Skeletal metastasis as the initial clinical manifestation of metastatic carcinoma in 19 dogs.

Although the skeleton represents a potentially important target for the metastatic spread of carcinoma, the clinicopathologic features of skeletal metastases in dogs have not been documented extensively. In particular, no reports have focused on dogs in which skeletal metastasis was the initial clinical manifestation of their malignancy. Medical records were reviewed for dogs with skeletal carcinoma and cases were subdivided into 2 groups based upon the temporal relationship between the diagnosis of carcinoma and recognition of skeletal metastases. In 19 of 24 (79%) dogs, skeletal metastasis was the initial clinical manifestation of malignancy, and these dogs were studied in detail. Most affected dogs were elderly and weighted less than 25 kg. Thirty-six skeletal lesions were identified in 19 dogs. Skeletal metastases occurred most frequently in the axial skeleton and proximal long bones. Only 4 of 36 (11%) skeletal carcinomas occurred distal to the elbow or stifle. Mammary gland, prostate, and urinary bladder were the most common primary sites. In 11 of 19 (58%), dogs, the primary tumor could not be determined, and in 6 of these dogs, the primary tumor could not be identified despite complete postmortem evaluation. Physical examination and abdominal ultrasonography were most valuable in detecting the primary tumor. Although biopsy or fine-needle aspirate of skeletal lesions was essential in the diagnosis of skeletal carcinoma, these procedures did not yield definitive information on the primary tumor site. This report documents that the majority of skeletal metastases are diagnosed in dogs without a previous diagnosis of carcinoma. Detection of the primary tumor in these cases may be challenging, and skeletal metastases are frequently attributable to carcinoma of unknown origin.