The diagnostic utility of SOX11 Immunohistochemical expression in malignant peripheral nerve sheath tumors and their potential mimickers.

Malignant peripheral nerve sheath tumor (MPNST) comprises 5-10 % of all soft tissue sarcomas, and their diagnosis may be challenging given the absence of robust immunohistochemical and molecular signatures. SOX11 expression has previously been shown to be present in a small subset of MPNST. In the present study, we evaluated a group of MPNST for SOX11 expression by immunohistochemistry. We similarly assessed a group of benign and malignant spindle cell tumors that are in the differential diagnosis of MPNST, to more expansively establish the specificity of the antibody. In total, 59 MPNSTs, 27 synovial sarcomas, 19 leiomyosarcomas, 19 rhabdomyosarcomas, 19 solitary fibrous tumors, 4 clear cell sarcomas of soft tissue, 19 malignant melanomas, 22 schwannomas (11 classical, 11 cellular), 9 neurofibromas (4 plexiform, 2 atypical, and 3 classical) and 9 nodular fasciitis were included. SOX11 was strongly positive in 41 of 59 MPNSTs (67 %), 16 of 27 synovial sarcomas (59 %), 11 of 19 rhabdomyosarcomas (58 %), 1 of 4 clear cell sarcomas (25 %), and 5 of 9 nodular fasciitis (56 %). In contrast, neurofibromas(n=11)), schwannomas (n=22), leiomyosarcomas (n=22), and solitary fibrous tumors (n=19) were either negative or showed only weak and focal expression for SOX11. The sensitivity and specificity of strong SOX11 expression in differentiating MPNST from its mimickers were 70 % and 73 %, respectively. In conclusion, the diagnostic utility of SOX11 expression for MPNST is limited, but the absence of significant SOX11 expression in benign/atypical nerve sheath tumors is interesting and deserves further investigation.