Mixed epithelial and stromal tumor of the kidney lacks the genetic alterations of cellular congenital mesoblastic nephroma

Mixed epithelial and stromal tumor of the kidney is a recently recognized n eoplasm that occurs almost exclusively in perimenopausal women. Because it frequently contains areas of smooth muscle in which epithelial structures a re embedded, some have concluded that it is the adult form of congenital me soblastic nephroma. Others have concluded that the morphology and epidemiol ogy of mixed epithelial and stromal tumor indicate that it is unrelated to congenital mesoblastic nephroma. Although the genetic alterations of mixed epithelial and stromal tumor have not been previously elucidated, much is k nown about the genetic alterations of cellular congenital mesoblastic nephr oma. The present study was undertaken to determine if mixed epithelial and stromal tumors have any of the genetic alterations recognized as typical of cellular congenital mesoblastic nephroma. RNA extraction was performed on formalin-fixed, paraffin-embedded tissue from 7 mixed epithelial and stroma l rumors followed by reverse-transcription polymerase chain reaction to det ect the ETV6-NTRK3 gene fusion. Fluorescent in situ hybridization with cent romere-specific probes for chromosomes 8, 11, and 17 was performed to evalu ate polyploidy of these chromosomes in 11 cases of mixed epithelial and str omal tumor. None of the mixed epithelial and stromal tumors showed any of t hese genetic alterations. We conclude that mixed epithelial and stromal tum or of the kidney lacks the genetic alterations typical of cellular congenit al mesoblastic nephroma, is unrelated to it, and the appellation "adult mes oblastic nephroma" should not be used for these tumors. Copyright (C) 2001 by W.B. Saunders Company.