Tumor heterogeneity in osteosarcoma as identified by flow cytometry

Measurements of the cellular DNA content by flow cytometry were carried out in 25 untreated osteosarcomas to identify the frequency of DNA aneuploidies and heterogeneous DNA stemlines in relation to histopathology. Analyzing multiple specimens from each single tumor (2-16; median, 4), highly malignant osteosarcomas were found to express DNA aneuploidies in 18 of 21 cases (86%) with multiple aneuploid DNA stemlines in 10 cases (48%). In three paraosteal osteosarcomas, no DNA aneuploidy was detected and a significantly lower proportion of cells in S-phase was observed as compared to the highly malignant osteosarcomas (mean 8.6% vs. 18.8%; P less than 0.05). Like in the paraosteal osteosarcomas, no DNA aneuploidy and a low fraction of cells in S-phase was found in the predominant cell population of one of the very rare sclerosing small cell osteosarcomas, which also revealed a second DNA stemline with a DNA index of 2.0. These results demonstrate a high degree of DNA stemline heterogeneity in highly malignant osteosarcomas. The data emphasize the usefulness of DNA measurements for the characterization of bone tumors and indicate the possibility of discriminating highly malignant from low-grade osteosarcomas.