Malignant thymic tumor in an infant (malignant histiocytoma).

A 2-month-old infant was diagnosed as having an invasive thymic tumor. Histologically and ultrastructurally, the tumor was composed of primitive mesenchymal cells, most likely malignant histiocytes. The child died at the age of 5 1/2 months with metastases to the bone and and liver. Review of the literature on thymic tumors and fibrous histiocytomas or malignant histiocytoma shows no similar case.