AgNOR staining in benign hyperplasia and carcinoma of the prostate.

We have modified existing techniques for silver staining of nucleolar organizer regions of intact interphase cells by hypotonic swelling and by formic acid treatment to reduce background staining. This allowed the microscopic identification and counting of individual AgNORs in the nucleoli. The method was used on nine adenomatous prostatic samples (including one of normal prostate tissue outside a localized tumor) and on seven prostatic adenocarcinomas. In general, the adenomatous samples displayed fewer AgNORs (mean 13 dots/cell) than did the carcinomas (mean 24 dots/cell). Although no cells with very high AgNOR counts were found in specimens from nonmalignant tumors, two of the adenomatous prostates did have AgNOR profiles that to a large extent overlapped with those of carcinomas. A highly differentiated carcinoma (of which only very small amounts were present in the sample) had low AgNOR counts. The three moderately differentiated carcinomas had more silver-positive material than the nonmalignant prostates but less than the three poorly differentiated carcinomas. The latter tumors also had a substantial proportion of cells with greater than 60 AgNOR counts, something that was never seen in carcinomas with higher differentiation. The data indicate that analysis of silver staining-positive material in intact interphase cells may help distinguish between benign and malignant prostatic tumors and between highly malignant and low malignant carcinomas.