Relationship between interphase AgNOR distribution and nucleolar size in cancer cells

We have studied the relationship between interphase nucleolar organizer region (NOR) distribution and nucleolar size in cancer cells at light-microscopical level. Thirteen cases of formalin-fixed bladder cancer and fifteen cases of methacarn-fixed tumours of different origin were used. Nucleoli of the former cases were stained by Phloxine B and of the latter by Toluidine Blue. Selective visualization of interphase NORs was obtained by carrying out the one-step silver staining reaction for AgNOR proteins (Ploton et al., 1986). The area occupied by Phloxine B- or Toluidine Blue-stained nucleoli and interphase silver-stained NORs was measured by means of an automated image analyser. Both in bladder cancers and in the other tumour lesions nucleolar and interphase AgNOR areas were linearly related (r = 0.95 and r = 0.96, respectively, P < 0.001). The close relationship between the area of nucleoli and that of silver-stained nucleolar structures was maintained even if the silver-staining procedure was prolonged beyond the optimal time length for selective interphase NOR staining. In the latter case, however, single interphase AgNORs were no longer visible within the nucleolar body which was, in fact, homogeneously stained. These data indicate that evaluation of the interphase AgNOR area has the same relevance, in tumour pathology, as whole nucleolar size measurement.