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.