Role of nucleolar organiser regions in differentiating malignant from benign tumours of the colon.

An argyrophilic technique (AgNOR) was applied to paraffin wax sections of 12 tubular adenomas, 17 villous adenomas with moderate and severe atypia, and 21 colonic adenocarcinomas. The range of the mean number of nucleolar organiser regions (NORS) per nucleus was 1.54-3.28 (99% CI 2.29-3.04) for tubular adenomas 3.07-4.36 (2.98-4.43), and 3.60-5.02 (3.74-4.69) for villous adenomas with moderate and severe atypia, respectively, and 5.53-9.33 (6.15-8.54) for highly differentiated adenocarcinomas. The number of AgNORs permitted differentiation among the three groups. The differences observed were significant. Malignant tumour cells were characterised by a large number of AgNORs which were small in size and showed a scattered distribution. Nuclei of tubular adenoma and villous adenoma with moderate atypia had only a small number of large sized AgNORs in a clustered distribution. It is suggested that this method distinguishes malignant epithelial cells from benign cells of colon, even those with severe atypia, and that it is a useful adjunct to diagnostic histopathology.