Synovial sarcomas may show focal nuclear palisading similar to that seen in the neural tumors. This image is higher magnification of the previous slide. About 30% of synovial sarcomas are S-100 protein positive that may add to the confusion. Synovial sarcoma vs MPNST: Malignant peripheral nerve sheath tumor may be seen clearly originating from a nerve or arise from a preexisting neurofibroma or be seen in patients with neurofibromatosis 1. The spindle tumor cells of MPNST appear wavy or buckled. Immunohistochemically, MPNSTs are positive for S-100 (at least focally, in two-thirds of cases) and HMGA2 and negative for CK7 and CK19. Synovial sarcomas are S-100 positive in one-third of cases, positive for CK7 and CK19, and negative for HMGA2. Rare examples of synovial sarcoma arising from peripheral nerves have been reported.