DSRCT should be considered in the differential diagnosis of renal tumors composed of small round cells. Undifferentiated morphology and lack of desmoplasia contribute to the difficulty in its recognition. Ancillary studies such as immunohistochemistry may suggest the diagnosis, but cytogenetic and molecular genetic studies are required for confirmation.

Neoadjuvant chemotherapy followed by resection has become the mainstay in the treatment of hepatoblastoma (HB). The changes after chemotherapy typically result in tumor necrosis and a fibrohistiocytic response. We have observed that treated HBs undergo additional morphologic changes that have not been described. Herein, we report a 15-year retrospective study of HBs in 22 children who received neoadjuvant chemotherapy according to the Children's Oncology Group protocols. The medical records, diagnostic imaging, and histopathology were reviewed. Besides treated HBs having characteristic necrosis and fibrohistiocytic response, two-thirds had areas of cytoarchitectural differentiation ("maturation") mimicking non-neoplastic liver, and a quarter had alterations mimicking hepatocellular carcinoma. Nuclear expression of beta-catenin and keratin profiles were useful in distinguishing residual tumor with "maturation" from non-neoplastic liver and therefore in the assessment of surgical margins. Statistical analysis revealed that larger pretreatment and posttreatment imaged tumor size, larger tumor size at pathologic examination, and vascular invasion were significant univariate predictors of metastatic disease, whereas pretreatment imaged tumor size and vascular invasion were also significant independent predictors (multivariate logistic regression analysis). Multifocality, greater posttreatment necrosis and hepatocellular carcinoma-like morphology were more often associated with metastatic disease, but did not reach statistical significance.