Evaluation of malignancy using Ki-67 labeling index for gastric stromal tumor

Assessment of malignant potential in gastrointestinal stromal tumors (GISTs) is still problematic. The maximum tumor diameter and the mitotic index are generally used as an index of malignancy of GISTs. The Ki-67 labeling index has recently been used as an index of cell growth, and the prognosis of GISTs was reported to be significantly poor when the value of this index was 10% or higher.

Clinicopathological and immunohistological factors were analyzed in 15 patients who underwent surgical resection of gastric stromal tumors at our department between April 1997 and July 2002. The patients were divided into "metastasis/recurrence" and "benign" groups. Also, the relationship of changes in the Ki-67 labeling index to the degree of malignancy in recurrent lesions was assessed in an 84-year-old woman who underwent five reoperations because of recurrences in the peritoneum.

Significant differences were noted between the metastasis/recurrence and benign groups in relation to the mean maximum tumor diameter (186.7 +/- 80.8 mm vs 41.3 +/- 22.9 mm), mitotic index (88.3 +/- 5.0/50 high-power fields [HPF] vs 3.0 +/- 2.9/50 HPF), and the Ki-67 labeling index (11.4 +/- 2.5% vs 0.01 +/- 0.51%). In the patient who had metastasis to the liver 3.5 years after initial operation and underwent five reoperations before death, the intervals until detection of recurrence tended to be shortened gradually. The Ki-67 labeling index varied with each operation, and tended to be higher at the time of reoperations than at the initial operation.

The maximum tumor diameter, mitotic index, and Ki-67 labeling index were useful as an index of malignancy for gastric stromal tumor. The efficacy of surgical resection alone may be insufficient in patients with disseminated metastasis to the peritoneum.