SUMMARY
Malignant peripheral nerve sheath tumor is rare and rarely reported in dogs. The term neurofibroma/sarcoma is classically used when the tumor is composed of Schawann and perineural cells. This work describes the clinical, histopathological, and immunohistochemical case of a subcutaneous malignant peripheral nerve sheath tumor, most likely a malignant neurofibroma located in the pelvic member of a Rottweiler dog. Histopathological features and immunohistochemical analysis corroborated the diagnosis, showing positivity for S-100 protein, vimentin, and CD57, and was useful to distinguish this type of neoplasm from other malignancies of similar morphologies.