Nucleolar organiser region (NOR) distribution as a diagnostic marker in oral keratosis, dysplasia and squamous cell carcinoma

Nucleolar organiser regions (NORs) were quantified from a range of oral mucosal biopsies (n = 40) consisting of benign, reactive, dysplastic and carcinomatous lesions, using silver (Ag) staining, to see if AgNOR counts were helpful in distinguishing them. Mean counts were greater in carcinomas (8.37 +/- 6.11) compared to epithelial dysplasias (5.61 +/- 4.63) or benign keratoses (4.51 +/- 2.57). Although these differences were significant, counts in each diagnostic group overlapped so much that they were of no practical value in distinguishing between individual lesions. However, the higher counts found in many carcinomas were due to dispersion of AgNORs within the nucleoplasm, so that the AgNOR type is helpful in making such a distinction. Whether those dysplastic lesions with higher and more dispersed counts represent those at greater risk of malignant transformation awaits longitudinal study.