Tumors develop when cells in the body grow uncontrollably. Finding a tumor on your dog can be very frightening, but they are not always detrimental — some are benign, while others are malignant.

On the basis of the appearance of sections of the mass stained with hematoxylin and eosin, we made a diagnosis of a spindle cell tumor (Fig. 2). Such tumors are a highly heterogeneous group that ...