Histologically low-grade, yet biologically high-grade, fibrosarcomas of the mandible and maxilla in dogs: 25 cases (1982-1991).

Medical records of 25 dogs with histologically low-grade fibrous masses of the maxilla and mandible were reviewed. Most of the dogs had extensive clinical histories and had had previous biopsies of the affected regions, from which specimens were often interpreted as benign fibrous connective tissue. The most common breed represented was Golden Retriever (13/25 dogs, 52%). Skull radiographs were evaluated for 22 dogs, and 16 dogs (72%) had evidence of bone lysis. At admission, none of the dogs had radiographic evidence of pulmonary metastasis. On subsequent examinations and necropsy, prevalence of pulmonary metastasis was 12% (3/25 dogs) and of regional lymph node metastasis, 20% (5/25 dogs). Histologic appearance of all specimens was similar and was characterized by proliferation of fibrous connective tissue, with moderate to low cellularity, that aggressively infiltrated adjacent normal tissue. Treatment modalities varied considerably. Surgical excision in combination with radiation therapy, surgery alone, radiation therapy alone, and radiation therapy used adjunctly with localized hyperthermia prolonged survival times in some dogs. The clinical signs, tumor behavior, and histologic characteristics of these lesions were distinctive from those in previously described oral fibrosarcomas in dogs. Comparatively, these tumors most closely resembled aggressive fibromatoses in human beings in regard to clinical signs, local invasive behavior, and histologic appearance, but differed in the prevalence of metastasis.