Poorly differentiated chordoma: review of 53 cases

Chordoma: Genetics and Contemporary Management

Chordomas, arising from notochord remnants, are rare neoplasms with aggressive growth patterns despite their histologically low-grade nature. This review explores their embryological origins, molecular markers like brachyury, and genetic alterations driving pathogenesis. Diagnosis relies on advanced imaging and biopsy confirmation due to overlapping features with chondrosarcoma. The WHO classification distinguishes conventional, dedifferentiated, and poorly differentiated chordomas, each with distinct prognostic implications. Recent genomic analyses uncovered recurrent mutations in PI3K signaling pathways and chromatin remodeling genes, informing prognostic models. Surgery remains the cornerstone of treatment, though adjuvant radiation complements surgical resection. Although chordomas are generally considered refractory to medical therapy, emerging targeted molecular strategies show potential promise in ongoing trials. This review aims to provide a concise yet comprehensive overview of chordomas, guiding clinicians in diagnosis, treatment, and prognostication for improved patient outcomes.

A Rare Case of Adult Poorly Differentiated Chordoma of the Skull Base With Rapid Progression and Systemic Metastasis: A Review of the Literature

Chordoma is a rare tumor that arises from chordal tissue during fetal life. Recently, the concept of poorly differentiated chordoma, a subtype of chordoma characterized by loss of SMARCB1/INI1 with a poorer prognosis than conventional chordomas, was established. It predominantly occurs in children and is rare in adults. Here, we report a rare adult case of poorly differentiated chordoma of the skull base with a unique course that rapidly systemically metastasized and had the shortest survival time of any adult chordoma reported to date. The patient was a 32-year-old male with a chief complaint of diplopia. MRI showed a widespread neoplastic lesion with the clivus as the main locus. Endoscopic extended transsphenoidal tumor resection was performed. Pathological findings showed that the tumor was malignant, and immunohistochemistry revealed a Ki-67 labeling index of 80%, diffusely positive brachyury, and loss of INI1 expression. The final diagnosis was poorly differentiated chordoma. Postoperatively, the residual tumor in the right cavernous sinus showed rapid growth. The patient was promptly treated with gamma knife three fractions. The residual tumor regressed, but the tumor developed systemic metastasis in a short period, and the patient died seven months after diagnosis. This report of a rapidly progressing and fatal adult poorly differentiated chordoma shows the highest Ki-67 labeling index reported to date. Prompt multidisciplinary treatment should be considered when the Ki-67 labeling index is high.

SMARCB1/INI1 loss in skull base conventional chordomas: a clinicopathological and molecular analysis

Introduction

The loss of SMARCB1/INI1 protein has been recently described in poorly differentiated chordoma, an aggressive and rare disease variant typically arising from the skull base.

Methods

Retrospective study aimed at 1) examining the differential immunohistochemical expression of SMARCB1/INI1 in conventional skull base chordomas, including the chondroid subtype; 2) evaluating SMARCB1 gene deletions/copy number gain; and 3) analyzing the association of SMARCB1/INI1 expression with clinicopathological parameters and patient survival.

Results

65 patients (35 men and 30 women) affected by conventional skull base chordoma, 15 with chondroid subtype, followed for >48 months after surgery were collected. Median age at surgery was 50 years old (range 9-79). Mean tumor size was 3.6 cm (range 2-9.5). At immunohistochemical evaluation, a partial loss of SMARCB1/INI1 (>10% of neoplastic examined cells) was observed in 21 (32.3%) cases; the remaining 43 showed a strong nuclear expression. Fluorescence in situ hybridization (FISH) analysis was performed in 15/21 (71.4%) cases of the chordomas with partial SMARCB1/INI1 loss of expression. Heterozygous deletion of SMARCB1 was identified in 9/15 (60%) cases and was associated to copy number gain in one case; no deletion was found in the other 6 (40%) cases, 3 of which presenting with a copy number gain. No correlations were found between partial loss of SMARCB1/INI1 and the clinicopathological parameters evaluated (i.e., age, tumor size, gender, tumor size and histotype). Overall 5-year survival and 5-year disease-free rates were 82% and 59%, respectively. According to log-rank test analysis the various clinico-pathological parameters and SMARCB1/INI1 expression did not impact on overall and disease free-survival.

Discussion

Partial loss of SMARCB1/INI1, secondary to heterozygous deletion and/or copy number gain of SMARCB1, is not peculiar of aggressive forms, but can be identified by immunohistochemistry in a significant portion of conventional skull base chordomas, including the chondroid subtype. The variable protein expression does not appear to correlate with clinicopathological parameters, nor survival outcomes, but still, it could have therapeutic implications.

The NIH pediatric/young adult chordoma clinic and natural history study: Making advances in a very rare tumor

BACKGROUND

Chordomas are rare tumors arising from the skull base and spine, with approximately 20 pediatric chordoma cases in the Unitedn States per year. The natural history and optimal treatment of pediatric chordomas, especially poorly differentiated and dedifferentiated subtypes, is incompletely understood. Herein, we present findings from our first National Cancer Institute (NCI) chordoma clinic and a retrospective analysis of published cases of pediatric poorly differentiated chordomas (PDC) and dedifferentiated chordomas (DC).

METHODS

Patients less than 40 years old with chordoma were enrolled on the NCI Natural History and Biospecimens Acquisitions Study for Children and Adults with Rare Solid Tumors protocol (NCT03739827). Chordoma experts reviewed patient records, evaluated patients, and provided treatment recommendations. Patient-reported outcomes, biospecimens, and volumetric tumor analyses were collected. A literature review for pediatric PDC and DC was conducted.

RESULTS

Twelve patients (median age: 14 years) attended the clinic, including four patients with active disease and three patients with PDC responsive to systemic therapy. Consensus treatment, management, and recommendations were provided to patients. Literature review returned 45 pediatric cases of PDC or DC with variable treatments and outcomes.

CONCLUSIONS

A multidisciplinary expert clinic was feasible and successful in improving understanding of pediatric chordoma. While multimodal approaches have all been employed, treatment for PDC has been inconsistent and a recommended standardized treatment approach has not been defined. Centralized efforts, inclusive of specialized chordoma-focused clinics, natural history studies, and prospective analyses will help in the standardization of care for this challenging disease.

Lynch syndrome-associated chordoma with high tumor mutational burden and significant response to immune checkpoint inhibitors

Chordoma is a rare malignant bone tumor arising from notochordal tissue. Conventional treatments, such as radical resection and high-dose irradiation, frequently fail to control the tumor, resulting in recurrence and re-growth. In this study, genetic analysis of the tumor in a 72-year-old male patient with refractory conventional chordoma of the skull base revealed a high tumor mutational burden (TMB) and mutations in the MSH6 and MLH1 genes, which are found in Lynch syndrome. The patient and his family had a dense cancer history, and subsequent germline genetic testing revealed Lynch syndrome. This is the first report of a chordoma that has been genetically proven to be Lynch syndrome. Chordomas usually have low TMB; however, this is an unusual case, because the TMB was high, and immune checkpoint inhibitors effectively controlled the tumor. This case provides a basis for determining the indications for immunotherapy of chordoma based on the genetic analysis. Therefore, further extensive genetic analysis in the future will help to stratify the treatment of chordoma.

Imaging of spinal chordoma and benign notochordal cell tumor (BNCT) with radiologic pathologic correlation

Benign notochordal cell tumor (BNCT) and chordoma are neoplasms of notochordal differentiation. BNCT represents notochordal rests, commonly an incidental lesion present in the spine in 19% of cadaveric specimens. BNCTs are often radiographically occult. CT of BNCT frequently reveals patchy sclerosis between areas of maintained underlying trabeculae. BNCT demonstrates marrow replacement on T1-weighted MR images with high signal intensity on T2-weighting. BNCTs are frequently smaller than 35 mm and lack significant enhancement, bone destruction, cortical permeation, or soft tissue components. Biopsy or surgical resection of BNCT is usually not warranted, although imaging surveillance may be indicated. Chordoma is a rare low-grade locally aggressive malignancy representing 1-4% of primary malignant bone tumors. Chordoma is most frequent between the ages of 50-60 years with a male predilection. Clinical symptoms, while nonspecific and location dependent, include back pain, numbness, myelopathy, and bowel/bladder incontinence. Unfortunately, lesions are often large at presentation owing to diagnosis delay. Imaging of chordoma shows variable mixtures of bone destruction and sclerosis, calcification (50-70% at CT) and large soft tissue components. MR imaging of chordoma reveals multilobulated areas of marrow replacement on T1-weighting and high signal intensity on T2-weighting reflecting the myxoid component within the lesion and areas of hemorrhage seen histologically. Treatment of chordoma is primarily surgical with prognosis related to resection extent. Unfortunately, complete resection is often not possible (21-75%) resulting in high local recurrence incidence (19-75%) and a 5-year survival rate of 45-86%. This article reviews and illustrates the clinical characteristics, pathologic features, imaging appearance spectrum, treatment, and prognosis of BNCT and spinal chordoma.

A chronicle review of new techniques that facilitate the understanding and development of optimal individualized therapeutic strategies for chordoma

Chordoma is a rare malignant bone tumor that mainly occurs in the sacrum and the clivus/skull base. Surgical resection is the treatment of choice for chordoma, but the local recurrence rate is high with unsatisfactory prognosis. Compared with other common tumors, there is not much research and individualized treatment for chordoma, partly due to the rarity of the disease and the lack of appropriate disease models, which delay the discovery of therapeutic strategies. Recent advances in modern techniques have enabled gaining a better understanding of a number of rare diseases, including chordoma. Since the beginning of the 21st century, various chordoma cell lines and animal models have been reported, which have partially revealed the intrinsic mechanisms of tumor initiation and progression with the use of next-generation sequencing (NGS) techniques. In this study, we performed a systematic overview of the chordoma models and related sequencing studies in a chronological manner, from the first patient-derived chordoma cell line (U-CH1) to diverse preclinical models such as the patient-derived organoid-based xenograft (PDX) and patient-derived organoid (PDO) models. The use of modern sequencing techniques has discovered mutations and expression signatures that are considered potential treatment targets, such as the expression of Brachyury and overactivated receptor tyrosine kinases (RTKs). Moreover, computational and bioinformatics techniques have made drug repositioning/repurposing and individualized high-throughput drug screening available. These advantages facilitate the research and development of comprehensive and personalized treatment strategies for indicated patients and will dramatically improve their prognoses in the near feature.

Poorly Differentiated Chordoma of the Clivus With Loss of SMARCB1 Expression in a Pediatric Patient: A Case Report

Poorly differentiated chordoma (PDC) is a rare, aggressive subtype of chordoma. A two-year-old girl presented with cervical pain, limb paralysis and respiratory failure. Magnetic resonance imaging and positron emission tomography-computed tomography revealed a tumor compressing the pons at the clivus and osteoblastic metastatic lesions of the left upper arm and right iliac bone. Her tumors shrank substantially after treatment with chemotherapy and proton beam therapy. Our initial diagnosis was an atypical teratoma/rhabdoid tumor, but final diagnosis of PDC was made on the basis of the immunohistochemical expression of brachyury. In addition, the detection of SMARCB1/INI1 mutation confirmed the diagnosis of PDC.

Research hotspots and trends of chordoma: A bibliometric analysis

Background

Chordoma is a type of mesenchymal malignancy with a high recurrence rate and poor prognosis. Due to its rarity, the tumorigenic mechanism and optimal therapeutic strategy are not well known.

Methods

All relevant articles of chordoma research from 1 January 2000 to 26 April 2022 were obtained from Web of Science Core Collection database. Blibliometrix was used to acquire basic publication data. Visualization and data table of collaboration network, dynamic analysis, trend topics, thematic map, and factorial analysis were acquired using Blibliometrix package. VOSviewer was used to generate a visualization map of co-citation analysis and co-occurrence.

Results

A total of 2,285 articles related to chordoma were identified. The most influential and productive country/region was the United States, and Capital Medical University has published the most articles. Among all high-impact authors, Adrienne M. Flanagan had the highest average citation rate. Neurosurgery was the important periodical for chordoma research with the highest total/average citation rate. We focused on four hotspots in recent chordoma research. The research on surgical treatment and radiotherapy was relatively mature. The molecular signaling pathway, targeted therapy and immunotherapy for chordoma are not yet mature, which will be the future trends of chordoma research.

Conclusion

This study indicates that chordoma studies are increasing. Surgery and radiotherapy are well reported and always play fundamental roles in chordoma treatment. The molecular signaling pathway, targeted therapy, and immunotherapy of chordoma are the latest research hotspots.

Chordoma: To know means to recognize

Chordoma is a rare type of bone cancer characterized by its locally aggressive and destructive behavior. Chordoma is located in one of the three primary regions: skull base/clivus, sacrum or mobile spine. Chordoma grows slowly, therefore its insidious onset leads to delayed diagnosis, accounting for the low survival rates. Treatment centers around successful en bloc resection with negative margins, though, considering the anatomically constrained site of growth, it frequently requires adjuvant radiotherapy. This article analyzes the existing literature with the aim to provide a better insight in the current state of research in chordoma classification, characteristics, and management.

Prometastatic CXCR4 and Histone Methyltransferase EZH2 Are Upregulated in SMARCB1/INI1-Deficient and TP53-Mutated Poorly Differentiated Chordoma

Background: Chordoma is a rare tumor most commonly arising in the sacrococcygeal region from notochord remnants. Usually, these tumors are locally invasive and recurrent, and they have a 5–43% ability to metastasize. A newly-described aggressive variant called poorly differentiated chordoma is different from conventional chordoma in that it does not have the well-differentiated histologic appearance of conventional chordoma and also exhibits the loss of SMARCB1/INI1. Herein, we describe a case of poorly differentiated chordoma with SMARCB1/INI1 loss, a concurrent TP53 mutation, and Rb1 loss. Methods: The patient is a middle-aged man with a history of previously resected sacrococcygeal chordoma, who was found to have new hepatic, lung, and adrenal lesions. Results: Biopsy of the liver lesion showed sheets of malignant epithelioid cells with vacuolated cytoplasm, areas of necrosis, and up to five mitoses in one high-power field. No physaliferous cytologic features or matrix material was seen. After reviewing an extensive panel of immunohistochemical markers, the origin of the metastatic tumor could not be determined; the tumor was only positive for Cam5.2, EMA, and CD56. Brachyury was performed due to the patient’s previous history and was positive. Genomic testing showed a SMARCB1 mutation, TP53 mutation, and RB1 loss. Additional markers were performed, and the tumor showed a Ki-67 proliferation index of approximately 80%, mutant p53 protein, loss of INI1, and strong expression of both the histone methyl transferase EZH2 and the chemokine receptor CXCR4. Conclusions: Poorly differentiated chordoma is a highly aggressive variant of chordoma with few cases reported. This case of SMARCB1/INI-deficient, poorly differentiated chordoma also showed a concurrent TP53 mutation and loss of RB1, which resulted in malignant transformation with upregulation of both prometastatic CXCR4 and the histone methyltransferase EZH2, causing aggressive behavior and metastasis.

Dramatic In Vivo Efficacy of the EZH2-Inhibitor Tazemetostat in PBRM1-Mutated Human Chordoma Xenograft

Simple Summary

Chordomas are rare bone tumors characterized by a high recurrence rate. Presently, no medical treatment is available for advanced diseases due to the lack of molecular data and preclinical models. The current study showed the establishment and characterization of the largest panel chordoma xenografts, allowing pharmacological studies. In one PBRM1-mutated model, we demonstrated a strong therapeutic efficacy of the EZH2-inhibitor tazemetostat, encouraging further research on EZH2-inhibitors in chordomas.

Abstract

Chordomas are rare neoplasms characterized by a high recurrence rate and a poor long-term prognosis. Considering their chemo-/radio-resistance, alternative treatment strategies are strongly required, but their development is limited by the paucity of relevant preclinical models. Mutations affecting genes of the SWI/SNF complexes are frequently found in chordomas, suggesting a potential therapeutic effect of epigenetic regulators in this pathology. Twelve PDX models were established and characterized on histological and biomolecular features. Patients whose tumors were able to grow into mice had a statistically significant lower progression-free survival than those whose tumors did not grow after in vivo transplantation (p = 0.007). All PDXs maintained the same histopathological features as patients’ tumors. Homozygous deletions of CDKN2A/2B (58.3%) and PBRM1 (25%) variants were the most common genomic alterations found. In the tazemetostat treated PDX model harboring a PBRM1 variant, an overall survival of 100% was observed. Our panel of chordoma PDXs represents a useful preclinical tool for both pharmacologic and biological assessments. The first demonstration of a high antitumor activity of tazemetostat in a PDX model harboring a PBRM1 variant supports further evaluation for EZH2-inhibitors in this subgroup of chordomas.

Clinical response to nivolumab in an INI1-deficient pediatric chordoma correlates with immunogenic recognition of brachyury

Poorly differentiated chordoma (PDC) is a recently recognized subtype of chordoma characterized by expression of the embryonic transcription factor, brachyury, and loss of INI1. PDC primarily affects children and is associated with a poor prognosis and limited treatment options. Here we describe the molecular and immune tumour microenvironment profiles of two paediatric PDCs produced using whole-genome, transcriptome and whole-genome bisulfite sequencing (WGBS) and multiplex immunohistochemistry. Our analyses revealed the presence of tumour-associated immune cells, including CD8+ T cells, and expression of the immune checkpoint protein, PD-L1, in both patient samples. Molecular profiling provided the rationale for immune checkpoint inhibitor (ICI) therapy, which resulted in a clinical and radiographic response. A dominant T cell receptor (TCR) clone specific for a brachyury peptide-MHC complex was identified from bulk RNA sequencing, suggesting that targeting of the brachyury tumour antigen by tumour-associated T cells may underlie this clinical response to ICI. Correlative analysis with rhabdoid tumours, another INI1-deficient paediatric malignancy, suggests that a subset of tumours may share common immune phenotypes, indicating the potential for a therapeutically targetable subgroup of challenging paediatric cancers.

Loss of SMARCB1 promotes autophagy and facilitates tumour progression in chordoma by transcriptionally activating ATG5

OBJECTIVES

SWI/SNF-related matrix-associated actin-dependent regulator of chromatin subfamily B member 1 (SMARCB1) loss is associated with a poor prognosis in chordoma, while the mechanism remains largely unclear. Here, we aim to explore the function and regulatory mechanisms of SMARCB1 in chordoma.

MATERIALS AND METHODS

The effect of SMARCB1 on chordoma cells was investigated in vitro and in vivo. Chromatin immunoprecipitation (ChIP) sequencing was used to investigate the mechanisms of SMARCB1 in chordoma. The association between SMARCB1 and autophagy was validated by Western blot, immunofluorescence and transmission electron microscopy. In addition, the ATG5 expression in chordoma tissue was assessed using immunohistochemistry and correlated with patient survival.

RESULTS

SMARCB1 inhibited the malignant phenotype of chordoma cells in vitro and in vivo, supporting a tumour suppressor role of SMARCB1 in chordoma. ATG5-mediated autophagy was identified as a potential downstream pathway of SMARCB1. Mechanistically, SMARCB1 bound directly to the ATG5 promoter and epigenetically inhibited its transcription, which decreased ATG5 expression and impaired autophagy. Additionally, autophagy inhibitor chloroquine had a potential anti-cancer effect on chordoma cells in vitro. Moreover, high ATG5 expression was observed in recurrent chordoma patients, which independently correlated with adverse outcomes.

CONCLUSIONS

Taken together, our results revealed that the SMARCB1/ATG5 axis is a promising therapeutic target for chordoma and autophagy inhibitors may be effective agents for chordoma treatment.

Clinicopathological and Prognostic Characteristics in Dedifferentiated/Poorly Differentiated Chordomas: A Pooled Analysis of Individual Patient Data From 58 Studies and Comparison With Conventional Chordomas

Background

Currently, the clinicopathological and prognostic characteristics of dedifferentiated chordoma (DC) and poorly differentiated chordoma (PDC) remain poorly understood. In this study, we sought to characterize clinicopathological parameters in a large PDC/DC cohort and determine their correlations with progression-free survival (PFS) and overall survival (OS) of patients. We also attempted to compare clinical features between PDC/DC and conventional chordoma (CC).

Methods

Literature searches (from inception to June 01, 2020) using Medline, Embase, Google Scholar and Wanfang databases were conducted to identify eligible studies according to predefined criteria. The local database at our center was also retrospectively reviewed to include CC patients for comparative analysis.

Results

Fifty-eight studies from the literature and 90 CC patients from our local institute were identified; in total, 54 PDC patients and 96 DC patients were analyzed. Overall, PDC or DC had distinct characteristics from CC, while PDC and DC shared similar clinical features. Adjuvant radiotherapy and chemotherapy were associated with both PFS and OS in PDC patients in the univariate and/or multivariate analyses. In the DC cohort, tumor resection type, adjuvant chemotherapy and tumor dedifferentiation components significantly affected PFS, whereas none of them were predictive of outcome in the multivariate analysis. By analyzing OS, we found that surgery, resection type and the time to dedifferentiation predicted the survival of DC patients; however, only surgery remained significant after adjusting for other covariables.

Conclusions

These data may offer useful information to better understand the clinical characteristics of PDC/DC and may be helpful in improving the outcome prediction of patients.

Poorly differentiated chordoma showing loss of SMARCB1/INI1: Clinicopathological and radiological spectrum of nine cases, including uncommon features of a relatively under-recognized entity

Poorly differentiated chordoma is a newly recognized entity in the recent World Health Organization (WHO) classification of tumors of soft tissue and bone. Slightly over 60 such cases have been documented. Herein, we present a clinicopathological profile, including radiological features, of nine cases, which occurred in five males and four females, with age varying from 1 to 29 years (median = 43), in the cervical spine (n = 2), skull base (n = 2), clivus (n = 2), thoracic spine (n = 1) lumbar spine (n = 1) and coccyx (n = 1) Average tumor size was 4.8 cm. None of the 6-referral cases was diagnosed as a poorly differentiated chordoma at the referring laboratory. Histopathologically, all cases displayed a cellular tumor comprising polygonal cells (n = 9) displaying moderate to marked nuclear pleomorphism with prominent nucleoli (n = 7), eosinophilic (n = 9) to vacuolated cytoplasm (n = 7), rhabdoid morphology (n = 4), interspersed mitotic figures (n = 5), focal necrosis (n = 6) and inflammatory cells (n = 9). A single tumor displayed areas resembling classic chordoma, transitioning into poorly differentiated areas. There were multinucleate giant cells and physaliphorous cells in two tumors, each, respectively. Immunohistochemically, tumor cells were positive for AE1/AE3 (7/7), EMA (7/7), cytokeratin (CK) MNF116 (1/1), OSCAR (1/1), brachyury (9/9, diffusely), S100P (4/7, mostly focally), and glypican 3(2/4). SMARCB1/INI1 was completely lost in all nine tumors. A single case tested by FISH showed homozygous deletion of the SMARCB1 gene. Therapeutically (n = 7), all patients were treated with surgical resection (invariably incomplete) (n = 5), followed by adjuvant radiation therapy (n = 4) and chemotherapy (n = 4). While a single patient partially responded to treatment and another patient is alive with no evidence of disease after 23 years, three patients died of disease, six, eight, and 11 months post-diagnosis, despite adjuvant treatments. A single patient presented with a metastatic lung nodule, while another developed widespread metastasis. Poorly differentiated chordomas display a spectrum of features, are associated with a lower index of suspicion for a diagnosis, and display aggressive outcomes. Critical analysis of radiological and histopathological features, including necessary immunostains (brachyury and SMARCB1/INI1), is necessary for their timely diagnosis. These tumors show loss of SMARCB1/INI1 immunostaining and homozygous deletion of INI1/SMARCB1 gene.

Chordoma: Current status, problems, and future directions

Chordoma is a rare tumor that occurs along the axial spine in pediatrics and adults, with an incidence of approximately 350 cases per year in the United States. While typically described as slow-growing, many patients will eventually develop loco-regional relapse or metastatic disease with few treatment options. Despite numerous efforts over the last 10+ years, effective treatments for patients are lacking. As subtypes of chordoma are identified and described in more detail, further knowledge regarding the natural history of each type, tumor location, age differences, genomic variability, and an overall better understanding of chordoma may be the key to developing meaningful clinical trials and effective therapies for patients with chordoma.

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

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

Local Control After Proton Therapy for Pediatric Chordoma

PURPOSE

Due to the location and high dose required for disease control, pediatric chordomas are theoretically well-suited for treatment with proton therapy, but their low incidence limits the clinical outcome data available in the literature. We sought to report the efficacy and toxicity of proton therapy among a single-institution cohort.

METHODS AND MATERIALS

Between 2008 and 2019, 29 patients with a median age of 14.8 years (range, 3.8-21.8) received passive-scattered proton therapy for nonmetastatic chordoma. No patient received prior irradiation. Twenty-four tumors arose in the clivus/cervical spine region and 5 in the lumbosacral spine. Twenty-six tumors demonstrated classic well-differentiated histology and 3 were dedifferentiated or not otherwise specified. Approximately half of the tumors underwent specialized testing: 14 were brachyury-positive and 10 retained INI-1. Three patients had locally recurrent tumors after surgery alone (n = 2) or surgery + chemotherapy (n = 1), and 17 patients had gross disease at the time of radiation. The median radiation dose was 73.8 Gy relative biological effectivness (range, 69-75.6).

RESULTS

With a median follow-up of 4.3 years (range, 1.0-10.7), the 5-year estimates of local control, progression-free survival, and overall survival rates were 85%, 82%, and 86%, respectively. No disease progression was observed beyond 3 years. Excluding 3 patients with dedifferentiated/not-otherwise-specified chordoma, the 5-year local control, progression-free survival, and overall survival rates were 92%, 92%, and 91%, respectively. Serious toxicities included 3 patients with hardware failure or related infection requiring revision surgery, 2 patients with hormone deficiency, and 2 patients with Eustachian tube dysfunction causing chronic otitis media. No patient experienced brain stem injury, myelopathy, vision loss, or hearing loss after radiation.

CONCLUSIONS

In pediatric patients with chordoma, proton therapy is associated with a low risk of serious toxicity and high efficacy, particularly in well-differentiated tumors. Complete resection may be unnecessary for local control, and destabilizing operations requiring instrumentation may result in additional complications after therapy.

Desmoplastic myxoid tumor, SMARCB1-mutant: a new variant of SMARCB1-deficient tumor of the central nervous system preferentially arising in the pineal region

Desmoplastic myxoid tumor (DMT), SMARCB1-mutant is a recently proposed brain tumor that occurs in the pineal region of adults. This tumor is characterized by desmoplastic stroma and various degrees of myxoid matrix. Tumor cells with low-grade morphology show polyphenotypic immunoreactivity, and rhabdoid cells are rare. We herein present a case with some uncommon features such as no myxoid stroma and slightly elevated proliferating activity. To date, knowledge on the variety of SMARCB1/INI1-deficient tumors of the central nervous system is gradually increasing, encompassing highly aggressive to slow-growing varieties. DMT, SMARCB1-mutant seems to be relatively benign, but careful attention is necessary because SMARCB1/INI1 deficiency is generally a genetic signature of concern.

Poorly differentiated chordoma with whole-genome doubling evolving from a SMARCB1-deficient conventional chordoma: A case report

Evolution of poorly differentiated chordoma from conventional chordoma has not been previously reported. We encountered a case of a poorly differentiated chordoma with evidence of whole-genome doubling arising from a SMARCB1-deficient conventional chordoma. The tumor presented as a destructive sacral mass in a 43-year-old man and was comprised of a highly cellular poorly differentiated chordoma with small, morphologically distinct nodules of conventional chordoma accounting for <5% of the total tumor volume. Immunohistochemistry (IHC) revealed both components were strongly reactive for brachyury and lacked normal staining for INI1. Single nucleotide polymorphism (SNP) array analysis identified multiple genomic imbalances in the conventional component, including deletions of 1p, 3p, and 22q (involving SMARCB1) and loss of chromosomes 5 and 15, while the poorly differentiated component exhibited the same aberrations at a more profound level with additional loss of chromosome 4, low level focal deletion of 17p (involving TP53), and tetraploidy. Homozygous deletion of SMARCB1 was present in both components. Fluorescence in situ hybridization (FISH) analysis confirmed the relevant deletions in both components as well as genome doubling in the poorly differentiated tumor. This case suggests that SMARCB1 loss is an early event in rare conventional chordomas that could potentially evolve into poorly differentiated chordoma through additional genomic aberrations such as genome doubling. Further studies with additional patients will be needed to determine if genome doubling is a consistent pathway for evolution of poorly differentiated chordoma.

A case of desmoplastic myxoid tumor, SMARCB1 mutant, in the pineal region

Desmoplastic myxoid tumor (DMT), SMARCB1 mutant is a recently proposed new entity that mainly occurs in the pineal region and has epigenetic features similar to those of atypical teratoid/rhabdoid tumors (AT/RT)-MYC and poorly differentiated chordomas. Herein, we present a new case of a 33-year-old man with headaches, dizziness, nausea, vomiting, and blurred vision, who was initially found to have a suspicious germinoma on imaging. After surgical removal of the lesion, the postoperative pathological diagnosis was DMT, SMARCB1 mutant. To the best of our knowledge, this is the first case reported in China. Our findings also extend the range of the immunohistochemical phenotype of this rare tumor.

Chordomas: A review with emphasis on their pathophysiology, pathology, molecular biology, and genetics

Chordomas are uncommon, bone, axial, or (rarely) extra-axial tumors that are malignant and frequently recur but less commonly metastasize. They usually affect adults, with a very small proportion being pediatric tumors. For children, such tumors present a different biology, since they are more common as scull rather than sacral tumors, with aggressive histological features, including a loss of SMARCB1/INI1 and a dismal prognosis. Histologically, chordomas, believed to derive from notochordal tissue, characteristically show physaliphorous cells in a myxoid or chondroid matrix. Dedifferentiated and poorly differentiated forms can be observed. Moreover, a grading scale for chordomas has been proposed. Cytokeratin, EMA, S100, and brachyury are expressed by most chordomas. These are chemo-resistant tumors, for which surgical resection and/or radiotherapy are the treatments of choice. In this review, the histological, immunohistochemical, molecular, and clinical data of chordomas are discussed.

A Nonchordomatous-looking Chordoma: When INI-1 and Radiology Came to the Rescue!!!

SMARCB1/integrase interactor (INI)-1 is one of the core subunit proteins of the ATP-dependent SWI/SNF chromatin remodeling complex and acts as a tumor suppressor. INI-1 loss can be easily assessed using immunohistochemistry and is an important diagnostic clue for a histopathologist. Chordoma is a malignant tumor commonly occurring in the sacrococcygeal spine of adults and is characterized by nuclear expression of brachyury. Poorly differentiated chordoma, a morphologically and molecularly distinct entity, also shows nuclear brachyury positivity along with INI-1 loss. It usually occurs in children and has a predilection to involve the base of the skull. We describe a case of a poorly differentiated chordoma in a 5-year-old girl and discuss its unusual histomorphologic and immunohistochemical features.