《Slide 209.》GIST of high malignant potential, Stomach
A. Brief Descriptions：
Most gastrointestinal mesenchymal neoplasm are GISTs.
The predominant location is stomach.
GISTs are immunohistochemically positive for CD117, which perhaps their single defining feature.
These tumors were designated as leiomyoma, cellular leiomyoma, or leiomyosarcoma mostly before.
B. Gross Findings：
Submucosal tumor mass with intact or ulcerated mucosa.
C. Micro Findings：
The majority of GISTs are spindle cells with variety of histological pattern.
Malignancy is based on mitotic counts and size.
< 5cm: usually benign.
Mitotic counts more than 5/50 HPF : low-grade malignant potential.
> 5 cm and mitotic counts less than 5/50 HPF: uncertain malignant potential.
> 10 cm : high malignant potential.
【 Fig. 209-1 (LP)】The tumor is composed of spindle cells in interlacing pattern.
【 Fig. 209-2 (LP)】Focal necrosis is noticed with tumor.
【 Fig. 209-3 (LP)】The tumor cells have pleomorphic nuclei and frequent mitotic figures (>5/50 HPF).
【 Fig. 209-4 (LP)】Immunohistochemical study shows cytoplasmic positive reaction with CD117 (brown color).