Synchronous Low-Grade Central Osteosarcoma and Ewing Sarcoma: A Rare Case Report

A 23-year-old female patient presented with radicular back pain, perineal numbness, and urinary retention. The patient was diagnosed with cauda equina syndrome and magnetic resonance imaging (MRI) of the spine revealed an enhancing osseous lumbar lesion causing severe central stenosis. A core needle biopsy of the lumbar spine showed microscopic features compatible with a small round blue cell tumor. CD99 and FLI1 were positive in the tumor cells. Next-generation sequencing demonstrated a EWSR1::FLI1 fusion. Given these findings, the spine lesion was diagnosed as Ewing sarcoma. The patient underwent surgical decompression of L2. On further workup, an MRI revealed an ill-defined enhancing mass of the right distal femur. This area was biopsied, demonstrating a fibro-osseous lesion with osteoblast proliferation containing nuclear atypia, low mitotic activity, and SATB2 positivity, diagnosed as low-grade central osteosarcoma (LGCOS). The patient underwent resection, which showed a classic LGCOS by histomorphology. Although fluorescence in-situ hybridization study for MDM2 gene amplification was negative, the overall findings are most consistent with LGCOS. These neoplasms are considered to be synchronous due to the presentation of each entity within 6 months. Considering the aggregate yearly incidence of Ewing sarcoma (approximately 1 case per 750 000 per year) and LGCOS (approximately 1 case per 10 million per year), the aggregate yearly probability of developing both of these genetically unrelated tumors in a single individual is 1 per 7.5 trillion per year, and it is likely such an event has never happened in the past.

Dedifferentiated Low-Grade Osteosarcoma, Outcome with or Without Chemotherapy: A Systematic Review

The treatment of low-grade osteosarcomas is surgical resection with wide margins. In instances of dedifferentiation, a therapeutic paradigm similar to that of conventional high-grade osteosarcoma has not been adequately evaluated in these neoplasms. The main objective of this review was to define whether the addition of chemotherapy to surgical treatment has an impact on the survival of patients with dedifferentiated low-grade osteosarcomas. Secondary objectives were to observe the degree of histological response to neoadjuvant chemotherapy and to describe the percentage of de novo dedifferentiation. A systematic search of articles including dedifferentiated low-grade osteosarcomas, published between 1980 and 2022 was carried out in the PubMed, Cochrane and Scielo databases. A qualitative synthesis of the results was performed. Twenty-three articles comprising 117 patients were included. The survival of patients treated with surgery alone and surgery with chemotherapy was not statistically significant between the two groups. A good histological response was seen in 20% of specimens treated with neoadjuvant chemotherapy. De novo dedifferentiation was seen in approximately a fifth of low-grade osteosarcomas. The evidence available suggests that the addition of chemotherapy does not have an impact on the survival of patients with low-grade dedifferentiated osteosarcomas.

A clinical comparison between dedifferentiated low-grade osteosarcoma and conventional osteosarcoma

AIMS

The purpose of this study was to clarify the clinical behaviour, prognosis, and optimum treatment of dedifferentiated low-grade osteosarcoma (DLOS) diagnosed based on molecular pathology.

PATIENTS AND METHODS

We retrospectively reviewed 13 DLOS patients (six men, seven women; median age 32 years (interquartile range (IQR) 27 to 38)) diagnosed using the following criteria: the histological coexistence of low-grade and high-grade osteosarcoma components in the lesion, and positive immunohistochemistry of mouse double minute 2 homolog (MDM2) and cyclin-dependent kinase 4 (CDK4) associated with MDM2 amplification. These patients were then compared with 51 age-matched consecutive conventional osteosarcoma (COS) patients (33 men, 18 women; median age 25 years (IQR 20 to 38)) regarding their clinicopathological features.

RESULTS

The five-year overall survival (OAS) rates in the DLOS and COS patients were 85.7% and 77.1% (p = 0.728), respectively, and the five-year progression-free survival (PFS) rates were 57.7% and 44.9% (p = 0.368), respectively. A total of 12 DLOS patients received chemotherapy largely according to regimens for COS. Among the nine cases with a histological evaluation after chemotherapy, eight showed a poor response, and seven of these had a necrosis rate of < 50%. One DLOS patient developed local recurrence and five developed distant metastases.

CONCLUSION

Based on our study of 13 DLOS cases that were strictly defined by histological and molecular means, DLOS showed a poorer response to a standard chemotherapy regimen than COS, while the clinical outcomes were not markedly different. Cite this article: Bone Joint J 2019;101-B:745-752.

Low-grade central osteosarcoma in proximal humerus: a rare entity

Low-grade central osteosarcoma is a rare subtype of tumor with low-grade malignancy. Currently, wide resection with negative resection margin is the standard treatment for this disease. The role of neoadjuvant chemotherapy in low-grade central osteosarcoma was controversial and was mostly considered for tumors containing high-grade focal areas. Local tumor recurrences often exhibited a tumor with higher histologic grade or differentiation with the potential for metastases. In low-grade central osteosarcoma, timely wide resection after definite diagnosis can result in 5-year survival for almost 90%. However, the relatively nonspecific radiological and pathological findings make diagnosis very difficult. MDM2 and CDK4 are specific and provide sensitive markers for the diagnosis of low-grade central osteosarcoma, helping to differentiate low-grade central osteosarcoma from some benign lesions, including fibrous dysplasia, bone giant cell tumor, and chondrosarcoma. Here, we report the case of a 19-year-old woman with low-grade central osteosarcoma located at the proximal humerus. The affected site was rare, but the sensitive biomarkers CDK4 and MDM2 were positive. The patient recovered well after wide tumor resection following a proximal humerus endoprosthesis replacement. Our case highlighted the management strategies in low-grade central osteosarcoma. Being familiar with radiographic features, understanding the biological characteristics, and mastering diagnostic biomarkers can help oncologists avoid embarrassing situations in treatment when this rare tumor is highly suspected, even when located at an uncommon site. The discussion in this report focuses on radiographic and pathological features, advances of biomarkers that help in differential diagnosis, and current treatment options in low-grade central osteosarcoma.