Proliferative potential of canine oral epulides and malignant neoplasms assessed by bromodeoxyuridine labeling.

The proliferative potential of canine oral lesions, including epulides, squamous cell carcinomas, a malignant melanoma, and a fibrosarcoma, was examined using a monoclonal antibody to bromodeoxyuridine (BrdU). Twenty-three dogs with oral masses were administered BrdU intravenously at a dose of 8 mg/kg 1 hour before surgery, and the BrdU labeling index (LI) of each lesion was determined immunohistochemically. The average BrdU LIs for the main proliferating elements in the fibromatous epulis (4 cases), ossifying epulis (2 cases), and acanthomatous epulis (10 cases) were 4.9, 3.0, and 8.8%, respectively. The squamous cell carcinomas (5 cases) had an average LI of 15.9%, and the LIs of the malignant melanoma and fibrosarcoma were 7.5 and 10.3%, respectively. All cases of acanthomatous epulides and squamous cell carcinoma treated with simple marginal surgical resection recurred within a short time. The higher LIs in the acanthomatous epulides, squamous cell carcinomas, and fibrosarcoma correlate well with their poor prognoses, reflected by rapid growth and frequent recurrence. Acanthomatous epulis is clearly distinguished from other epulides by its aggressive clinical behavior and high proliferative potential, which is equivalent to that of malignant tumors, despite a lack of cell atypia. The BrdU LI is a useful marker for evaluating the proliferative potential and prognosis of canine oral tumors.