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Primary hepatic malignant tumor with rhabdoid features. A histological, immunocytochemical, and electron microscopic study of four cases and a review of the literature.

Malignant tumors of the liver with rhabdoid features (MTR) are uncommon: Only 14 previous cases are reported in the literature. These tumors are characterised morphologically by sheets of large polygonal cells with abundant eosinophilic cytoplasm containing a periodic acid Schiff's-positive hyaline globular inclusion and vesicular nuclei with a central prominent nucleolus. Immunohistochemically, the inclusions at least show positivity for vimentin and epithelial markers and sometimes for other antigens. Ultrastructurally, the inclusions are composed of whorled intermediate filaments. Despite the superficial resemblance to cells of muscle origin implied in the term rhabdoid, there is no immunohistochemical or ultrastructural evidence to support such a derivation. We describe four additional children with tumors of this type, in three of whom tumor cells showed focal membrane positivity for MIC-2 on immunostaining. Its expression in an hepatic MTR may indicate neuroepithelial differentiation. Hepatic MTR should be considered in the differential diagnosis of an undifferentiated primary liver tumor in an infant in whom the alpha-fetoprotein concentration is normal or only slightly elevated for age.