Primary malignancy, secondary malignancy and semimalignancy of bone tumors.

1. Bone tumors in contrast to tumors in soft tissue, show a wide variety of clinical behavior qualified by the expressions semimalignancy, low grade of malignancy, sarcomatous degeneration and primarily benign bone tumors and bone lesions. 2. The term semimalignancy is characterized by local invasive and destructive tumor growth with a tendency to recur locally but no hematogeneous spreading. Semimalignancy requires wide en-bloc resection of amputation. 3. The term low grade malignancy is used to describe a tumor of very slow growth and with very late metastasis. Low-grade malignancy requires resection with careful preservation of functional structures. 4. The term secondary malignancy means the sarcomatous degeneration of a primarily benign lesion or bone tumor. This transformation is enhanced by irradiation and probably by acceleration of the normal turnover of bone tissue. In Paget's disease sarcomatous degeneration is to be expected in 2 percent of cases and in fibrous dysplasia in 0.5 percent of cases. 5. Sarcomatous degeneration of bone infarcts is rare, but an increase is to be expected due to an increased frequency of bone infarcts caused by long-term treatment with cortisone. 6. Primary bone tumors and recurrences show the same structure and cytology. In a minority of cases the recurrences are less differentiated; in a very few cases the recurrences are more highly differentiated and have a better prognosis than the initial lesion.