Primary Malignant Fibrous Histiocytoma Of Bone After Radiation

Two cases of primary malignant histiocytoma of bone after irradiation are reported. One tumour developed in the left ileal bone ten years after irradiation for cystadenocarcinoma of the left ovary. The other developed in the left mandible 26 years after irradiation for a »semi‐malignant« mixed tumour of the left parotid gland. Both tumours had a light microscopic picture of malignant fibrous histiocytoma as described in soft tissues. Fascicular, spindle‐cell areas resembling leiomyosarcoma were found in both tumours. Ultrastructurally the pelvic tumour was found to be composed of histiocytic and fibroblastic cells and some spindle‐shaped cells with abundance of myofilaments with dense body‐like structures, indistinguishable from spindle‐cells of leiomyomatous tumours. The light and electron microscopic observations suggest that a relationship exists between fibroblastic, histiocytic and leiomyomatous cell elements of bone and soft tissue tumours.