A 12-year-old female presented with jaw pain and a firm mass involving the mandible. Imaging revealed an expansile lesion centered around the mandibular ramus with uniform and sclerotic density, root resorption, and prominence of involved periodontal ligament spaces. The patient underwent a hemi-mandibulectomy, which revealed a poorly demarcated tan mass surrounding and causing root resorption of the molar teeth. Histologic examination was performed.
1. Which of the following is a common molecular finding associated with this neoplasm?
2. True or False: The mandible is the most common site for this neoplasm.
Low-grade central osteosarcoma (LGCOS)
This is a low-grade central osteosarcoma (LGCOS), a rare intramedullary osteosarcoma that typically affects the metaphysis of long bones, predominantly the femur. It is commonly seen in young adults, and typically presents as a sclerotic expansile lesion on imaging.
Histologically, this lesion is composed of thick woven and lamellar bony trabeculae rimmed by osteoblasts and exhibiting pagetoid change, growing within a mildly hypercellular fibrosclerotic stroma. There are no mitotic figures or tumor necrosis. The tumor appears to infiltrate into the roots of the molar tooth with expansile growth into soft tissue. Fluorescence in-situ hybridization was performed and confirmed the presence of MDM2 amplification (12q13-q15), which is associated with this tumor. Of note, MDM2 amplification is similarly seen in other soft tissue tumors, including well-differentiated liposarcoma, dedifferentiated liposarcoma, and intimal sarcoma.
The main histologic differential diagnosis for this lesion is a benign fibro-osseous lesion such as fibrous dysplasia (FD). The latter does not invade cortical bone, teeth, or soft tissue, and does not exhibit MDM2 amplification. FD, however, has an activating missense mutation in GNAS gene. Parosteal osteosarcoma may have an identical histologic appearance as well as MDM2 amplification but arises from the cortical surface of bone.
Reference
- Nielson GP, Yoshida A, Bredella MA. et al. Low-grade central osteosarcoma. In: WHO Classification of Tumours Editorial Board. Soft tissue and bone tumours [Internet]. Lyon (France): International Agency for Research on Cancer; 2020 [cited 2024 Feb 1]. (WHO classification of tumours series, 5th ed.; vol. 3). Available from: https://tumourclassification.iarc.who.int/chapters/33/152
Quiz Answers
Q1 = B. MDM2 amplification
Q2 = False
Melad N. Dababneh, MBBS
head and neck pathology fellow, Cleveland Clinic
Ivan J. Stojanov, DMD
staff pathologist, Cleveland Clinic
