THE EXPRESSION PATTERN OF CONTRACTILE AND INTERMEDIATE FILAMENT PROTEINS IN DEVELOPING SKELETAL-MUSCLE AND RHABDOMYOSARCOMA OF CHILDHOOD - DIAGNOSTIC AND PROGNOSTIC UTILITY

In order to investigate whether rhabdomyosarcoma (RMS) can be related to equivalent stages of skeletal muscle development, muscle tissue of 21 human foetuses and 112 primary RMSs were characterized immunohistoc hemically using antibodies directed against vimentin, desmin, muscle-s pecific actin (HHF35), sarcomeric actin (sr-actin), smooth muscle acti n (sm-actin), and troponin-T. During fetal skeletal muscle development , all myotubes/fibres of the first and second generations expressed de smin, HHF35, and sr-actin. Vimentin was almost exclusively present in immature primary and secondary myotubes/fibres. Troponin-T was express ed in immature myotubes/fibres of the first and second generations as well as mature fibres of the second generation. Sm-actin was never exp ressed. Vimentin was expressed in 96 per cent of primary and 98 per ce nt of relapsed RMS; HHF35 in 96 and 98 per cent, respectively; desmin in 95 and 100 per cent; troponin-T in 82 and 75 per cent; sr-actin in 71 and 86 per cent; and sm-actin in 13 and 17 per cent. The proportion of RMS cells reacting with vimentin, HHF35, and desmin was consistent ly higher than those expressing sr-actin and troponin-T. Neither the s hape nor size of neoplastic RMS cells nor the histopathological types were related to the expression pattern of the investigated markers. RM S with aberrant expression of two or more markers predicted a worse pr ognosis than RMS in which at most one marker was aberrantly expressed (25 per cent and 54 per cent 10-year survival, P=0.01). These results demonstrate that HHF35, desmin, sr-actin, and troponin-T have the pote ntial to confirm the commitment of the tumours to the myogenic pathway which supports the diagnosis of RMS. However, it was impossible to re late RMS to equivalent stages of skeletal muscle development. Aberrant marker expression by RMS cells correlated significantly with patients ' survival.