The assessment of response to therapy of bone metastases in breast cancer.

Serial bone scans, x-rays and records of bone pain were reviewed in order to determine the relative contributions of these parameters in the assessment of response of bone metastases to treatment. Twenty-seven patients with abnormal bone scans due to metastatic breast cancer were studied. Ten of the patients showed an early temporary flare on bone scan including five with apparent new lesions. Confirmation that such new lesions did not denote progressive disease was provided by subsequent improvement in symptoms and reduction in intensity and number of lesions on a follow-up bone scan, without any change in systemic therapy. Serial x-rays were found to be unreliable as a sole method for assessing response to therapy or disease progression, as in only seven of the 27 patients could a definitive radiological assessment of response be made. In only one patient did x-rays improve the accuracy of the scan by distinguishing between a healing flare and progressive disease. In contrast, this distinction was made in seven of the 10 patients on the basis of improvement in bone pain at the time of the flare. The other 3 patients had no bone pain prior to therapy or at the time of the flare. Tentative response criteria incorporating bone scan, x-ray and symptoms are suggested. The criteria incorporate recognition of the fact that new lesions appearing on a bone scan within six months of initiation of therapy may comprise part of a healing flare response.