Cytokeratin subunits of inclusion bodies in rhabdoid cells: Immunohistochemical and clinicopathological study of malignant rhabdoid tumor and epithelioid sarcoma

Extrarenal malignant rhabdoid tumor (MRT), which is recognized as being his tologically similar to renal MRT, is characterized by the presence of "rhab doid cell" IRC) and a highly aggressive biological behavior. Recently it ha s been proposed that "proximal variant" of epithelioid sarcoma (ES), whose morphology is similar to that of MRT, actually has a more aggressive clinic al course than classical type ES. Detailed immunohistochemical analysis of c)cytokeratin (CI() subunits was performed in 3 cases of extrarenal MRT. 3 cases of renal MRT, and 11 cases of ES comprising 2 "proximal variants" and 9 classical types. Renal and extrarenal MRTs showed positive immunoreactiv ity for both CK8 and CK18. Classical type ESs were diffusely positive, nor only for CK8 and CK18, but also for other cytokeratin subunits including CK 4, 6, 10, 13, 16, 17. and "high-molecular-weight" CKs (CK1, 5, 10, and 14). On the other hand, proximal ES revealed limited immunohistochemical reacti vity for cytokeratins, compared with classical ES. In conclusion. the inclu sion bodies of RCs show immunoreactivity confined to CK8, CK18, and vimenti n, Furthermore, ES has additional CI( expressions, while proximal ES posses ses characteristics intermediate between those of classical ES and those of external MRT.