On the basis of a study of fifteen cases of parosteal osteogenic sarcoma, we concluded:
1. Parosteal osteogenic sarcoma is a recognizable clinicopathological entity which is unusual because of its low degree of malignancy. The history and roentgenographic appearance should lead the surgeon and the pathologist to suspect the diagnosis. Careful histological examination will confirm it.
2. In the past this type of tumor has commonly been believed to be a benign one, such as atypical osteochondroma or a strange recurring form of myositis ossificans. It is the authors' opinion that the lesions are usually malignant from the beginning.
3. The statement that "each neoplasm has its own . . . criteria governing benignity or malignancy"11 is again emphasized in respect to this tumor.