Nucleolar organizer regions in myogenic stromal tumours of the stomach.

Silver staining of nucleolar organizer regions (AgNOR) was studied in 26 primary benign and malignant gastric stromal tumours of myogenic origin. The absolute number of AgNOR per nucleus and the size of AgNOR were compared with histomorphologic features of the tumours. The total number of AgNOR per nucleus in epithelioid and spindle cell leiomyosarcomas significantly (p less than 0.001) exceeded that in leiomyomas, cellular leiomyomas and epithelioid leiomyoblastomas. The mean number or the size of AgNOR did not correlate with the number of mitoses or the tumour size. In addition, large and bizarre AgNOR were seen predominantly in histologically malignant tumours. Only one exceptional epithelioid leiomyoblastoma recurred despite a lack of conventional characteristics of malignancy and a low AgNOR count. Therefore, quantitative determination of the number of AgNOR is a new independent variable in myogenic gastric tumours. It provides additional information for the histopathological evaluation of this heterogenous group of mesenchymal tumours.