Chromosome aberrations in mesoblastic nephroma.

Mesoblastic nephroma (MN) is the most common renal tumor diagnosed in infancy. Histologically, MNs are designated as classic, cellular, or mixed type based upon variations in cellularity. Recent karyotypic reports have suggested that extra copies of chromosome 11 are a nonrandom occurrence in MNs. We analyzed nuclear suspensions prepared from a group of 17 formalin-fixed, paraffin-embedded tumors to determine the possible role of chromosome 11 copy number in the genesis of MN. Extra copies of D11Z1 (a probe for the centromeric region of chromosome 11) were detected in seven out of 10 MNs with cellular or mixed histology, whereas each of six classic histology MNs were disomic for D11Z1 (P < 0.05). Additional fluorescence in situ hybridization studies utilizing the probes for the alpha satellite, centromeric regions of chromosomes 7, 8, 9, 12, 17, and 20 were then carried out on all cases with cellular or mixed histology. Five out of 10 cellular or mixed MNs had extra copies of D8Z1, and four out of 10 had extra copies of D17Z1, suggesting that gains of chromosomes 8 and 17 may be additional nonrandom cytogenetic events associated with the evolution of MNs. DNA aneuploidy, as determined by image analysis, was detected in three tumors: all had greater than four chromosomal aberrations documented by fluorescence in situ hybridization.