Spindle Cell Variant of Cutaneous Squamous Cell Carcinoma in a ۹-Year-Old German Shepherd: A Case Report

Introduction: Skin tumors are a common presentation in canine medicine and surgery and account for approximately ۴۰% of all tumors in dogs. Squamous cell carcinoma (SCC) represents about ۲% of all canine skin tumors, and several histological variants of SCC have been described. Among them, the spindle cell SCC is a rare variant and may be diagnostically challenging due to striking resemblance to other malignant neoplasms. Case Presentation: A ۹-years-old female German Shepherd dog was referred to Labra Veterinary Laboratory for diagnosis of multiple nodules in the ventral abdominal region. Lesions were firm, ulcerated, and slowly progressive in evolution. Cytology revealed abundant spindle-shaped neoplastic cells that were organized into loose aggregates. Marked neutrophilic inflammation was also noted. Cytologic interpretation of the lesions raised the possibility of malignant mesenchymal tumor.  Histopathology of excisional biopsy samples revealed a highly cellular lesion that was composed of invasive sheets and fascicles of pleomorphic spindle cells with eosinophilic cytoplasm, prominent nucleoli, and frequent mitotic figures. Areas of keratinization were rare and no melanin pigment was identified. The presumptive pathologic diagnoses included amelanotic malignant melanoma and spindle cell SCC. To further characterize the neoplastic cells, immunohistochemistry was performed and tumor cells were negative for S۱۰۰ protein. S۱۰۰ is a neural marker, therefore negativity of it rules out the diagnosis of amelanotic melanoma, and confirming the diagnosis of spindle cell variant of SCC. Conclusion: Cutaneous SCC is a common presentation in dogs and well differentiated lesions show distinct histologic characteristics. However, there are some uncommon variants of SCC, such as spindle cell type, that may be easily confused with other malignant neoplasms, mostly amelanotic malignant melanoma. In the present case, cytologic impression was not definitive, and the spindle cell SCC mimicked a mesenchymal neoplasm. A misdiagnosis at the cytologic level may lead to inadequate treatment plan and more importantly, an inappropriate prognosis. This case serves as a reminder that unusual variants of common lesions, and uncommon lesions that are not often encountered in routine practice can cause diagnostic challenge. Pathologists and clinicians should be aware of these entities to prevent incorrect diagnosis.

کلیدواژه ها:

Dog ، German Shepherd ، Spindle cell squamous cell carcinoma ، Amelanotic melanoma ، Immunohistochemistry