CLONAL ANALYSIS OF SACROCOCCYGEAL TERATOMAS

Congenital masses of the sacrococcygeal region commonly contain multip le tissues and have variously been subclassified as neoplasms or conge nital hamartomas based on clinicopathological and embryological observ ations. We have used a polymerase chain reaction-based assay for nonra ndom X chromosome inactivation to infer the clonality of three congeni tal sacrococcygeal tumors previously diagnosed as teratomas. One solid immature teratoma was monoclonal, and a predominantly cystic histolog ically mature mass was polyclonal. A third immature teratoma was nonin formative because of baseline asymmetry of polyclonal tissue X inactiv ation. We confirm that immature teratomas at this site appear to be mo noclonal neoplasms and suggest that at least some histologically matur e ''teratomas'' are more appropriately classified as hamartomas.