The relation between the usual type of soft tissue sarcoma invading bone and the resulting bony change is well recognized. Such a lesion is commonly a fibrosarcoma of the fascial plane which grows with moderate rapidity and produces ragged absorption of adjacent bone.
The case recorded here is that of a very slowly growing fibrosarcoma of the soft parts of the forearm which first affected the bones seven years after onset of the tumor. The morphologic structure of the tumor was such that its malignant character was not suspected from examination of tissue removed at the first operation and was never definite on the basis of histologic observations alone. The unusual nature of the bone lesion resulting from the sarcoma, the great length of the history of the tumor, the difficulty encountered in making the pathologic diagnosis and the results of the conservative therapy used owing to this difficulty make