Malignant rhabdoid tumors: a clinicopathologic review and conceptual discussion.

The malignant rhabdoid tumor (MRT) has been a controversial lesion since its seminal description. There is no consensus as to whether it represents a distinctive clinicopathological entity or, alternatively, a phenotypic pattern that is potentially common to several disparate neoplasms. MRT of the kidney is a childhood tumor that is associated with uniformly aggressive behavior, but it shows a wide spectrum of histologic, immunophenotypic, and cytogenetic findings. Malignant extrarenal rhabdoid tumors (MERTs) have been observed in pure form over a broader range of patient ages and anatomic locations, but they show substantial morphological and biological homology with renal MRT. Lastly, "composite" extrarenal rhabdoid tumors (CERTs)--in which recognizable "parent" neoplasms are admixed with MERTs--also have been recognized in several topographic sites. In aggregate, these observations suggest that "rhabdoid tumors" are a heterogeneous group of lesions with dissimilar lineages of differentiation. Particularly in CERTs, it is likely that the rhabdoid phenotype represents a common end point of clonal evolution in tumors of clearly different origins. Despite these caveats, the authors do support retention of the diagnosis of "rhabdoid tumor," because the affiliated morphological pattern is uniformly attended by aggressive biological behavior despite potential dissimilarities at a subcellular level.