Four Cases of the Melanotic Variant of Malignant Nerve Sheath Tumour: a Rare, Aggressive Neoplasm in Young Dogs with a Predilection for the Spinal Cord

Assessment of SOX10 expression in 437 canine neoplasms of different embryologic origins

Several members of the SRY-related HMG-box (SOX) protein family are implicated in tumorigenesis, metastasis, and regulation of the tumor microenvironment. SOX10, which is involved in neural crest cell migration and differentiation, has long been recognized a sensitive and specific immunohistochemical (IHC) marker in the diagnosis of melanoma in humans. However, expression of SOX10 in other tumor types has infrequently been evaluated in humans until recently and has not been thoroughly investigated in the dog. Our aim was to characterize the expression of SOX10 in canine neoplasms to objectively assess its value as a diagnostic IHC marker. Immunohistochemistry for SOX10 was performed on 437 archived, formalin-fixed paraffin-embedded tissues from representative canine neoplasms of ectodermal (15 tumor types), mesodermal (13 tumor types), endodermal (8 tumor types), and mixed/unknown (7 tumor types) embryologic origin. Oral and cutaneous tumors of melanocytic origin were used as positive controls. Intense SOX10 immunolabeling was observed in most tumors of ectodermal origin, including consistent expression in mammary carcinomas, and gliomas. Embryonal and hair follicle neoplasms inconsistently exhibited strong nuclear immunolabeling. Oral fibrosarcomas and undifferentiated oral sarcomas both inconsistently exhibited moderate to strong nuclear immunolabeling. Neoplasms of mesodermal and endodermal origin lacked immunolabeling. Salivary carcinomas, representing an unknown/mixed embryologic origin, were strongly labeled. SOX10 expression is not limited to melanomas, but is expressed by canine tumors of diverse tissues and embryologic derivation. Importantly, expression of SOX10 by a subset of oral sarcomas impairs its value as a marker for spindle cell oral melanomas.

Case report: MRI and CT imaging features of a melanocytic tumour affecting a cervical vertebra in an adult dog, and review of differential diagnosis for T1W-hyperintense lesions

A 7-year-old Lhasa Apso presented with a history of left thoracic limb lameness and neck pain. Magnetic resonance imaging revealed a well-defined, extradural lesion that was hyperintense on T1-weighted (T1W) images and isointense on T2-weighted (T2W) images and T2* images located at the left lamina of the C4 vertebra. Computed tomography showed an isoattenuating and contrast-enhancing mass centered on the left C4 vertebral lamina with associated osteolysis. The mass was surgically debulked, and histopathology revealed a malignant melanocytic tumour. The patient recovered completely and received radiotherapy and three doses of the melanoma vaccine as adjunctive treatment. Eighteen months following treatment, the patient presented with neck pain again, but further investigations were declined at this stage, and the patient was euthanised. To the author's knowledge, this is the first case report describing the imaging characteristics of a cervical extradural melanocytic tumour in a dog. This case illustrates the MRI and CT imaging features and treatment of a canine melanocytic tumour of the cervical vertebrae.

Metastatic Multifocal Malignant Peripheral Nerve Sheath Tumour in the Cervicothoracic Spinal Cord of a Dog Initially Mimicking Meningomyelitis

A nine year old cross-breed dog was presented with a two week history of ambulatory tetraparesis and proprioceptive ataxia affecting all four limbs. Meningomyelitis of Unknown Origin (MUO) was presumptively diagnosed based on the magnetic resonance imaging (MRI) findings and cerebrospinal fluid (CSF) analysis. The dog received a tapering dose of glucocorticoids and cyclosporine, showing significant improvement and the stabilization of the clinical signs for seven months. After this period, the dog showed an acute clinical deterioration and a follow-up MRI revealed new multiple lesions affecting different spinal nerve roots along the cervicothoracic spinal cord. Following euthanasia, a final diagnose of multiple malignant peripheral nerve sheath tumors (MPNSTs) was made based on the histopathological examination. MPNSTs can affect the cranial nerves, spinal nerves or the associated nerve roots at any location and can lead to secondary spinal cord compression. The aim of the present case report is to describe the clinical presentation and atypical MRI findings of a dog with histologically confirmed multiple MPNSTs. According to the reviewed literature, this is the first reported case of simultaneous MPNSTs in the cervicothoracic spinal cord of a dog.

Histopathological and Immunohistochemical Evaluation of Canine Nerve Sheath Tumors and Proposal for an Updated Classification

Nerve sheath tumors are a group of tumors originating from Schwann cells, fibroblasts, and perineurial cells. In veterinary pathology, the terminology for nerve sheath tumors remains inconsistent, and many pathologists follow the human classification of such tumors in practice. Immunohistochemistry plays an important role in the diagnosis of nerve sheath tumors, but specific immunohistochemical and molecular biomarkers are lacking. In our study, we histopathologically reevaluated 79 canine nerve sheath tumors and assessed their reactivity for the immunohistochemical markers Sox10, claudin-1, GFAP, CNPase, and Ki-67. Based on the results, we classified the tumors according to the most recent human classification. Twelve cases were diagnosed as benign nerve sheath tumors, including six neurofibromas, three nerve sheath myxomas, two hybrid nerve sheath tumors (perineurioma/neurofibroma and perineurioma/schwannoma), and one schwannoma. Sixty-seven tumors were malignant nerve sheath tumors, including fifty-six conventional, four perineural, one epithelioid malignant nerve sheath tumor, and six malignant nerve sheath tumors with divergent differentiation. We believe that with the application of the proposed panel, an updated classification of canine nerve sheath tumors could largely follow the recent human WHO classification of tumors of the cranial and paraspinal nerves, but prospective studies would be needed to assess its prognostic value.