Smooth muscle tumors of the gastrointestinal tract. Expression of ras P21 oncogene product and the association with clinicopathology.

Quantitative analysis of ras oncogene product P21 was performed on paraffin blocks from 55 smooth muscle tumors of the gastrointestinal tract by immunofluorescence and flow cytometry. No positive evidence for P21 was found in 5 cases of normal smooth muscle tissues. Eight of 14 leiomyomas were P21 positive (57%) but all of them were lower expressed with fluorescence index (FI) < 1.25, whereas a total of 29 leiomyosarcomas and 12 potential malignant smooth muscle tumors were found to be P21 positive (100%), and the majority were overexpressed with FI > 1.25 (P < 0.005). ras P21 was overexpressed significantly in the tumors with mitotic counts of more than 1/10 high power field (P < 0.005). It was also overexpressed significantly as soon as the mild cytologic atypia of the tumor was found (P < 0.005). Five-year survival rate was significantly higher in the patients with lower-expression of ras P21 than those with overexpression (P < 0.005). It was suggested that the expression of ras oncogene product P21 could be used as an objective parameter in distinguishing malignants from benigns and predicting the prognosis of the patients with smooth muscle tumors of the gastrointestinal tract.