Argyrophilic nucleolar organizer regions in Wilms' tumors and related lesions: a histologic and chromosomal correlation.

The argyrophilic nucleolar organizer regions (AgNORs) have been extensively investigated in different neoplasms, and their increased number has been frequently linked to aggressive tumor behavior. To evaluate this association, 22 specimens from 21 patients with Wilms' tumors and related lesions were stained by the AgNOR silver-staining technique in formalin-fixed, paraffin-embedded tissue. The aim of the study was to assess the significance of AgNOR count independently or in relation to histology in predicting the behavior of these neoplasms. Eleven nonneoplastic pediatric kidneys were used as controls. The controls had a range of 1.55 to 2.26 AgNOR/nucleus with a mean +/- SD of 1.91 +/- 0.22. The tumors showed a range of 1.25 to 2.86 AgNOR/nucleus with a mean +/- SD of 2.10 +/- 0.38 with obvious overlap between tumors and controls. The two unfavorable histology Wilms' tumors and the malignant rhabdoid tumor showed no increase in the number of AgNOR (1.66, 2.04, and 2.05, respectively). We further quantitated the nucleolar organizer regions (NOR) in metaphase spreads of three of the neoplasms, compared those with the patients' peripheral blood, and showed no difference in NOR numbers except for an occasional decrease in G-group NORs in the tumor cells. Tumors that had metaphase NOR counts of 6 to 9/nucleus had a mean interphase AgNOR count of less than 2.5. These results suggest that quantitative analysis of AgNORs in Wilms' tumors and related lesions is not a reliable predictor of aggressive tumor behavior. The discrepancy between metaphase and interphase NOR counts indicates that AgNOR counts are merely the reflection of the spatial arrangement of NOR-bearing chromosomes.