A Systemic Review of Primary Malignant Long Bone Tumors in Children and Adolescents.

PURPOSE OF THE STUDY: Managing bone tumours is complex, relying on limited evidence, expert opinions, and retrospective reviews. Multidisciplinary approaches and early diagnosis are crucial for better outcomes, especially in young patients with growing skeletons. The aim of this systemic review and meta-analysis is to give a comprehensive review of common malignant tumors affecting long bones in children and adolescents. MATERIAL AND METHODS: A PubMed/Medline search for "primary malignant long bone tumours in children" initially retrieved 1120 papers, which were subsequently narrowed down to 110 articles based on inclusion and exclusion criteria. These articles were reviewed, focusing on clinical presentation, diagnostic workup, treatment options, surgical planning, and variations in presentation, including rare tumours. The two most commonly reported tumours were osteosarcoma and Ewing sarcoma, leading to the division of studies into five groups. The inclusion criteria encompassed malignancies in patients aged 2-25 years, work-up, imaging, surgical treatment, rare tumour case reports, and surgical management principles, resulting in a heterogeneous group of articles. To enhance categorisation, it was clarified that studies with 10 or more cases were considered retrospective reviews. RESULTS: Reviewing of results thus demonstrate that the two likely tumours in children under consideration were osteosarcoma and Ewing sarcoma. Their presentation findings and clinical features were discussed in detail in the review. It is worth noting here that in case of differential diagnosis this should be the first on the list. DISCUSSION AND CONCLUSIONS: Although focus of literature is more on the two most common tumours. However, rare tumours should be considered as they can mimic these common tumors. KEY WORDS: primary, malignant, bone tumors, children, adolescent.

Primary Ewing's sarcoma of the uterine cervix: a case report and review of the literature.

BACKGROUND: Ewing's sarcoma (ES) is an aggressive cancer of bone and soft tissue, most of which tend to occur in the bone. Extraosseous Ewing's sarcoma (EES) of the cervix is extremely rare. CASE PRESENTATION: In the present work, we reported a 39-year-old cervical EES patient with a 2.5*2.1*1.8 cm tumor mass. According to previous literatures, our case is the smallest tumor found in primary cervical ES ever. The patient initially came to our hospital due to vaginal bleeding, and then the gynecological examination found a neoplasm between the cervical canal and partially in the external cervical orifice. The diagnosis of EES was confirmed below: Hematoxylin & Eosin staining (H&E) revealed small round blue malignant cells in biopsy specimens. Immunohistochemistry (IHC) showed the positive staining for CD99, NKX2.2, and FLI1. Disruption of EWSR1 gene was found by fluorescence in situ hybridization (FISH), and the EWSR1-FLI1 gene fusion was determined by next-generation sequencing (NGS). The patient received laparoscopic wide hysterectomy, bilateral adnexectomy, pelvic lymphadenectomy, and postoperative adjuvant chemotherapy and remained disease free with regular follow-up for 1 year. CONCLUSIONS: Through a systematic review of previously reported cervical ES and this case, we highlighted the importance of FISH and NGS for the accuracy of ESS diagnosis, which could assist on the optimal treatment strategy. However, due to the rarity of the disease, there is no standard treatment schemes. Investigation on molecular pathological diagnosis and standardization of treatment regimens for cervical ES are critical to patients' prognosis.

[Detection of EWSR1 gene rearrangement by fluorescence in situ hybridization in bone and soft tissue tumors: clinical application evaluation and atypical signal analysis].

Objective: To investigate the clinical application of EWSR1 gene rearrangement by fluorescence in situ hybridization (FISH) in bone and soft tissue tumors and to analyze the cases with atypical signal pattern. Methods: The cases detected for EWSR1 gene rearrangement by FISH in Beijing Jishuitan Hospital, Capital Medical University from 2014 to 2021 were collected, and the value of detecting EWSR1 gene rearrangement for diagnosing bone and soft tissue tumors was analyzed. The cases with atypical positive signals were further analyzed by next generation sequencing (NGS). Results: FISH using EWSR1 break-apart probe kit was successfully performed in 97% (205/211) of cases, 6 cases failed. Four of the 6 failures were due to improper decalcification, 1 case due to signal overlap caused by thick slices, and 1 case due to signal amplification and disorder. EWSR1 gene rearrangements were positive in 122 cases (122/205, 59%), atypical positive signal in 8 cases (8/205, 4%), and negative in 75 cases (75/205, 37%). In cases testing positive, the percentage of positive cells ranged from 34% to 98%, with 120 cases (120/122, 98%) showing a positive cell percentage greater than 50%. Among the 205 successfully tested cases, 156 cases were histologically diagnosed as Ewing's sarcoma, of which 110 were positive (110/156, 71%), 7 were atypical positive (7/156, 4%), and 39 were negative (39/156, 25%). Nine cases were histologically diagnosed as clear cell sarcoma of soft tissue, of which 6 were positive (6/9), 1 was atypical positive (1/9), and 2 were negative (2/9). Five cases were histologically diagnosed as extraskeletal myxoid chondrosarcoma, of which 2 were positive (2/5) and 3 were negative (3/5). Three cases were histologically diagnosed as angiomatoid fibrous histiocytoma, of which 2 were positive (2/3) and 1 was negative (1/3). Two cases were histologically diagnosed as myoepithelioma of soft tissue, of which 1 was positive (1/2) and 1 was negative (1/2). One case was histologically diagnosed as olfactory neuroblastoma with a positive result. The 29 other tumor cases including osteosarcoma, synovial sarcoma, and malignant melanoma and others were all negative. Basing on histology as the standard for diagnosis and considering atypical positive cases as negative, comparing with the 29 cases of other tumors as control group, the sensitivity for diagnosing Ewing's sarcoma through the detection of EWSR1 gene rearrangement was 71%, and the specificity was 100%; the sensitivity for diagnosing clear cell sarcoma of soft tissue was 67%, and the specificity was 100%; the sensitivity for diagnosing extraskeletal myxoid chondrosarcoma was 40%, and the specificity was 100%; the sensitivity for diagnosing angiomatoid fibrous histiocytoma was 67%, and the specificity was 100%; the sensitivity for diagnosing myoepithelioma of soft tissue was 50%, and the specificity was 100%; the sensitivity for diagnosing olfactory neuroblastoma was 100%, and the specificity was 100%. Four of 8 cases with atypical positive signals analyzed by NGS showed EWSR1 rearrangement, including EWSR1::FLI1 in one case of Ewing sarcoma, EWSR1::NFATC2 in one case of EWSR1::NFATC2-rearranged sarcoma, EWSR1::ATF1 in one case of clear cell sarcoma of soft tissue and EWSR1::NR4A3 in one case of extraskeletal myxoid chondrosarcoma. Conclusions: Detection of EWSR1 rearrangement by FISH is of utmost significance in the diagnosis of bone and soft tissue tumors. Cases with atypical positive signals should be further scrutinized, correlating with their histomorphology and verifying by NGS if necessary.

Extraskeletal Ewing's sarcoma of supraglottis: A rare case report.

Ewing's Sarcoma family of tumors is a group of small round tumor cells. Ewing's sarcoma majority occurs in bone, accounts about 10 % of primary bone tumors. Extraskeletal Ewing's sarcoma (ESS) is unusual and commonly seen in trunk, paravertebral, and chest wall region. It is rarely seen in head and neck region, accounting to 2-3 %. In head and neck region, ESS is seen in nasal or oral cavities, sinuses. EES originating in the larynx is very rare. Here, we report a 22 years old female having the complaints of change in voice and noisy breathing who was diagnosed as a case of EES of supraglottis. As the disease progressed during the time of diagnosis, she had to undergo emergency tracheostomy. The disease was inoperable so she received neoadjuvant chemotherapy followed by radiation followed by adjuvant chemotherapy. At present she is symptomatically better. The aim of this report is to put forward the rare site of Ewing's Sarcoma and highlighting the early diagnosis in suspected case with IHC, providing effective multimodality treatment.

Malignant tumour in pregnancy: Ewing-like sarcoma of the gluteal region.

We report a case of an Ewing-like sarcoma of the gluteal region with ongoing growth during the second trimester of pregnancy and noted during the third trimester. This lesion was consequently studied to infer its malignant potential. Several examinations were conducted to characterise this lesion, such as ultrasound and MR, which showed signs of tumourous invasion of the deep tissues of the gluteal region.Given that the pregnancy was at the end of the third trimester, the decision was made to schedule the delivery at 37 weeks of gestation and treat the tumour afterwards to balance maternal and fetal health.This case illustrates the need for a detailed investigation and guidance by a multidisciplinary team to provide prenatal counselling regarding a malignant tumour during pregnancy.

Acontractile detrusor as an initial presentation of sacral spinal cord lesion: Case series.

OBJECTIVES: This study aims to investigate cases of acontractile bladder as the initial presentation of benign and malignant spinal conditions. The focus is on the challenges in making a diagnosis and the importance of a thorough neurological evaluation. METHODS: We conducted a retrospective case series involving three patients who exhibited symptoms of acontractile bladder. Detailed clinical histories, urodynamic studies, and imaging techniques such as lumbosacral magnetic resonance imaging (MRI) were analyzed. Histopathological findings from relevant biopsies were also taken into account. RESULTS: Case 1: A 14-year-old female presented with urinary retention, back pain, and an acontractile bladder on urodynamic study. Further examination, including lumbosacral MRI and histopathology, confirmed a diagnosis of metastatic Ewing's Sarcoma. Case 2: A 39-year-old female with urinary incontinence and elevated post-void residual exhibited delayed bladder sensation. Lumbar spine MRI revealed a grade I Schwannoma after surgical resection. Case 3: A 15-year-old male with lower urinary tract symptoms and an acontractile detrusor on urodynamic study was found to have a Tarlov cyst on lumbosacral MRI. CONCLUSION: Atonic or Underactive bladder syndrome may be the initial presentation of a serious spinal condition. Complete neurological evaluation is mandatory if no obvious clinical cause.

CIC-Rearranged Sarcoma.

CIC-rearranged sarcoma is a rare type of small round cell sarcoma. The tumors often affect the deep soft tissues of patients in a wide age range. They are highly aggressive, respond poorly to chemotherapy, and have a worse outcome than Ewing sarcoma. CIC-rearranged sarcoma has characteristic and recognizable histology, including lobulated growth, focal myxoid changes, round to epithelioid cells, and minimal variation of nuclear size and shape. Nuclear ETV4 and WT1 expression are useful immunohistochemical findings. CIC fusion can be demonstrated using various methods; however, even next-generation sequencing suffers from imperfect sensitivity, especially for CIC::DUX4.

FLI-1 is expressed in a wide variety of hematolymphoid neoplasms: a special concern in the differential diagnosis.

Friend Leukemia Virus Integration 1 (FLI-1) is a member of E26 transformation-specific family of transcription factors that participates in hematopoietic and vascular endothelial cell development. Immunohistochemical detection of FLI-1 has been widely used to diagnose vascular tumors or, more evidently, Ewing's sarcoma. However, the expression pattern of FLI-1 in hematolymphoid neoplasms remains unclear. Therefore, in this study, we aimed to investigate the expression of FLI-1 in these tumors, focusing on high-grade lesions, which presents a diagnostic challenge by mimicking Ewing's sarcoma. We evaluated the expression FLI-1 in various types of lymphoid and plasmacytic tumors, including 27 plasmablastic lymphomas, 229 diffuse large B-cell lymphomas, 22 precursor T- or B-lymphoblastic lymphomas, 24 angioimmunoblastic-type nodal T-follicular helper cell lymphomas, 52 peripheral T-cell lymphomas, NOS, 18 Burkitt lymphomas, 18 non-gastric lymphomas of mucosa-associated lymphoid tissue, 38 chronic lymphocytic leukemia/small lymphocytic lymphomas, 15 mantle cell lymphomas, 23 gastric MALT lymphomas, 50 plasma cell myelomas, and 38 follicular lymphomas. We calculated the H-scores of FLI-1 immunostaining, ranging from 0 to 200, and used the scores to analyze the clinicopathological significance of FLI-1 statistically. FLI-1 was expressed to varying degrees in all types of hematological tumors. FLI-1 expression was detected in 84.1% of patients (466/554). FLI-1 was highly expressed in precursor T- or B-lymphoblastic lymphomas. Follicular lymphomas exhibited low FLI-1 expression. In plasmablastic lymphoma, 85.2% of the patients were focally positive for FLI-1. FLI-1 expression did not correlate with clinicopathological variables, such as demographic data or disease stage, in patients with plasmablastic lymphoma and diffuse large B-cell lymphoma. However, FLI-1 overexpression was associated with poorer overall survival in patients with plasmablastic lymphoma. This study demonstrates that FLI-1 is expressed in various hematolymphoid neoplasms. FLI-1 expression can lead to diagnostic confusion, especially in small blue round cell tumors, such as lymphoblastic lymphoma, plasmablastic lymphoma, and plasma cell myeloma, when distinguishing tumors positive for CD99 and CD56 without CD3, CD20, or CD45. Our findings also suggested the possibility of FLI-1 as a potential prognostic biomarker for plasmablastic lymphoma.

Adamantinoma-Like Ewing Sarcoma Mimicking Merkel Cell Carcinoma in the Parotid Gland: A Diagnostic Pitfall.

Adamantinoma-like Ewing sarcoma (ALES) is a newly described rare entity, which shows EWSR1::FLI1 rearrangement characteristic of Ewing sarcoma. This can be diagnostically challenging as it manifests histologically with epithelial differentiation and has diffuse keratin expression as well as p40 and p60 positivity. We hereby report a case of ALES in a 33-year-old woman with a past medical history of breast carcinoma who presented with a right-sided parotid mass. CT scan of the neck showed a heterogenous mass within the superficial lobe, measuring 17 mm in diameter for which the patient underwent superficial parotidectomy. Histopathology of the mass revealed a malignant neoplasm formed of solid nests, cords and sheets of cells with minimal cytoplasm and monomorphic nuclei with granular chromatin and indistinct nucleoli. Brisk mitotic activity and tumor necrosis were also present. The tumor showed strong and diffuse reactivity for pankeratin (clone AE1/AE3) and keratin 20, both in a dot-like pattern, raising the suspicion of metastatic Merkel cell carcinoma; however, molecular studies showed EWSR1::FLI1 rearrangement, supporting the diagnosis of ALES. In summary, it is prudent to have knowledge about this entity to avoid its misdiagnosis as other malignancies of the head and neck region which exhibit a different clinical course, prognosis and hence treatment modalities.

[Ewing's sarcoma of central nervous system: a clinicopathological analysis of six cases].

Objective: To investigate the clinicopathological characteristics, pathological diagnosis of Ewing's sarcoma of the central nervous system. Methods: Six cases of Ewing's sarcoma of the central nervous system diagnosed at the First Affiliated Hospital of Nanjing Medical University, Nanjing, China from 2015 to 2022 were collected. The clinical manifestations, histological morphology, immunophenotype and molecular genetics of these cases were analyzed. The related literature was reviewed. Results: There were four males and two females, with a male to female ratio of 2∶1. The onset age was 17-40 years, with a median age of 23 years. All 6 tumors were located in the spinal cord (2 cases of cervical vertebra, 1 case of thoracic vertebra, 2 cases of lumbar vertebra, and 1 case of sacral vertebra). The patients' clinical manifestations were mostly lumbago, weakness and numbness of lower limbs/limbs. In 1 case, the tumor recurred and metastasized to the suprasellar region and the third ventricle. Microscopically, the tumor showed diffuse infiltrative growth. In some cases, the tumor was closely related to the spinal meninges. The tumor cells were arranged in sheet, lobular, thin-rope, and nest-like patterns. Homer-Wright rosette was visible. The tumor cells were small to medium in size, and most of them had scant cytoplasm. A few cells had clear cytoplasm. Some areas were rhabdoid. The tumor cell nuclei showed focal mild pleomorphism. The chromatin was uniform and delicate while the nucleoli were not obvious. Mitosis was commonly seen. The tumor was separated by fibrous connective tissue and may be accompanied by mucinous degeneration. Immunohistochemistry showed that all tumors were positive for CD99, NKX2.2, Fli1, ERG. ATRX, H3K27me3, INI1 and BRG1 were all retained. Immunohistochemical stains for EMA, GFAP and Olig2 were negative. The Ki-67 proliferation index was 30%-70%. EWSR1 break-apart FISH test was positive. Conclusions: Ewing's sarcoma is rare in the central nervous system and needs to be distinguished from a variety of neoplasms with primitive undifferentiated small cell morphology. Immunohistochemistry and molecular genetics may be required for a proper diagnosis.

Detection of early prognostic biomarkers for metastasis of Ewing's sarcoma in pediatric patients.

AIMS: Ewing's Sarcoma is an extremely aggressive tumor in children. The disease is associated with highly metastatic rate, especially at the time of diagnosis, contributing to a lower survival rate and poor prognosis. The study aimed to identify predictive biomarkers for metastatic Ewing's sarcoma through in-depth analysis of the plasma proteome profile of pediatric Ewing's sarcoma patients. MAIN METHODS: Plasma samples from Ewing's sarcoma patients and control individuals were profiled using both shotgun and dimethyl-labeled proteomics analysis. Subsequently, Ewing's sarcoma patients were further stratified according to their metastatic state and chemotherapy response. Western blot was used for validation. Univariate and multivariate analyses were performed to determine proteome metastasis predictors. Receiver operating characteristic (ROC) analysis was done to assess the diagnostic significance of the potential plasma Ewing's sarcoma biomarkers. KEY FINDINGS: Our results revealed a set of proteins significantly associated with the metastatic Ewing's sarcoma disease profile. These proteins include ceruloplasmin and several immunoglobulins. Additionally, our study disclosed significant differentially expressed proteins in pediatric Ewing's sarcoma, including CD5 antigen-like, clusterin, and dermcidin. Stable isotope dimethyl labeling and western blot further confirmed our results, strengthening the impact of such proteins in disease development. Furthermore, an unbiased ROC curve evaluated and confirmed the predictive power of these biomarker candidates. SIGNIFICANCE: This study presented potential empirical predictive circulating biomarkers for determining the disease status of pediatric Ewing's sarcoma, which is vital for early prediction.

A Practical Approach to Small Round Cell Tumors Involving the Gastrointestinal Tract and Abdomen.

Small round cell neoplasms are diagnostically challenging owing to their clinical and pathologic overlap, necessitating use of large immunopanels and molecular analysis. Ewing sarcomas (ES) are the most common, but EWSR1 is translocated in several diverse neoplasms, some with round cell morphology. Molecular advances enable classification of many tumors previously termed 'atypical ES'. The current WHO Classification includes two new undifferentiated round cell sarcomas (with CIC or BCOR alterations), and a group of sarcomas in which EWSR1 partners with non-Ewing family transcription factor genes. This article reviews the spectrum of small round cell sarcomas within the gastrointestinal tract and abdomen.

[Clinical and morphological characteristics of Ewing's sarcoma and the algorithm for diagnosing undifferentiated round cell sarcomas]. / Kliniko-morfologicheskaya kharakteristika sarkomy Yuinga i algoritm diagnostiki nedifferentsirovannykh kruglokletochnykh sarkom.

BACKGROUND: The group of undifferentiated round cell sarcomas, according to the World Health Organization Classification, in addition to Ewing's sarcoma (ES), includes round cell sarcoma with rearrangement of the EWSR1 gene with partners not from the ETS gene family, sarcoma with BCOR gene alterations, CIC -rearranged sarcoma. Despite the fact that all tumors have clear histological and immunological criteria, their diagnosis can be difficult, given the fact that there are overlapping variants of the morphological picture and immunophenotype both within the group and with other round cell tumors. OBJECTIVE: Present a comparative analysis of genetically verified ES, sarcoma with BCOR gene alterations and CIC-rearranged sarcoma. MATERIAL AND METHODS: A comparative study of biopsy specimens of bones, soft tissues and internal organs was carried out in 118 patients with ES, 10 with BCOR gene alterations and 8 with CIC-rearranged sarcomas. All cases were genetically verified. The following research methods were used: histological, immunohistochemical, RT-PCR, RNA sequencing and FISH. RESULTS: Within our cohort, it was shown that ES predominantly affects bones, while soft tissue localization is more typical for the other two undifferentiated round cell sarcomas. Histologically, in the overwhelming majority of cases, ES is characterized by a monomorphic round-cell structure; on the contrary, heterogeneous structure is typical for sarcoma with alterations of the BCOR gene, CIC-rearranged sarcoma. High sensitivity and specificity of CD99/NKX2.2 co-expression for ES, BCOR/SATB2/TLE1 for sarcoma with BCOR gene alterations, high specificity and low sensitivity of WT1/ETV4 co-expression for CIC-rearranged sarcoma was shown. CONCLUSION: For the differential diagnosis of undifferentiated round-cell sarcomas, it is necessary to take into account the clinical, morphology when compared with the data of the IHC study, and verification by molecular genetic methods is necessary to improve the accuracy of diagnosis.

Simple and easily accessible prognostic markers in ewing sarcoma; neutrophil-lymphocyte ratio, neutrophil-platelet score and systemic-inflammation index.

Background: Inflammation markers are the new point of view in cancer due to increasing data on the interaction of immune system with tumor cells and their prognostic and predictive importance were found in many different types of solid tumors. Therefore, we aimed to evaluate the prognostic value of neutrophil-lymphocyte ratio (NLR), neutrophil-platelet score (NPS), and systemic inflammation index (SII) in Ewing sarcoma patients in which risk groups are still not clearly defined. Methods and Results: A total of 64 patients were evaluated retrospectively. Receiver operating characteristic analysis was performed to find cut-off values for NLR and SII. Survival analysis was calculated by using Kaplan-Meier method. Cox regression analysis was performed to determine prognostic factors such as age, stage, and neoadjuvant chemotherapy were statistically significant prognostic factors for OS in multivariate analysis. While patients with low NLR and SII had longer OS (P = 0.003 and P = 0.018), patients with high NPS score had shorter OS (67.7 vs 21.7 months, P = 0.001). Conclusion: Patients with lower NLR, NPS, and SII score have a better prognosis compared with those with higher NLR, NPS, and SII score and these simple parameters may be monitoring tools of the tumor microenvironment.

Clinical features and outcomes of infantile soft-tissue sarcoma: A multicenter retrospective study in Beijing.

Background: Soft-tissue sarcomas during infancy are rare and understudied. With no data on this specific condition, we performed a retrospective study of infant-onset sarcomas based on a multi-institutional cohort in Beijing, China, collected over the past decade. We reviewed infantile soft-tissue sarcomas' clinical characteristics, treatments, and outcomes. Materials and Methods: The patients with soft-tissue sarcoma diagnosed from 0 to 12 months in four primary children's hospitals in Beijing from January 2010 to December 2019 were evaluated. Results: Fifty-one patients were enrolled, including 31 males and 20 females. The median age at the diagnosis was five months (range, 0-12), and seven (13.7%) patients were diagnosed in the first month of their life. Histologically, twenty-five patients were diagnosed with rhabdomyosarcoma (RMS), six were diagnosed with extraosseous Ewing sarcoma (EES), and twenty were diagnosed with nonrhabdomyosarcoma soft-tissue sarcoma (NRSTS). The treatment principles and details of RMS focused on reference to the Intergroup Rhabdomyosarcoma Study Group (IRSG) protocols. For EES and NRSTS, chemotherapy was prescribed according to children's oncology group protocols. The five-year EFS/OS rates of RMS were 26.4% ± 19.5%/56.2 ± 17.8%, the five-year EFS/OS rate of EES was 50% ± 20.4%, and the five-year EFS/OS of NRSTS was 85.2% ± 9.8%/100%. Conclusions: Infant-onset soft-tissue sarcoma is heterogeneous. The primary location of the abdominal or pelvic cavity of RMS and EWS was at a later stage and had a poorer prognosis. Multimodal therapy resulted in successful disease control for the majority of patients. Standardization of treatment protocols will facilitate care for such challenging conditions.

Recognizing and treating patients with Ewing sarcoma.

ABSTRACT: This article reviews the cause, presentation, diagnosis, and management of Ewing sarcoma, the second most common primary bone malignancy in children and young adults. Recent research has provided advances in understanding the cause of Ewing sarcoma as well as improved treatment regimens. However, much is still unknown and additional research is needed to continue to improve the overall prognosis, which ranges from 70% to 80% 5-year survival for patients with localized disease. Improving clinician knowledge about Ewing sarcoma will help shorten time to diagnosis and improve survival rates.

Assessment of the Interval to Diagnosis in Pediatric Bone Sarcoma.

OBJECTIVES: The timely diagnosis of primary bone malignancies in pediatric patients is critical to clinical outcomes. The purpose of this study is to investigate the initial presentation of pediatric bone sarcoma patients to an academic health care system and assess the current interval to diagnosis. METHODS: We conducted a retrospective review of pediatric patients (aged 1-18) with biopsy-proven diagnosis of osteosarcoma or Ewing sarcoma presenting between 2004 and 2020. All living patients had 1 year or more of follow-up. Primary outcomes were interval to diagnosis, clinical features on initial presentation, percent of patients with negative radiographic workup at initial presentation, and number of health care encounters before diagnosis. RESULTS: Seventy-one patients (osteosarcoma, 51; Ewing sarcoma, 20) were included. Average age at presentation was 13.1 ± 3.3 years (range, 4.4-18.3). Average symptom duration was 5.4 ± 13.9 months (range, 0.1-84). Clinical features at initial presentation included limb/back pain (91.5% of patients), activity modification/pain medication use (78.9%), palpable mass (40.8%), night pain (35.2%), limp (25.4%), limb disuse (18.3%), and recent fever history (2.8%). Fourteen of 71 patients (19.7%) had negative radiographs at initial presentation. Average number of health care encounters before diagnosis was 1.9 ± 0.6 (range, 1.0-4.0), with most in the outpatient pediatrician clinics (81.2%) and emergency department (18.3%). Average time to diagnosis from initial presentation was 19.5 ± 65 days (range, 0-493); the 14 patients with initial negative radiographs had a statistically significant prolonged interval to diagnosis of 54 ± 134 days (range, 0-493; P = 0.018). CONCLUSIONS: We found pediatric patients with primary bone sarcoma present with an average interval to diagnosis of 20 days. Twenty percent of patients had a significantly prolonged interval to diagnosis of 54 days. Clinical features suggest night pain is not a sensitive indicator. In patients of appropriate age with persistent unilateral pain in suspicious locations, early advanced imaging with magnetic resonance imaging should be considered.