Nucleolar organiser regions in normal, hyperplastic, and neoplastic endometria.

Nucleolar organiser regions (NORs) can be visualised by a silver stain that shows NOR-associated proteins as black intranuclear dots (AgNORs). NORs are loops of DNA that transcribe to ribosomal RNA, and the number of AgNORs is thought to reflect cellular proliferative activity. A study of AgNOR counts in normal, hyperplastic, and neoplastic endometria is reported. The highest AgNOR counts were found in normal proliferative endometrium and in well-differentiated endometrioid adenocarcinomas that were invading the myometrium. A mean AgNOR count of greater than 9 in curettage material from an atypical proliferative lesion of the endometrium is highly suggestive of an invasive neoplasm.