Growth rate analysis of lung metastases from histologically benign giant cell tumor of bone.

A growth rate analysis of lung metastases of benign giant cell tumor (GCT) of bone, histologically indistinguishable from the primary benign tumor, is presented. The doubling time (DT) was 186 days in the first 13 months of growth, and 465 days in the last 4 months. These DTs are much longer than DT of lung metastases of any other tumors, and have a good correlation with a long survival time. Backward extrapolation showed that the lung metastases began to develop years before the primary tumor was diagnosed and treated. If this can be confirmed in a larger number of patients, it could be concluded that there will be no indication for amputation as a treatment for benign GCT whether or not lung metastases are present. The growth rate analysis supports the concept that these metastases might represent a benign process, and as such are a unique histologic and clinical phenomenon.