Case 180511-2

Fourteen-year-old, male, domestic shorthair cat

The owners noted an oral mass approximately one month prior to presentation. The owners declined a workup of the mass, opting for palliative care with prednisone and buprenorphine. The mass continued to grow, eventually crossing the mandibular midline, and the patient was euthanized due to quality of life concerns.

Expanding the left side of the mandible is a 6 x 5 x 3 cm, hard, smooth, pale tan mass that spans the entire length of the mandible. The caudal margin of the mass is the left temporomandibular joint, which grossly appears unaffected. Two teeth embedded within the caudal aspect of the mass (presumed molars) are easily moveable. The mass focally spans midline, extending to and invading the rostral third of the right mandible.

One section of mandible is examined, which includes mandibular foramen, salivary gland and oral mucosa. The superficial two-thirds of the bone are composed of dense, variably-sized, poorly organized, anastomosing, bony trabeculae that occasionally have scalloped or irregularly contoured edges. The trabecular medullary spaces are lined by cords and nests of polygonal cells supported by a fine fibrovascular stroma. Cells have distinct cell borders, often with prominent cell junctions, and a scant to moderate amount of brightly eosinophilic, fibrillar cytoplasm. Cell nuclei are hyperchromatic with indistinct nucleoli. These cells frequently undergo abrupt keratinization, forming concentric lamellae and irregularly-shaped accumulations of keratin. The keratin is admixed with necrotic debris and spicules of necrotic bone, characterized by hyper-eosinophilia and acellular lacunae. Cells are additionally characterized by frequent single-cell necrosis. Anisocytosis and anisokaryosis are moderate. There are two mitotic figures per ten, 400x fields.

N/A

Mandibular squamous-cell carcinoma with osteogenesis

This slide includes gingiva and salivary gland, allowing the viewer to confirm the location of the mass. Squamous-cell carcinomas (SCCs) are the most common oral neoplasms of cats, and they most often develop in the mandibular, maxillary and sublingual regions. There is no known cause of feline oral SCCs; no association has been made between these tumors and environmental tobacco smoke, papillomavirus, feline leukemia virus, or feline immunodeficiency virus. Feline oral SCCs rarely metastasize but are highly invasive. Bone lysis is frequently observed on radiographs and was a significant feature in this case. The viewer must recognize that the spicules and trabeculae of woven bone represent tumor-induced osteogenesis and are not normal mandibular bone.

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