Malignant rhabdoid tumor of soft tissues: a cytopathological and immunohistochemical study

We describe the cytopathological and immunohistochemical features of a primary malignant rhabdoid tumor (MRT) located in the left forehead region of an 8-mo-old female. The cardinal characteristics are hyaline cytoplasmic inclusions, rounded or bean-shaped nucleus, vesicular chromatin, central prominent nucleolus, and poorly defined cytoplasmic profile. Both the cytoplasm and the hyaline inclusion are vimentin and keratin positive, but negative with desmin, S-100 protein, neuron-specific enolase, (NSE) myoglobin, leukocyte common antigen (LCA), and alpha-1-antichymotrypsin. This immunohistochemical pattern, although not exclusive to MRT, is fairly typical of MRT, and when it is assessed in conjunction with cytopathological findings and clinical data permits a confident diagnosis of MRT. We emphasize the utility of immunohistochemical techniques in making the differential diagnosis of MRT against other childhood round-cell tumors.