Lingual liposarcoma transitioning from an infiltrative lipoma in a dog.

Lingual neoplasms comprise approximately 2-4 % of canine oropharyngeal tumours, with liposarcomas being particularly rare and typically arising in the subcutis of the extremities and trunk. This report describes a 5-year-old spayed female Bedlington Terrier that presented with a ruptured lingual mass with muscular invasion, for which glossectomy was performed. Histopathological examination revealed a neoplastic proliferation of well-differentiated adipocytes that infiltrated the skeletal muscle layer. The deeper portion of the mass had dedifferentiation of adipocytes and malignant transformation into liposarcoma. The dedifferentiated neoplastic spindle cells contained cytoplasmic lipid vacuoles that stained positively with Oil Red O and had marked pleomorphism and elevated mitotic activity. Immunohistochemically, the neoplastic cells were positive for S100 and negative for CD34. While prior studies have suggested that liposarcomas do not originate from the malignant transformation of lipomas, the findings in this case support the possibility of infiltrative lipoma undergoing malignant transformation into a dedifferentiated and aggressive liposarcoma. This case underscores the potential for benign lipomatous lesions to evolve into their malignant counterparts under certain pathological conditions.