The nuclear DNA content of 38 malignant and 25 benign bone tumours was measured by flow cytometry. The specimens were taken either from biopsies or from surgical specimens. Seventeen of 26 primary malignant bone tumours were aneuploid, 15 had a single aneuploid DNA content, and 2 had a biclonal abnormality. Thirteen of 15 osteosarcomas were aneuploid, but only 2 of 6 chondrosarcomas showed an aneuploid DNA content. Six of 12 metastatic malignant bone tumours were also aneuploid. All 25 benign tumours had a diploid DNA content. Cell cycle analysis showed that the proportion of cells in S-and G2M-phases was higher in the malignant compared to benign tumours, indicating a higher proliferative activity. The increase was statistically significant (p < 0.05) both in diploid and in aneuploid tumours. Among five tumours studied after chemotherapy, four displayed a marked hyperdiploid abnormality. Aneuploidy and high proliferative activity both were highly associated with malignant bone tumours, suggesting that DNA flow cytometry may be an adjunct in the assessment of malignancy of bone tumours.Key terms: DNA neoplasm, flow cytometry, bone neoplasms, aneuploidyThe benign or malignant nature of bone tumours is usually assessed by the clinical presentation, radiological and laboratory findings, and above all by the histologic examination of biopsies. This provides an estimate of the growth pattern, cellularity, number of mitoses, nuclear pleomorphy, etc. The evaluation requires experience, and because bone tumours are relatively rare, expert consultation may be required.For some years it has been known that malignant tumours contain cells with an abnormal nuclear DNA content (2,11,15,18,(20)(21)(22)24), and this has been confirmed by flow cytometry (FCM) (1,3-6,8-10), 12-14,16,17,19-23,25,29,31,34-36). There has been limited investigation of the DNA content of bone tumour cells. Most studies are on cartilage tumours (1,20-22,241. Kreicbergs has also studied cells from some other bone tumours (23). In addition the DNA content of myeloma cells has been measured (4,6,9). In all these studies aneuploidy has been attributed to tumour malignancy.The aim of the present investigation was to determine whether measurements of nuclear DNA content by FCM could be of value for the assessment of the malignancy of bone tumours.sinki University Central Hospital. All patients were suspected of having bone tumours. More than one specimen on different occasions was obtained from 11 patients. Thus a total of 75 specimens were obtained, either by routine biopsy or at the time of the sur 'cal procedure. The specimens measured about 1 cm? and they were immediately immersed in 0.9% saline.Tissue specimens were minced within 1 h and teased apart in phosphate buffered saline. The cell suspension was filtered through cotton wool and centrifuged for 7 min at lOOg, then resuspended in a buffer solution containing 50 pg/ml ethidium bromide (Sigma Chemical Co, St. Louis, MO) in 0.3% Nonidet P-40 (BDH-chemicals, Poole, England), lOmM Tris, and 2 mM EDTA ...