The use of serial bone scans in assessing response of bone metastases to systemic treatment.

The accuracy levels of serial radioisotope bone scans and conventional bone radiographs in assessing the response of bone metastases to systemic therapy were compared in 34 women with metastatic breast cancer. Each patient had measurable or evaluable nonosseous metastases, which were assessed independently of skeletal disease. The bone scan was found to be more accurate and sensitive indicator of the status of bone metastases than the radiograph. The bone scan correlated well with response of soft tissue or visceral disease, while the results of repeated bone radiographs were frequently misleading. With use of a digital model, it was possible to accurately measure the area of skeletal involvement of the bone scan, and from this derive quantitative criteria for response in bone metastases analogous to response criteria currently in use for soft tissue and visceral disease. It is suggested that serial quantitative bone scans be done, in preference to radiographs, to assess the response of bone metastases to systemic therapy.