Relationship between histologic grade and cytofluorometric cellular DNA and RNA content in primary bone tumors

The diagnosis and grading of bone tumors remains a challenging problem. We studied the relationship between histologic grade and cytofluorometric cell ular DNA and RNA content in 108 primary bone tumors. The data included DNA ploidy, mean DNA content (MDC), S-phase fraction (SPF), mean RNA content (M RC) and RNA/DNA ratio (RDR; MRC/MDC) which represents the RNA content norma lized for the DNA content. Benign tumors had a diploid stem line with low M DC (mean;1.04), low SPF (0.9), high MRC (2.41) and high RDR (2.31). Giant c ell tumors of bone, which ar e locally agressive benign tumors, showed dipl oidy with relatively higher MDC (1.07, p <0.01) and SPF (2.6 p <0.01) and l ower MRC (1.82, p <0.01) and RDR (1.69 p <0.01). Similar results were obtai ned in low-grade sarcomas. In high-grade sar comas, the data depended on th e histologic findings. Pleomorphic sarcomas such as osteosarcomas revealed aneuploidy with remarkably higher MDC (1.70 in osteosarcomas, p <0.01) and SPF (6.5, p <0.01), but lower RDR (1.70, p <0.02). In contrast, small cell sarcomas, such as Ewing's sal comas, showed diploidy with low MDC (1.11 in Ewing's sarcomas, N.S.) and SPF (2.5, p <0.01) and extremely low RDR (1.34, p <0.01). The RDR value was higher in well-differentiated tumors than in p rimitive tumors, rendering it useful in grading bone tumors with a diploid stem fine. By combining the RDR value with the MDC value 96 % of diploid sa rcomas could be distinguished from benign tumors. These results indicate th at cellular DNA and RNA content analysis may be of value in assessing the m alignant potential of diploid as well as aneuploid bone sarcomas.