A rare but highly lethal childhood tumor found almost exclusively in infants. Histopathologically, it resembles RHABDOMYOSARCOMA but the tumor cells are not of myogenic origin. Although it arises primarily in the kidney, it may be found in other parts of the body. The rhabdoid cytomorphology is believed to be the expression of a very primitive malignant cell. (From Holland et al., Cancer Medicine, 3d ed, p2210).