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Washington University Experience | NEOPLASMS (EMBRYONAL) | ATRT - Atypical Teratoid Rhabdoid Tumor | 16E3 ATRT. spinal & tectal (Case 16) INI1 5.jpg
INI1 shows loss of nuclear staining in the tumor but not in the endothelium or other non-neoplastic cells. ---- Ancillary data (not shown):Epithelial membrane antigen stains a small subset of tumor cells. Desmin shows no significant staining but smooth muscle actin stains scattered tumor cells. CD45 is negative. FISH to assess loss of 22q, the chromosomal region that includes the SMARCB1 gene encoding INI1, is negative. ---- Comment: In the setting of a small blue round cell neoplasm in a young child, loss of INI1 expression is diagnostic of atypical teratoid rhabdoid tumor (ATRT). Inactivation of the SMARCB1 gene, whose protein product is INI1, is the signature genetic alteration in this aggressive childhood malignancy. We are aware of an additional tumor in this child described as a "tectal glioma" which has not been biopsied. We think it most likely, but as yet unproven, that this spinal mass may represent a "drop met" from the primary tumor.
