Figure 1. Novel BRAF-fusions in histiocytic neoplasms mediate oncogenicity via activation of MAPK/PI3K/mTOR pathway: Malignant histiocytic neoplasm with histiocytic and Langerhans cell sarcoma phenotypes with novel MTAP-BRAF fusion, and atypical juvenile xanthogranuloma family lesion with novel MS4A6A-BRAF fusion.
A-F. Case 1 Malignant histiocytic neoplasm with large, pleomorphic cells (A-B) and areas of necrosis (*). Immunohistochemistry with CD163 (C), CD1a (D) and Langerin (E) in a subset of lesional cells. Ki-67 proliferation index (F) was elevated up to 20%, including atypical large cells (F). (Original magnification A. 200x, B, 4000x, C-E. 1000x, F. 200x). BRAF VE1 immunostain was negative (not shown).G-M. Case 2 atypical juvenile xanthogranuloma (JXG) family neoplasm with bland histiocytes (G-H) and a rare mitosis (H, center). Immunohistochemistry with Factor XIIIa (I) was strongly and diffusely positive. The Ki-67 proliferation index was variable, as high as 40% (J-K) in one core biopsy and as low as 10% in other core (L-M) taken at the same time and accounting for inflammation, which was low in both core biopsies. (Original magnification: G. 100x, H. 1000x, I. 200x, J. 100x, K. 1000x, L. 100x, M. 1000x). The BRAF VE1 immunostain was negative (not shown). N-P. Case 2 with JXG: Imaging at diagnosis revealed a crescentic enhancing soft tissue mass by magnetic resonance imaging wrapping around the calcaneus, deep to the Achilles tendon (N, arrows) and positron emission tomography (PET) scanning revealed abnormal signal in the ankle (primary), knee, inguinal region and chest (O). Following 9 of 12 cycles of clofarabine, PET scan revealed resolution of disseminated disease and shrinkage of the primary ankle tumor. Q . Structure of novel BRAF-fusions in histiocytic neoplasms. MTAP-BRAF: MTAP exons 1-7 encode phosphate binding sites, trimerization site at Trp189 residue, and substrate binding site, and BRAF exons 9-18 encode the tyrosine kinase domain. MS4A6A-BRAF: MS4A6A exons 1-6 encode 4 transmembrane helical regions, and BRAF exons 11-18 encode the tyrosine kinase domain. R. Soft agar assay using NIH3T3 cells stably expressing BRAF-fusions. Error bars represent SEM, n=5, ***p-value<0.001 compared with control conditions.S. Western blot analysis of MAPK and PI3K/mTOR pathway proteins in NIH3T3 cells stably expressing BRAF-fusions. ‘p-‘ and ‘t-‘ represent phosphorylated and total versions of protein, respectively.