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 masse s of the maxilla and mandible were reviewed. Most of the dogs had exte nsive clinical histories and had had previous biopsies of the affected regions, from which specimens were often interpreted as benign fibrou s connective tissue. The most common breed represented was Golden Retr iever (13/25 dogs, 52%). Skull radiographs were evaluated for 22 dogs, and 16 dogs (72%) had evidence of bone lysis. At admission, none of t he dogs had radiographic evidence of pulmonary metastasis. On subseque nt examinations and necropsy, prevalence of pulmonary metastasis was 1 2% (3/25 dogs) and of regional lymph node metastasis, 20% (5/25 dogs). Histologic appearance of all specimens was similar and was characteri zed by proliferation of fibrous connective tissue, with moderate to lo w cellularity, that aggressively infiltrated adjacent normal tissue. T reatment modalities varied considerably. Surgical excision in combinat ion with radiation therapy, surgery alone, radiation therapy alone, an d radiation therapy wed adjunctly with localized hyperthermia prolonge d survival times in some dogs. The clinical signs, tumor behavior, and histologic characteristics of these lesions were distinctive from tho se in previously described oral fibrosarcomas in dogs. Comparatively, these tumors most closely resembled aggressive fibromatoses in human b eings in regard to clinical signs, local invasive behavior, and histol ogic appearance, but differed in the prevalence of metastasis.