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

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Gastrointestinal stromal tumors: are they of cajal cell origin?

Recently some reports have suggested that gastrointestinal stromal tumors (GIST) might originate from the interstitial cells of Cajal or differentiate into them because they express c-kit and/or CD34 and indicated that the majority of previously diagnosed smooth muscle tumors (SMT) actually belong to GIST, but are not true SMT. We, therefore, detected c-kit, CD34, SMA, and S-100 in 106 Chinese cases of gastrointestinal tumors, which were histopathologically diagnosed as smooth muscle tumors originally, to demonstrate the immunophenotypes of these tumors. The results showed that 73 cases had immunoreaction with c-kit and/or CD34, of which 48 cases showed coexpression with either SMA or S-100 or with both. A correlation between the immunophenotypes and known histopathological parameters was also shown here based on follow-up data. We suggest that the concept of GIST should not be used as an umbrella to cover all gastrointestinal mesenchymal tumors, but be defined in a narrow term as differing from true smooth muscle tumors.