling patterns repress tumor suppressors and mesenchymal lineage regulators while activating oncogenes and potential therapeutic targets, such as the kinase VRK1. Our findings demonstrate how EWS-FLI1 establishes an oncogenic regulatory program governing both tumor survival and differentiation., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Sclerosing epithelioid fibrosarcoma (SEF) is a rare, aggressive malignant neoplasm characterized by small nests and linear arrays of epithelioid cells embedded in a dense collagenous matrix. Very few primary SEFs of bone have been reported. Recognition is critical, as the dense extracellular collagenous matrix can be interpreted as osteoid, leading to misdiagnosis as-osteosarcoma. MUC4 and SATB2 are 2 recently characterized immunohistochemical markers for SEF and osteosarcoma, respectively. In reports to date, osteosarcomas are positive for SATB2 and negative for MUC4, whereas soft tissue SEFs have shown the opposite immunohistochemical profile (SATB2-/MUC4+). The purpose of this study was to characterize the clinicopathologic and immunohistochemical features of 8 primary SEFs of bone. The patients presented at a wide range of ages (25 to 73 y; median 52 y). Tumors mostly involved long bones of the extremities, with 3 cases involving the femur, 2 involving the ulna, and 1 involving the humerus. Other sites of involvement included the second rib (1) and the C6 vertebra (1). Follow-up information was available for 7 patients, 3 of whom developed metastases within 2 years of diagnosis. The other 4 patients were free of local recurrence or metastases at 1, 5, 12, and >84 months of follow-up, respectively. Radiographically, the tumors were predominantly lytic and poorly marginated. Histologically, 6 tumors showed pure SEF morphology, and 2 showed hybrid SEF/low-grade fibromyxoid sarcoma morphology. Focal dystrophic mineralization was seen in 1 case but was limited to areas of necrosis. None of the tumors showed the lace-like pattern of mineralization typical of osteosarcoma. The majority (6/8) of the tumors strongly expressed MUC4. SATB2 was negative in all but 1 case, which showed variable weak to moderate staining in ∼50% of nuclei. In general, the combination of morphology, MUC4 expression, and the absence of SATB2 expression was highly useful in arriving at the correct diagnosis.

Programmed cell death ligand 1 (PDL1, also known as B7H1) is a cell-surface protein that suppresses the cytotoxic CD8(+) T-cell-mediated immune response. PDL1 expression and its clinical relevance in sarcomas are not well understood. Therefore, we sought to measure RNA expression levels for PDL1 in 38 clinically annotated osteosarcoma tumor samples and aimed to determine if PDL1 expression correlates with clinical features and tumor-infiltrating lymphocytes (TIL). Quantitative real-time RT-PCR for PDL1 was optimized in 18 cell lines, of which 5 were osteosarcoma derived. qRT-PCR results were validated via flow cytometry and immunohistochemistry (IHC) in select cell lines. Total RNA was isolated from 38 human osteosarcoma samples for qRT-PCR analysis. Clinical data were sorted, and significance was determined by the Student t test. TILs were examined in patient samples by tissue microarray hematoxylin-eosin staining. We confirmed the constitutive PDL1 mRNA expression in cell lines by qRT-PCR, flow cytometry, and IHC. Across human osteosarcoma samples, PDL1 mRNA gene expression ranged over 4 log (>5,000-fold difference). Relative expression levels were evaluated against clinical factors such as age/gender, metastasis, recurrence, chemotherapy, percentage of necrosis, and survival; no significant associations were identified. The presence of TILs was associated with high PDL1 expression (R(2) = 0.37; P = 0.01). In summary, we developed an RNA-based assay to determine PDL1 expression levels, and we show, for the first time, that high levels of PDL1 are expressed in a subset of osteosarcoma, and PDL1 expression is positively correlated with TILs. Multiple agents targeting PD1/PDL1 are in clinical development, and this may be a novel immunotherapeutic strategy for osteosarcoma clinical trials., (©2014 American Association for Cancer Research.)

Background Context: Epithelioid hemangioma (EH) of bone is a benign vascular tumor that can be locally aggressive. It rarely arises in the spine, and the optimum management of EH of the vertebrae is not well delineated., Purpose: The report describes our experience treating six patients with EH of the spine in an effort to document the treatment of the rare spinal presentation., Study Design: This study is designed as a retrospective cohort study., Patient Sample: A continuous series of patients with the diagnosis of EH of the spine who presented at our institution., Outcome Measures: The clinical and radiographic follow-up of the patient population is documented., Methods: The Bone Sarcoma Registry at our institution was used to obtain a list of all patients diagnosed with EH of the spine. Medical records, radiographs, and pathology reports were retrospectively reviewed in all cases. Only biopsy-proven cases were included., Results: The six patients included five men and one woman who ranged in age from 20 to 58 years (with an average age of 40 years). The follow-up available for all six patients ranged from 6 to 115 (average 46.8) months. All patients presented with lytic vertebral body lesions. Five patients presented with pain secondary to their tumor, and the tumor in the sixth patient was found incidentally during the workup for a herniated disc. Three patients required surgical management for instability secondary to the destructive nature of their tumors, and two other patients required emergent decompression secondary to spinal cord compression by the tumor. The sixth patient was treated expectantly after biopsy confirmation. Three patients received postoperative radiation therapy as gross tumor remained after surgery. Three patients had gross total resections and did not receive postoperative radiation. Preoperative embolization was used in four patients. One patient continued to have back pain after surgery and radiation and another continued to have ataxia after surgery and radiation. No tumor locally recurred or progressed., Conclusions: Our data suggest that EH of the spine can be locally aggressive and lead to instability and cord compression. Surgery is required in such instances; however, observation should be considered in patients without instability or cord compression., (Copyright © 2013 Elsevier Inc. All rights reserved.)

The clinical and pathologic features of 8 primary myoepitheliomas of bone were analyzed. There were 5 female and 3 male patients who ranged in age from 16 to 49 (mean, 33.5) years. Three tumors arose in the ilium, 2 in the tibia, and 1 each in the maxilla, sacrum, and L1 vertebral body. Microscopically, the tumors had a solid, lobulated, reticular, or storiform growth pattern and were predominantly composed of spindle-shaped cells arranged in intersecting fascicles with eosinophilic cytoplasm. The round to polygonal epithelioid cells were arranged randomly or formed small clusters and contained variable amounts of eosinophilic or clear cytoplasm. Immunohistochemically, all the tumors were positive for vimentin and S100 protein, and 7 were positive for epithelial membrane antigen. No tumors were positive for keratin (AE1.3/CAM5.2). Smooth muscle actin was positive in 3 tumors and negative in 4, whereas desmin was negative in all 7 tumors tested. Nuclear staining for p63 was negative in 3 tested tumors. Staining for GFAP and CD34 was performed on 4 and 5 tumors, respectively, and all showed no expression. Fluorescence in situ hybridization for EWSR1 rearrangement was performed in 7 tumors. Five tumors (71%) showed the presence of EWSR1 gene rearrangement, and 2 were negative. Cytogenetic studies conducted on 1 tumor showed 46,XY,t(1;22)(q21;q12) associated with EWSR1-PBX1 fusion. Surgical procedures included curettage in 3 patients, resection in 3 patients, and 2 patients only had an open biopsy. Follow-up information was available for 4 patients; all remain free of disease with no recurrence. Although experience with primary myoepithelioma of bone is limited, histologically, banal tumors appear to behave in a benign manner, and conservative surgery appears to be sufficient treatment. Immunohistochemical and molecular analyses are helpful in their accurate identification.

Distinguishing chondrosarcoma from chondroblastic osteosarcoma can be difficult and highly subjective, especially on a small biopsy specimen. This distinction is critical in determining the most accurate prognosis and appropriate treatment modality, as adjuvant chemotherapy with surgery is standard treatment for osteosarcoma, whereas chondrosarcoma is generally treated by surgical excision alone. Cartilaginous neoplasms have recently been shown to frequently (56%) harbor gene mutations in the metabolic enzymes isocitrate dehydrogenase 1 (IDH1) and IDH2 (IDH1>IDH2), whereas other mesenchymal tumors lack these genetic aberrations. We investigated whether the presence of IDH1/2 mutations can be used to distinguish chondrosarcoma from chondroblastic osteosarcoma. Tumors including 25 predominantly high-grade chondrosarcomas and 65 osteosarcomas (44 chondroblastic osteosarcomas and 21 mixed osteosarcomas with a chondroblastic component) were evaluated, and a total of 59 cases (66%) were suitable for genotyping. Mutational analysis was performed using a multiplexed polymerase chain reaction genotyping platform to query for hotspot mutations in the genes IDH1 at codon R132. IDH1-negative cases underwent Sanger sequencing of IDH2 exon 4. No osteosarcomas (0/36) and 61% of chondrosarcomas (14/23) harbored a somatic mutation in IDH1/2, with the majority (86%) of mutations found in the IDH1 gene. IDH1/2 mutation analysis appears to be a promising biomarker for the distinction of chondrosarcoma from chondroblastic osteosarcoma. A positive result strongly favors the diagnosis of chondrosarcoma over chondroblastic osteosarcoma. The presence of IDH1/2 mutations can also help confirm the diagnosis of dedifferentiated chondrosarcoma when the tumor displays osteosarcomatous differentiation.

Objective: Enchondromas are benign lesions that may present with nonspecific features on imaging in children. Correlation of histology with imaging findings is often required to make the final diagnosis of a benign lesion. The aim of this study was to review imaging and pathological findings of enchondromas in children., Materials and Methods: Imaging examinations of 12 enchondromas in 11 patients (median age 14 years) were retrospectively reviewed. Imaging evaluation included an assessment of lesion size, relationship to the growth plate, mineralization, matrix and periosteal reaction, intrinsic MR signal characteristics, and intraosseous and soft-tissue edema. Pathological findings were reviewed., Results: Lesions were located in the phalanx in 33% (4 out of 12), metacarpal in 25% (3 out of 12), femur in 33% (4 out of 12) and tibia in 8% cases (1 out of 12). The mean size was 28 mm (range, 11-70 mm). Matrix mineralization in a typical "rings-and-arcs" pattern was observed in 20% of the lesions with available radiographs/CT (2 out of 10). Lesions were expansive with endosteal scalloping in 75% of cases (9 out 12) and contacted the growth plate in 50% of cases (6 out of 12). All enchondromas in which MR imaging was available (5 out of 5) demonstrated typical cartilaginous matrix of lobules of high T2 signal, low T1 signal, and peripheral enhancement., Conclusion: Enchondromas in children are relatively large lesions, with frequent endosteal scalloping and rare matrix mineralization.

The clinical and pathologic features of 50 epithelioid hemangiomas of bone are analyzed. There were 29 males and 21 females who ranged in age from 10 to 75 (mean 35) years. The tumors arose in long tubular bones (40%), short tubular bones of the distal lower extremity (18%), flat bones (18%), vertebrae (16%), and small bones of the hands (8%). Nine patients (18%) had involvement of more than 1 bone. Radiographically, the lesions were lucent and well marginated. Microscopically, the neoplasms had a lobular architecture and were composed of epithelioid endothelial cells that formed obvious vascular lumina or grew in solid sheets. No hyalinized or solid appearing extracellular myxoid matrix was present. Thirty-five patients were treated with curettage, 13 patients had a local resection and 2 patients only had a biopsy. One patient had local lymph node involvement. Three patients were treated with surgery and radiation therapy. Follow-up information revealed that 4 patients experienced a local recurrence; and 1 patient developed limited involvement of a regional lymph node. Epithelioid hemangioma of bone is a benign lesion that may be multifocal and affect separate tissue and is successfully treated with curettage or marginal en bloc excision.

Objective: The objective was to describe the imaging and histopathologic characteristics of metastatic myxoid liposarcomas., Materials and Methods: This retrospective study was approved by the institutional review board and complied with HIPAA guidelines. The study group comprised 12 patients with metastatic myxoid liposarcoma who underwent MRI, CT, or FDG-PET. The location and imaging characteristics of the metastatic lesions were recorded, and the histopathology of all metastatic lesions was reviewed., Results: There were 23 histologically proven metastases in 12 patients. Based on imaging criteria, there were 41 metastases. The mean time from the diagnosis of primary tumor to the first metastasis was 4.4 years. Sixty-seven percent of patients had bone and soft tissue metastases, 33% had pulmonary metastases, 33% had liver metastases, 25% had intra-abdominal, and 16% retroperitoneal metastases. CT demonstrated well-defined lobulated masses with soft tissue attenuation in all cases, without macroscopic fat component. In cases of osseous metastases, CT showed mixed lytic and sclerotic foci, with bone destruction in advanced cases. MRI demonstrated fluid-like signal intensity with mild heterogeneous enhancement in cases of soft tissue metastases. In osseous metastases, MRI showed avid heterogeneous enhancement. FDG-PET showed no significant FDG uptake for all metastases. MRI was the most useful imaging modality for osseous and soft tissue metastases., Conclusion: Myxoid liposarcomas are soft tissue sarcomas, with a high prevalence of extrapulmonary metastases. The bones and soft tissues were the most common site of involvement, followed by the lungs and liver. MRI was the most sensitive modality in the detection of osseous and soft tissue metastases, and is the recommended modality for the diagnosis and follow-up of bone and soft tissue involvement.

Ewing's sarcoma/primitive neuroectodermal tumor (EWS/PNET) is an aggressive neoplasm of bone and soft tissue. Histologically, it is characterized by the presence of small round blue cells, which usually express MIC-2 and FLI-1 immunohistochemically. The most specific feature for diagnosis, however, is cytogenetic or molecular evidence of a consistent abnormality, the t(11;22)(q24;q12), or variants thereof. The immunohistochemical expression of keratins in a significant proportion of these cases has been highlighted in several recent studies. The ultrastructural features of these keratin-positive tumors have not, however, been characterized in detail. In this study we analyzed the ultrastructural features of 12 well-documented EWS/PNETs that stained strongly for pankeratin by immunohistochemistry. Ultrastructurally, the tumor cells contained a few organelles, which included a small number of mitochondria, poorly developed Golgi complexes, free ribosomes, and inconspicuous rough-endoplasmic reticulum. Rudimentary cell junctions were seen in 2 tumors while prominent junctions were observed in the remaining 10. Five tumors contained intracytoplasmic filaments, and definite tonofibrils were identified in 2. Well-developed basal lamina around tumor cells were also demonstrated in 2 tumors. Follow-up information was available for all cases. Seven patients died of disease, 2 are alive with disease, and 3 have no current evidence of disease. The cohort includes 5 patients with a type-1 translocation, which has been associated with a better prognosis in some studies; 4 of these patients have died of their disease, and 1 is alive with recurrent disease. This study shows that keratin-positive EWS/PNETs have evidence of epithelial differentiation ultrastructurally, and may possibly represent a more aggressive subset of the EWS/PNET group of tumors.

The clinical and pathologic features of 10 epithelioid angiosarcomas of bone were analyzed. There were eight males and two females who ranged in age from 26 to 83 years (mean 62 years). Four tumors were solitary and six were multifocal. In two consultation cases, the submitted diagnosis was metastatic carcinoma. Microscopically, the tumor cells were arranged in solid and infiltrative sheets, and in most cases vascular channels or cystically dilated spaces were present. The neoplastic cells had abundant eosinophilic cytoplasm and large nuclei with open chromatin and prominent eosinophilic nucleoli. Intratumoral hemorrhage, neutrophilic infiltrates, and intracytoplasmic lumina were frequently present. All 10 tumors stained positive for one or more endothelial markers, with CD31 being the most sensitive marker. Seven cases stained positive for cytokeratin. Ultrastructural examination in three tumors confirmed their endothelial differentiation. In the absence of obvious vascular differentiation, abundant intratumoral hemorrhage and intratumoral neutrophils are useful ancillary morphologic features that may suggest a vascular origin. Six patients are dead of disease, one is alive with metastasis, and two patients are currently disease free. Epithelioid angiosarcoma of bone should be included in the differential diagnosis of epithelioid neoplasms of bone, and endothelial markers should be a part of their immunohistochemical analysis to avoid the misdiagnosis of a metastatic carcinoma because of the significant differences in the treatment and clinical outcomes of these entities.