Helpful parameter for malignant potential of gastrointestinal stromal tumors (GIST)

Although a series of histopathological criteria have been suggested, the prediction of the malignant potential of gastrointestinal stromal tumors (GIST) is still difficult. The older literature called all gastrointestinal stromal tumors smooth muscle tumors or mixed GIST with true smooth muscle tumors. Reports on GIST including homogeneous cases were rare.

We examined 73 cases of GIST, which were immunohistochemically positive for c-kit and/or CD34, and mainly focused on the correlation between mitotic count and the other clinicopathological features to establish any helpful and reproducible parameters to indicate the malignant potential and to be used practically and objectively in the routine histopathological diagnosis of GIST.

The results showed that there was a statistically significant difference in mitotic count between benign and malignant groups. Other proposed parameters, such as high cellularity, tumor size > or =5 cm, stomach and intestinal location, hemorrhage, necrosis, p53 expression and Ki-67 labeling index >10%, were frequently observed in tumors with mitotic figure. Three patients with one mitotic figure in 50HPF died from metastasis or recurrence of the tumors.

Ki-67 index and cellularity should be used as predictors for the malignant potential of GIST. When other morphological features appear benign, mitotic count might also be a helpful practical factor in the prediction of the malignant potential of GIST.