Chromosome 12 long arm rearrangement covering MDM2 and RASAL1 is associated with aggressive craniofacial juvenile ossifying fibroma and extracranial psammomatoid fibro-osseous lesions

Abstract

To evaluate the diagnostic value of MDM2 status in craniofacial fibro-osseous lesions, we investigated MDM2 expression by immunohistochemistry and analyzed MDM2 amplification by qPCR in 30 cases of ossifying fibroma (including 13 cases of the juvenile variant) and 17 cases of fibrous dysplasia. Two cases of uncommon extragnathic psammomatoid fibrous dysplasia and a mixed control group of 15 cases of low-grade osteosarcoma and 15 cases of well-differentiated/dedifferentiated liposarcoma were included. MDM2 amplification was found in 33% of ossifying fibromas (peak of 69% for the juvenile variant) and in 12% of fibrous dysplasia, in none of which was MDM2 overexpressed. All control cases exhibited MDM2 amplification and overexpression. To investigate possible polysomy of chromosome 12, we studied RASAL1 amplification, a gene telomeric to MDM2 on the long arm of chromosome 12. RASAL1 amplification was reported in all benign fibro-osseous lesions exhibiting MDM2 amplification but not in controls. Simultaneous amplification of these two genes was significantly higher in juvenile ossifying fibromas compared with fibrous dysplasia (P ¼ 0.004), non-juvenile ossifying fibromas (P ¼ 0.001), and all other benign craniofacial fibro-osseous lesions combined (P ¼ 0.0001). Of the nine cases of juvenile ossifying fibroma exhibiting amplification, three were locally invasive and four were recurrent, suggesting aggressive disease. The two cases of extragnathic psammomatoid fibrous dysplasia also showed MDM2 and RASAL1 amplification with no MDM2 overexpression. This large chromosome 12 rearrangement, spanning MDM2 and RASAL1, is the first recurrent molecular abnormality to be reported in juvenile ossifying fibroma. It may represent both a molecular diagnostic marker and a characteristic of more aggressive forms with a higher risk of recurrence. Finally, the presence of this rearrangement in extragnathic psammomatoid fibro-osseous lesions mimicking ossifying fibromas might reflect a common molecular pathway in their pathogenesis and calls into question the classification of such lesions within fibrous dysplasia.

Ossifying fibromas of the jaws and craniofacial bones

“…18 However, neither markers are expressed in all low grade osteosarcomas and a more recent study has shown that MDM2 mutations and overexpression may be found in juvenile pasmmomatoid ossifying fibroma. 19 Prognosis and treatment A recurrence rate of 30e50% is reported and therefore complete, but conservative excision is required. Cases with malignant transformation have not been reported.…”

Updated systematic review: ossifying fibromas of the nose and paranasal sinuses

“…But the small number of cases and the presence of great confounding factors and more importantly the complete excision with no residual makes it difficult to make a firm conclusion. 10 In another study Tabareau et al studied 91 cases with BFOL and confirmed the presence of GNAS mutation to be specific to fibrous dysplasia among all BFOLs. Despite the low sensitivity, the presence of this genetic mutation can be useful to rule out OFs.…”

Osteosarcoma of the Jaw: Classification, Diagnosis and Treatment

“…These investigators also showed ampliication of an MDM2 neighbor, RASAL1, in all the ibro-osseous lesions with MDM2 ampliication but in none of the low-grade osteosarcomas studied [47].…”