Malignant histiocytosis in a Bernese mountain dog presenting as a mandibular mass.

A Bernese mountain dog was evaluated because of a gingival mass, multiple abdominal masses, and a pulmonary mass. Malignant histiocytosis was diagnosed based on cytological examination of splenic and bone marrow aspirates and histological examination of a bone marrow biopsy and the gingival mass. The case demonstrates that malignant histiocytosis is difficult to diagnose due to the variety of histiocytic disorders.