[Quantification of nucleolar organizers (NORs) in renal carcinomas. Comparison with the nuclear grade]

Twenty three renal tumours: 6 clear cell carcinomas, 3 granular cell carcinomas, 8 mixed cell carcinomas, 3 tubulopapillary tumours, 2 spindle cell carcinomas and 1 oncocytoma, were retrospectively submitted to a staining technique which reveals argyrophilic proteins related to Nucleolar Organizer Regions (NORs). The semiautomated quantification of the number and mean surface area of the argyrophilic granules was performed by means of a quantimeter. The results were compared to the nuclear grade, which constitutes the reference histological prognostic factor. A very good correlation was observed between NORs and nuclear grade. The mean number of argyrophilic granules per nucleus (n) and more particularly their surface area (s) were very significantly increased in high-grade carcinomas (n = 1.96), s = 3.72) in comparison with low-grade carcinomas (n = 1.50, s = 1.35). Quantification of NORs therefore allowed objective differentiation between a low nuclear grade and a high nuclear grade. The quantification method used emphasised the value of not only measuring the number but also the surface area of the argyrophilic granules.