Multiple distinct malignancies in dogs: 53 cases.

Despite the clinical recognition of multiple distinct types of neoplasia in individual dogs, a detailed description of such cases has not recently been published. Canine oncology cases that were diagnosed with multiple, confirmed, distinct malignancies were prospectively collected for analysis. Approximately 3% of 1722 dogs that were presented to the oncology service at the Colorado State University Veterinary Medical Center were diagnosed with multiple distinct primary tumors. No significant breed or sex predisposition was apparent. Dogs with mast cell tumor, malignant melanoma, and thyroid carcinoma were significantly overrepresented and thus more likely to be diagnosed with multiple tumor types. These findings emphasize the importance of thorough, whole-body evaluation for dogs presented with mast cell tumor, malignant melanoma, and thyroid carcinoma. Furthermore, because approximately 33% of dogs that were presented with thyroid tumors were found to have additional distinct tumors, complete staging is justified in all dogs presented with thyroid tumors.