Rapid Malignant Transformation of a Biopsy Proven Sporadic Soft Tissue Schwannoma to Spindle Cell MPNST With <i>TP53</i> Mutation as an Early Event

Malignant peripheral nerve sheath tumors (MPNSTs) primarily originate from the neurofibromatosis 1 (NF1)- associated and/or sporadic neurofibromas. Reports of malignant transformation from a sporadic soft tissue schwannoma are rare. In most tumors documented in this context so far, the malignant component is an epithelioid MPNST with a strong and diffuse S100 positivity. We present a patient diagnosed with a sporadic soft tissue schwannoma on core biopsy, which underwent rapid malignant transformation to a spindle cell type MPNST. Somatic tumor profiling of the excision specimen revealed <i>NF2</i> loss, <i>TP53</i>, <i>NRAS</i>, and subclonal <i>RICTOR</i> gene mutations. A retrospective immunohistochemical stain for p53 on the core biopsy demonstrated an aberrant staining pattern, indicating an early effect of <i>TP53</i> in the process of malignant transformation.