Experimental rhabdomyosarcoma with regions like malignant fibrous histiocytoma (MFH)--a true double phenotypic pattern?

In murine sarcomas induced by 20-methylcholanthrene, histological features of malignant fibrous histiocytoma (MFH) as well as rhabdomyosarcoma were found in the same tumour both at light microscopy and at ultrastructural level. The areas showing rhabdomyomatous differentiation expressed vimentin, desmin, muscle-specific alpha-actinin, and sometimes myoglobin, but in the MFH areas only vimentin was expressed. A series of allografts in athymic mice, using tumour areas of both histological types, showed in every case a mixed pattern of tumour growth, whether the transplanted tissue was of MFH or rhabdomyosarcomatous type. This suggests that the MFH areas in the original experimental sarcomas were modulated disguised rhabdomyosarcomas. The significance of MFH-like areas in non-related soft tissue sarcomas is also discussed.