Bone scintigraphy for metastasis detection in canine osteosarcoma

The purpose of this study was to assess the usefulness of serial bone scintigraphy in the detection of skeletal and extraskeletal metastases in dogs with appendicular osteosarcoma. Twenty-six dogs with primary, appendicular osteosarcoma were entered into a limb-sparing protocol. Bone scintigraphy was performed upon presentation, after neoadjuvant therapy but prior to surgery and at selective intervals after limb-sparing surgery to evaluate for the presence of metastasis. Thoracic radiographs, and radiographs of other sites, were also made at the time of each bone scan. All dogs had a complete necropsy. No dog had bone or lung metastases detected prior to treatment. The bone scans, medical records, and radiographs of each dog were reviewed retrospectively. All but one dog developed metastatic disease. Bone metastatic sites were confirmed at necropsy in 12 of the 26 dogs. Seven of these 12 dogs had bone metastatic sites which were not producing clinical signs, i.e. an occult metastasis. In five of the seven dogs, the occult site was the first metastatic site detected. Extraskeletal metastases were identified scintigraphically in six of the 26 dogs, but these were clinically apparent prior to bone scintigraphy in each dog. Suspected malignant scintigraphic lesions were proven benign in six dogs. In five dogs with malignant bone lesions at necropsy the last bone scan prior to euthanasia was normal. The time interval between scintigraphy and necropsy was variable in these five dogs. All dogs without bone metastases at necropsy had normal bone scans. This study validates the usefulness of bone scintigraphy for detection of occult bone metastasis and improved ability for tumor staging in dogs with appendicular osteosarcoma