Multifocal synchronous low-grade intramedullary and juxtacortical osteogenic sarcoma

Multifocal low-grade central osteosarcoma: a rare case

Low-grade central osteosarcoma (LGCOS) is a rare variant of osteosarcoma. We present a rare case of multifocal LGCOS located in two distinct skeletal sites, initially noted as incidental findings on imaging for distant traumatic pathology. Both sites seemed small and innocuous on initial imaging, and were quiescent clinically, illustrating the value of close interval multimodal surveillance scanning.

Bilateral synchronous tibial periosteal osteosarcoma with familial incidence

Multifocal or multicentric osteosarcoma (OS) has been described as tumor occurrence at two or more sites in a patient without visceral metastasis. These may be synchronous (more than one lesion at presentation) or metachronous (new tumor developing after the initial treatment). The incidence of multifocal OS has ranged from 1.5 to 5.4% in large series, with the synchronous type being rarer. Similarly, periosteal OS is another rare subtype of surface OS and constitutes less than 2% of all OS. An 11-year-old female was diagnosed with bilateral synchronous tibial periosteal OS, which were confirmed by CT-guided biopsies. After neoadjuvant chemotherapy, the patient underwent a staged wide local resection of the tumors. The defect was reconstructed with a proximal tibial replacement on the left side and autologous bone grafting on the right side. The patient did well after surgery and is free of disease at 5.5 years of follow-up. However, her brother also developed a right tibial periosteal osteosarcoma 4 years after her index surgery. Genetic analysis of blood sample from both patients showed a similar missense mutation in at least one allele of TP53 gene (exon 8). To the best of our knowledge, a case of bilateral 'synchronous' periosteal OS with a familial incidence has not been reported before.

MDM2 and CDK4 immunohistochemistry is a valuable tool in the differential diagnosis of low-grade osteosarcomas and other primary fibro-osseous lesions of the bone

Low-grade osteosarcoma is a rare malignancy that may be subdivided into two main subgroups on the basis of location in relation to the bone cortex, that is, parosteal osteosarcoma and low-grade central osteosarcoma. Their histological appearance is quite similar and characterized by spindle cell stroma with low-to-moderate cellularity and well-differentiated anastomosing bone trabeculae. Low-grade osteosarcomas have a simple genetic profile with supernumerary ring chromosomes comprising amplification of chromosome 12q13-15, including the cyclin-dependent kinase 4 (CDK4) and murine double-minute type 2 (MDM2) gene region. Low-grade osteosarcoma can be confused with fibrous and fibro-osseous lesions such as fibromatosis and fibrous dysplasia on radiological and histological findings. We investigated MDM2-CDK4 immunohistochemical expression in a series of 72 low-grade osteosarcomas and 107 fibrous or fibro-osseous lesions of the bone or paraosseous soft tissue. The MDM2-CDK4 amplification status of low-grade osteosarcoma was also evaluated by comparative genomic hybridization array in 18 cases, and the MDM2 amplification status was evaluated by fluorescence in situ hybridization or quantitative real-time polymerase chain reaction in 31 cases of benign fibrous and fibro-osseous lesions. MDM2-CDK4 immunostaining and MDM2 amplification by fluorescence in situ hybridization or quantitative real-time polymerase chain reaction were investigated in a control group of 23 cases of primary high-grade bone sarcoma, including 20 conventional high-grade osteosarcomas, two pleomorphic spindle cell sarcomas/malignant fibrous histiocytomas and one leiomyosarcoma. The results showed that MDM2 and/or CDK4 immunoreactivity was present in 89% of low-grade osteosarcoma specimens. All benign fibrous and fibro-osseous lesions and the tumors of the control group were negative for MDM2 and CDK4. These results were consistent with the MDM2 and CDK4 amplification results. In conclusion, immunohistochemical expression of MDM2 and CDK4 is specific and provides sensitive markers for the diagnosis of low-grade osteosarcomas, helping to differentiate them from benign fibrous and fibro-osseous lesions, particularly in cases with atypical radio-clinical presentation and/or limited biopsy samples.