case_images: PMC11006978_01
case_images: Axial CT image showed a mandible mass (red arrow), destroying bone cortex and extending into surrounding soft tissue, without periosteal reaction (A). Gross specimen revealed a 5x4x3cm mass with a pale cut surface and focal hemorrhage (B).
case_images: fonc-14-1369046-g001.jpg
case_images: PMC11006978_01_fonc-14-1369046-g001.jpg
case_images: f1
case_images: Axial CT image demonstrated a 5x3 cm mass in right mandible, extending into surrounding soft tissue ( Figure 1A ). After partial mandibulectomy, gross specimen revealed a 5x4x3cm mass with a pale cut surface and focal hemorrhage ( Figure 1B ).
case_images: Representative morphological characteristics of the mandibular tumor. Under extra-low power field, H&E slides displayed a lobulated mandible mass destroying bone cortex (black arrows) (A) and intramedullary invasion (B). Heterogeneous tumor cells accompanied with a few multinucleated giant cells under low power view (green arrows) (C). Mononuclear tumor cells exhibited epithelioid feature with varying cell density (D-F). Focally, epithelioid cells and spindle cells were present in varying proportions, forming biphasic structure (G-I). Prominent pseudoglandular structure embedded in the spindle tumor cells (H, I). The tumor was mainly composed of a mixture of histiocyte-like cells, larger epithelioid cells and osteoclast-like giant cells (J-L). High power field exhibited two principal cell types: small histiocyte-like cells with pale cytoplasm and round or reniform nuclei, and larger epithelioid cells with amphophilic cytoplasm (J, K). Scattered lymphocytes infiltration (K). Numerous osteoclast-like multinucleated giant cells infiltrated focally (L).
case_images: fonc-14-1369046-g002.jpg
case_images: PMC11006978_01_fonc-14-1369046-g002.jpg
case_images: f2
case_images: H&E slides showed a lobulated tumor destroying bone cortex ( Figure 2A ) and intramedullary invasion ( Figure 2B ). Heterogeneous tumor cells accompanied with a few multinucleated giant cells ( Figure 2C ). Figures 2D-F ). Focally, the tumor was consisted of biphasic structure, with varying proportions of epithelioid and spindle cells ( Figures 2G-I ). Prominent pseudoglandular structure embedded in the spindle tumor cells, which was similar to biphasic synovial sarcoma to some extent ( Figures 2H, I ). Generally, the tumor was composed of a mixture of histiocyte-like cells, larger epithelioid cells, and osteoclast-like giant cell, with moderate atypia ( Figures 2J-L ). Two principal cell types: small histiocyte-like cells with pale cytoplasm and round/reniform nuclei, and larger epithelioid cells with amphophilic cytoplasm, shared morphological overlap with tenosynovial giant cell tumor ( Figures 2J, K ). Figure 2K ). Focally, numerous osteoclast-like multinucleated giant cells closely resembled the giant cell tumor of bone ( Figure 2L ).
case_images: Representative IHC stains. Mononuclear tumor cells were positive for p63 (A) and SATB2 (B), but dimly positive for BRAF (E). P16 protein was strongly expressed in the spindle cells, while negative in mononuclear tumor cells (C). Positive expression of CD3 demonstrated the infiltration of scattered T lymphocytes (D). CD68 stain outlined scattered multinucleated giant cells (F).
case_images: fonc-14-1369046-g003.jpg
case_images: PMC11006978_01_fonc-14-1369046-g003.jpg
case_images: f3
case_images: Immunohistochemical stains showed that mononuclear tumor cells were positive for p63 ( Figure 3A ) and SATB2 ( Figure 3B ), but dimly positive for BRAF ( Figure 3E ). P16 protein was strongly expressed in the spindle cells, while negative in mononuclear tumor cells ( Figure 3C ). CD3 stain revealed infiltration of scattered T lymphocytes ( Figure 3D ). Scattered multinucleated giant cells were positive for CD68 ( Figure 3F ).
case_images: SLMAP-BRAF fusion was verified in the tumor. The IGV visualized map described the breakpoint site in the SLMAP-BRAF (S11:B10) fusion gene via NGS for the formalin-fixed paraffin-embedded tissue sample (A). Sequences in intron 11 of SLMAP and intron 9 of BRAF were displayed. Proper PCR primers were then designed to amplify the fusion gene by PCR (sequences marked with light blue were the DNA fragments chosen for primer blast). The PCR product was then used for sanger sequencing and DNA gel electrophoresis. Sanger sequencing result confirmed the fusion site between SLMAP and BRAF
  (B). DNA electrophoresis displayed a band slightly bigger than 250bp, which was consistent to the expected PCR product, a fragment of 267bp (C). Break-apart FISH study with green-labeled probe located 3' to BRAF and red-labeled probe located 5' to BRAF showed an aberrant pattern of an isolated 3' green signal accompanying with a normal juxtaposed red/green signal in 20% of interphase nuclei, implying an unbalanced rearrangement of BRAF gene (D). Schematic of SLMAP-BRAF fusion (E, F). In fusion gene, the exon 1-11 located 5' of SLMAP and the exon 10-19 located 3' of BRAF were retained (E). The chimeric SLMAP-BRAF protein was composed of 767 amino acid residues, preserved the kinase domain and ATP binding pocket of BRAF, while the auto-inhibitory function domains of BRAF were lost, including the N-terminal RBD (Raf-like RAS-binding domain) and C1_1 (Phorbol esters/diacylglycerol binding domain) (F).
case_images: fonc-14-1369046-g004.jpg
case_images: PMC11006978_01_fonc-14-1369046-g004.jpg
case_images: f4
case_images: Figure 4A ). Further molecular validations were successfully achieved ( Figures 4B-D ). SLMAP-BRAF Reverse primer: AGGAATCCAGTAAGCTCTTCCC). The PCR product was subsequently used for sanger sequencing and DNA gel electrophoresis. Sanger sequencing result verified SLMAP-BRAF fusion ( Figure 4B ). Figure 4C ). FISH visually exhibited an unbalanced rearrangement of BRAF ( Figure 4D ). In this fusion related chimeric gene ( Figure 4E ), the kinase domain and ATP binding pocket of BRAF were preserved, while the auto-inhibitory function domains of BRAF were lost ( Figure 4F ).