Discordance of sclerosing skeletal secondaries between sequential scintigraphy and radiographs

Regression in metastatic lesions as seen on a bone scan may be accompanied by increasing sclerosis radiographically. There are two possible causes for interval radiographic sclerosis: progressive osteoblastic tumor deposition or the healing process itself. The presence of active neoplasia can better be determined in sclerotic lesions by the bone scan which demonstrates the tumor-induced new bone formation, as compared to radiographs which show the more unpredictable results of new bone formation plus the reparative process. Two cases are presented to illustrate the importance of bone scanning in determining whether sclerosis indicates disease progression or regression.