Heterogeneous Cell Growth in Human Brain Tumors; an Analysis of the BrdU-Labeling Index and the NOR Histogram

Abstract

Nucleolar organizer regions (NORs) are segments of DNA which encode ribosomal RNA (rRNA) and form loops within the nucleoli of cells [1]. Recently, many pathologists have begun to pay much attention to this region since the acidic proteins bound here can be visualized with the silver colloidal technique on histologic sections [2,3], and their increase in number seems to be related to the malignancy of tumors [1,4]. In order to study the significance of the number of silver-stained regions (AgNORs) in the evaluation of tumor malignancy, the AgNOR count per cell and the bromodeoxyuridine labeling index (BrdU LI) have been compared in human brain tumors [5,6]. These studies demonstrated a linear relationship between these two parameters in meningiomas [5] and in glial tumors [6]. On a cytological basis, however, evidence that indicates a direct connection between the increased AgNOR count and the cellular proliferative activity are not yet clear. Therefore, in the present study, we tried to re-evaluate the implications of AgNOR count in brain tumors, especially in relation to the growth activity of the cells. Special attention was paid to whether or not the AgNOR histogram may change in accordance to the regional heterogeneity of the BrdU LI, which is noted in human as well as in experimental brain tumors [7].