Malignant rhabdoid tumor of the prostatic region. Immunohistological and ultrastructural evidence for epithelial origin.

We describe a malignant rhabdoid tumour of the prostatic region in a 14-year old boy. The tumour showed positive immunoreactivity for epidermal prekeratin, monoclonal cytokeratin, epithelial membrane antigen, carcinoembryonic antigen and monoclonal vimentin but was negative for myoglobin, alfa-fetoprotein and lysozyme. Electron microscopy revealed pleomorphic cells with collections of paranuclear intermediate filaments, sheaves of tonofilaments and abundant microvilli in some tumour cells. Epithelial derivation was also suggested by occasional intracytoplasmic lumina and rare cell junctions.