A study of histopathological assessment criteria for assessing malignancy of gastrointestinal stromal tumor, from a clinical standpoint.

BACKGROUND

As no established histopathological criteria exist for assessing the malignant potential of gastrointestinal stromal tumor (GIST), recurrence or metastasis is occasionally observed in lesions diagnosed histopathologically as benign. The present study aimed to clarify the histopathological criteria for assessing the malignancy of GIST, from a clinical standpoint.

METHODS

The subjects were 22 patients with GIST expressing CD117 (c-kit) and/or CD34, who were followed up for more than 2 years. Clinically, GIST malignancy was diagnosed if any of the following criteria were met: peripheral invasive growth, lymph node metastasis, metastasis to another organ, peritoneal dissemination, recurrence, or death. GIST was also categorized as either benign or malignant by a new histological malignancy classification system, based on the determination of significant factors indicating malignancy in the clinical classification system above.

RESULTS

Significant factors for malignancy identified in the clinical malignancy classification were: tumor hemorrhage/necrosis (present vs absent; P = 0.0053), tumor size (<5 cm vs > or =5 cm; P = 0.0022), and Ki-67 labeling index (<3% vs > or =3%; P = 0.0002). A new histological malignancy classification, based on a combination of these three factors, was developed. A significant correlation existed between the clinical system and the new histological malignancy classification system (P = 0.0008). The recurrence-free survival rate was 100% in the histologically benign cases and 37.5% in the histologically malignant cases (P = 0.0012).

CONCLUSIONS

The new histological malignancy classification for GIST was demonstrated to be useful from a clinical standpoint.