Nonrandom chromosome breakpoints at Xq26 and 2q33 characterize cemento-ossifying fibromas of the orbit

Assessment of MDM2 Gene Locus Amplification by Fluorescence In-Situ Hybridization in Juvenile Ossifying Fibroma

Juvenile ossifying fibroma (JOF) is an uncommon benign fibro-osseous lesion (BFOL) of the maxillofacial bones with a locally aggressive nature and a high recurrence rate. Murine Double Minute 2 (MDM2) is an oncogene located at chromosome 12 (12q13-15) that inhibits the tumor suppressor gene TP53. The presence of MDM2 gene locus amplification is a useful molecular adjunct in the evaluation of some sarcomas, including low-grade intramedullary osteosarcoma (LGIOS). JOF and LGIOS have some overlapping clinical and histopathological features. The aim of this study is to evaluate a series of JOF for the presence of MDM2 gene locus amplification using fluorescence in-situ hybridization (FISH).

MATERIALS AND METHODS

With IRB approval, a search of the institutional files of the archives of the Oral Pathology and Surgical Pathology biopsy services at the University of Florida Health was performed. The cases were re-evaluated by an oral pathology resident, an oral and maxillofacial pathologist, and a bone and soft tissue pathologist. Cases with consensus in diagnosis were selected (n = 9) for MDM2 testing. Testing by FISH for MDM2 gene locus amplification was applied to all retrieved cases.

RESULTS

The examined cases were all negative for MDM2 gene locus amplification via FISH testing.

CONCLUSION

In our small series, JOF did not demonstrate MDM2 gene locus abnormality, a characteristic of LGIOS. This finding suggests that JOF has a distinct underlying pathogenesis. If confirmed in a larger series, these findings may be useful in distinguishing these two entities in cases with overlapping features or when minimal biopsy material is available.

Pediatric Gnathic Bony and Mesenchymal Tumors

Evaluation of bone pathology within the head and neck region, particularly the gnathic bonesis is complex, demonstrating unique pathologic processes. In part, this variation is due to odontogenesis and the embryological cells that may be involved, which can contribute to disease development and histologic variability. As with any boney pathosis, the key is to have clinical correlation, particularly with radiographic imaging prior to establishing a definitive diagnosis. This review will cover those entities that have a predilection for the pediatric population, and while it is not all inclusive, it should serve as a foundation for the pathologist who is evaluating bony lesions involving the craniofacial skeleton.

Genomic Profiling of the Craniofacial Ossifying Fibroma by Next-Generation Sequencing

BACKGROUND

Ossifying fibroma (OF) of the craniofacial skeleton is a fibro-osseous lesion characterized by various patterns of bone formation in a cellular fibroblastic stroma. The molecular landscape of OF remains mostly unknown. There are a few known pathogenic abnormalities in OF, including HRPT2 mutations in conventional OF and SATB2 translocations in juvenile psammomatoid OF. On the other hand, conflicting reports exist regarding MDM2 gene amplification and chromosomal copy number alterations (CNA) in OF.

METHODS

Surgically removed biopsies and curettage specimens from OF patients were obtained. Clinical, radiographic, and pathologic features of tumors were reviewed. Genomic DNA was extracted from formalin-fixed, paraffin-embedded blocks of tumor tissue. Capture-based DNA next-generation sequencing targeting the coding regions 529 cancer genes and select introns was performed.

RESULTS

We identified 17 OF cases from 8 male and 8 female patients with mean age of 22 years (range 1-58 years). Nine case occurred in the gnathic bones and 8 in the extragnathic craniofacial bones. These cases included 3 juvenile psammomatoid OF, 6 conventional OF and 8 juvenile trabecular OF. Large-scale CNAs were present in 6 of 17 cases. Seven cases (41%) had focal amplifications including FOSB (n = 2, 11%), FOS (n = 4, 23%), COL1A1 (n = 4, 23%) and TBX3 (n = 5, 29%). Three cases (17%) had pathogenic CDC73 mutations. No cases showed focal MDM2 amplification.

CONCLUSIONS

Here, we provided a comprehensive molecular characterization of OF that reveals a heterogeneous genetic profile with occasional large-scale CNAs (n = 6, 35%). FOS, FOSB, and TBX3 genes that regulate AP-1 transcriptional complex are frequently altered in OF (n = 7, 41%), chiefly in juvenile trabecular OF. These genes encode transcription factors that act as downstream effectors of the MAP kinase signaling pathway. MDM2 amplification is an exceedingly rare event in OF, if present at all, so identification of this event should continue to raise concern for low-grade gnathic osteosarcoma. In summary, our findings suggest that OF represents a heterogeneous group of tumors at the genetic level but dysregulation of the AP-1 pathway may play a role in pathogenesis of juvenile trabecular OF.

Psammomatoid Ossifying Fibroma Is Defined by SATB2 Rearrangement

Psammomatoid ossifying fibroma (PsOF), also known as juvenile PsOF, is a benign fibro-osseous neoplasm predominantly affecting the extragnathic bones, particularly the frontal and ethmoid bones, with a preference for adolescents and young adults. The clinical and morphologic features of PsOF may overlap with those of other fibro-osseous lesions, and additional molecular markers would help increase diagnostic accuracy. Because identical chromosomal breakpoints at bands Xq26 and 2q33 have been described in 3 cases of PsOF located in the orbita, we aimed to identify the exact genes involved in these chromosomal breakpoints and determine their frequency in PsOF using transcriptome sequencing and fluorescence in situ hybridization (FISH). We performed whole RNA transcriptome sequencing on frozen tissue in 2 PsOF index cases and identified a fusion transcript involving SATB2, located on chromosome 2q33.1, and AL513487.1, located on chromosome Xq26, in one of the cases. The fusion was validated using reverse transcription (RT)-PCR and SATB2 FISH. The fusion lead to a truncated protein product losing most of the functional domains. Subsequently, we analyzed an additional 24 juvenile PsOFs, 8 juvenile trabecular ossifying fibromas (JTOFs), and 11 cemento-ossifying fibromas (COFs) for SATB2 using FISH and found evidence of SATB2 gene rearrangements in 58% (7 of 12) of the evaluable PsOF cases but not in any of the evaluable JTOF (n = 7) and COF (n = 7) cases. A combination of SATB2 immunofluorescence and a 2-color SATB2 FISH in our index case revealed that most tumor cells harboring the rearrangement lacked SATB2 expression. Using immunohistochemistry, 65% of PsOF, 100% of JTOF, and 100% of COF cases showed moderate or strong staining for SATB2. In these cases, we observed a mosaic pattern of expression with >25% of the spindle cells in between the bone matrix, with osteoblasts and osteocytes being positive for SATB2. Interestingly, 35% (8 of 23) of PsOFs, in contrast to JTOFs and COFs, showed SATB2 expression in <5% of cells. To our knowledge, this is the first report that shows the involvement of SATB2 in the development of a neoplastic lesion. In this study, we have showed that SATB2 rearrangement is a recurrent molecular alteration that appears to be highly specific for PsOF. Our findings support that PsOF is not only morphologically and clinically but also genetically distinct from JTOF and COF.

First presentation of a frameshift mutation in the SETD2 gene of a juvenile psammomatoid ossifying fibroma (JPOF) associated with an aneurysmal bone cyst

Background

The rarity of juvenile psammomatoid ossifying fibroma (JPOF) and lack of cytogenetic studies prompted us to report a novel SETD2 gene mutation in a benign odontogenic tumour.

Case presentation

A 21-year-old man presented with a hard, expanded mandibular cortex. Computed tomography revealed multilocular radiopacity in the mandible; this was reconstructed via segmental mandibulectomy using a vascularised iliac crest flap. Based on the clinical and histological findings, we diagnosed JPOF associated with an aneurysmal bone cyst. Microscopically, the solid area was characterised by many rounded or angular ossicles in a cellular fibrous stroma. The stromal cells were spindle-like or stellate. Next-generation sequencing detected a frame shift mutation of the SETD2 gene, while the copy number was normal.

Conclusions

Our findings suggest further genetic studies should be performed to assess whether this mutation is related to tumour genesis. 

Spheno-orbital juvenile psammomatoid ossifying fibroma: a case report and literature review

Ossifying fibroma (OF) is an uncommon benign fibro-osseous lesion. Based on its clinical, morphological, and radiological features, OF is further divided into cemento-ossifying fibroma (COF), juvenile psammomatoid ossifying fibroma (JPOF), and juvenile trabecular ossifying fibroma (JTOF). JPOF rarely involves the cranial base, with limited reports published on spheno-orbital JPOF. In this paper, we report a case of JPOF of the greater wing of the sphenoid bone and lateral orbital wall in an 11-year-old child and show a surgical video. Although rare, JPOF should be considered in the differential diagnosis of fibro-osseous lesions of the spheno-orbital region.

Juvenile psammomatoid ossifying fibroma of the parietal bone and review of calvarial presentations: illustrative case

BACKGROUND

Juvenile psammomatoid ossifying fibroma (JPOF) is an uncommon benign fibro-osseous lesion that only rarely presents in the calvaria.

OBSERVATIONS

The authors reported a case of JPOF in the left parietal bone of a 20-year-old patient and reviewed the 27 other cases of JPOF occurring in the calvaria as reported in the literature.

LESSONS

JPOF rarely presents in the calvaria, and because diagnosis is a histopathologic one, clinicians should consider this entity when presented with a lytic, expansile mass on imaging. Little is known about the molecular mechanisms driving development of JPOF. MDM2 amplification may play a role, although this was not seen in the case presented herein.

Parafibromin Abnormalities in Ossifying Fibroma

Ossifying fibromas are very rare tumors that are sometimes seen as part of the hyperparathyroidism-jaw tumor syndrome (HPT-JT), which is caused by inactivating mutations of the HRPT2/CDC73 tumor suppressor gene. CDC73 mutations have been identified in a subset of sporadic cases but aberrant expression of the encoded protein, parafibromin, has not been demonstrated in ossifying fibroma. We sought to determine if loss of parafibromin regularly contributes to the development of sporadic, nonsyndromic ossifying fibroma. We examined a series of 9 ossifying fibromas, including ossifying, cemento-ossifying, and juvenile active variants, for parafibromin protein expression by immunohistochemistry and for CDC73 sequence abnormalities by Sanger sequencing and/or targeted AmpliSeq panel sequencing. Four ossifying fibromas showed a complete absence of nuclear parafibromin expression; loss of parafibromin expression was coupled with aberrant cytoplasmic parafibromin expression in 1 case. CDC73 mutations were detected in 2 cases with aberrant parafibromin expression. These results provide novel evidence, at the level of protein expression, that loss of the parathyroid CDC73/parafibromin tumor suppressor may play a role in the pathogenesis of a subset of ossifying fibromas.

Copy number alteration profiling facilitates differential diagnosis between ossifying fibroma and fibrous dysplasia of the jaws

Ossifying fibroma (OF) and fibrous dysplasia (FD) are two fibro-osseous lesions with overlapping clinicopathological features, making diagnosis challenging. In this study, we applied a whole-genome shallow sequencing approach to facilitate differential diagnosis via precise profiling of copy number alterations (CNAs) using minute amounts of DNA extracted from morphologically correlated microdissected tissue samples. Freshly frozen tissue specimens from OF (n = 29) and FD (n = 28) patients were obtained for analysis. Lesion fibrous tissues and surrounding normal tissues were obtained by laser capture microdissection (LCM), with ~30–50 cells (5 000–10 000 µm²) per sample. We found that the rate of recurrent CNAs in OF cases was much higher (44.8%, 13 of 29) than that in FD cases (3.6%, 1 of 28). Sixty-nine percent (9 of 13) of the CNA-containing OF cases involved segmental amplifications and deletions on Chrs 7 and 12. We also identified eight CNA-associated genes (HILPDA, CALD1, C1GALT1, MICALL2, PHF14, AIMP2, MDM2, and CDK4) with amplified expression, which was consistent with the copy number changes. We further confirmed a jaw lesion with a previous uncertain diagnosis due to its ambiguous morphological features and the absence of GNAS mutation as OF based on the typical Chr 12 amplification pattern in its CNA profile. Moreover, analysis of a set of longitudinal samples collected from an individual with a cellular lesion in suspicion of OF at the first surgery, recurrence and the latest malignant transformation revealed identical CNA patterns at the three time points, suggesting that copy number profiling can be used as an important tool to identify borderline lesions or lesions with malignant potential. Overall, CNA profiling of fibro-osseous lesions can greatly improve differential diagnosis between OF and FD and help predict disease progression.

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

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=0.004), non-juvenile ossifying fibromas (P=0.001), and all other benign craniofacial fibro-osseous lesions combined (P=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.

Fibro-osseous lesions of the craniofacial skeleton: an update

Benign fibro-osseous lesions of the craniofacial skeleton (BFOL) are a variant group of intraosseous disease processes that share similar microscopic features characterized by hypercellular fibroblastic stroma containing various combinations of bone or cementum-like tissue and other calcified structures [1-6]. Whereas some are diagnosable histologically, most require a combined assessment of clinical, microscopic and radiologic features. Some BFOL of the craniofacial complex are unique to that location whereas others are encountered in bones from other regions. Reactive, neoplastic, developmental and dysplastic pathologic processes are included under the rubric of BFOL and treatment varies from disease to disease. This review will discuss the clinical, microscopic and radiologic aspects of the more important types of BFOL of the craniofacial complex with updated information on underlying genetic and molecular pathogenic mechanisms of disease. Four main groups of BFOLs will be addressed.

Juvenile ossifying fibroma: Psammamatoid variant

Juvenile ossifying fibroma is a rare fibro-osseous lesion containing variable amount of calcified masses, which resembles bone or cementum within a fibrocellular connective tissue stroma. It has variable clinical behavior, highly aggressive in nature including invasion and destruction of adjacent anatomic structures with a strong tendency to recur. We reported a 28-year-old female patient with a growth in the upper left vestibule region extending from canine to molar region with clinical, histopathological, and radiological features are presented. Surgical management was done, and regular follow-up was advised.

Juvenile psammomatoid ossifying fibroma: a review

In WHO classification of odontogenic tumors (2005), juvenile ossifying fibroma (JOF) is divided into juvenile psammomatoid ossifying fibroma (JPOF) and juvenile trabecular ossifying fibroma (JTOF). JPOF has been distinguished because of its location, clinical behavior, and age of occurrence. It is generally seen in younger age group and the most common site is paranasal sinuses, orbits, and fronto-ethmoidal complex. Radiologically, the internal structure can be radiolucent, mixed, or radiopaque, depending on the degree of calcification and extent of the cystic changes. Histologically, it is characterized by a densely cellular fibrous stroma interspersed with numerous psammoma bodies. The treatment is "en bloc" surgical excision while in case of intracranial extension, tumor removal may need a combination of neurosurgical and transfacial approach. Malignant transformation and metastasis has not been reported but recurrence is common. The purpose of this narrative review article is to discuss the various aspects of JPOF reported in the English medical literature.

Benign fibro-osseous lesions of the craniofacial complex. A review

Benign fibro-osseous lesions of the craniofacial complex are represented by a variety of disease processes that are characterized by pathologic ossifications and calcifications in association with a hypercellular fibroblastic marrow element. The current classification includes neoplasms, developmental dysplastic lesions and inflammatory/reactive processes. The definitive diagnosis can rarely be rendered on the basis of histopathologic features alone; rather, procurement of a final diagnosis is usually dependent upon assessment of microscopic, clinical and imaging features together. Fibrous dysplasia and osteitis deformans constitute two dysplastic lesions in which mutations have been uncovered. Other dysplastic bone diseases of the craniofacial complex include florid osseous dysplasia, focal cemento-osseous dysplasia and periapical cemental dysplasia, all showing a predilection for African descent individuals; although no specific genetic alterations in DNA coding have yet to be uncovered and most studies have been derived from predominant high African descent populations. Ossifying fibromas are neoplastic lesions with four subtypes varying with regard to behavior and propensity for recurrence after surgical excision. The clinicopathologic and molecular features of this unique yet heterogeneous group of diseases are reviewed.

Cytogenetic distinction among benign fibro-osseous lesions of bone in children and adolescents: value of karyotypic findings in differential diagnosis

Benign fibro-osseous lesions of bone (BFOL) comprise a group of clinically distinct entities with significant histologic overlap and often occur in children and adolescents. Because of prior studies indicating that these lesions possess distinct karyotypic abnormalities, we conducted a retrospective review of cytogenetic analyses performed in a series of 16 BFOL in children and adolescents diagnosed at two institutions. These comprised five cases with the diagnosis of ossifying fibroma, four with osteofibrous dysplasia, and seven with fibrous dysplasia arising in the skeleton of 16 children and adolescents. All cases were analyzed using standard G-banding techniques on fresh tumors explanted in tissue culture media. Spectral karyotyping (SKY) and fluorescence in situ hybridization (FISH) were used to analyze selected metaphases of a talar lesion with the histologic features of ossifying fibroma. All four confirmed ossifying fibromas, including the talar lesion, contained clonal aberrations fusing breakpoints on Xq26 and 2q33, and one case with dissimilar histology did not. Three of four osteofibrous dysplasias contained multiple copies of chromosomes 8, 12, and/or 21. All but two fibrous dysplasia cases exhibited either a completely normal karyotype or single cell aberrations. One fibrous dysplasia had subtle chromosomal abnormalities not seen in other cases in the series, and another had complex abnormalities involving multiple chromosomes. Our current and published results indicate that cytogenetics might be of ancillary use in the diagnosis of BFOL and that a characteristic chromosomal arrangement is associated with ossifying fibroma.

Psammomatoid and trabecular juvenile ossifying fibroma of the craniofacial skeleton: two distinct clinicopathologic entities

The term juvenile ossifying fibroma is used in the literature in naming 2 microscopically distinct fibro-osseous lesions of the craniofacial skeleton. One is characterized by small uniform spherical ossicles resembling psammoma bodies (psammomatoid juvenile ossifying fibroma). The other is distinguished by trabeculae of fibrillary osteoid and woven bone (trabecular juvenile ossifying fibroma). Three new cases of each type are reported, and the literature is extensively reviewed for published cases of these 2 entities.Psammomatoid juvenile ossifying fibroma is reported more commonly than trabecular juvenile ossifying fibroma. It affects patients from a wider age range (3 months to 72 years) and an older mean age range (16-33 years) as compared with 2 to 12 years and 8(1/2) to 12 years, respectively, for trabecular juvenile ossifying fibroma. In both types there is a slight male predominance and the lesions are unencapsulated and tend to infiltrate adjacent bone. A significant difference between the 2 tumors is their site of occurrence. Although psammomatoid juvenile ossifying fibroma occurs predominantly in the sinonasal and orbital bones, trabecular juvenile ossifying fibroma predominantly affects the jaws. Aggressive growth occurs in some-but not all-cases of both types. Such behavior may be related to younger patient age and the concurrent development of aneurysmal bone cysts, which is seen more frequently in psammomatoid juvenile ossifying fibroma. This study demonstrates that not only histologic but also demographic and clinical differences between psammomatoid juvenile ossifying fibroma and trabecular juvenile ossifying fibroma warrant their classification as 2 distinct clinicopathologic entities.