SMN1 and gastrointestinal stromal tumor: However, CD117 (usually positive in GIST) and SMA (usually positive in leiomyoma) were positive in 6.4% (5/78) and 17.9% (14/78) of the patients, respectively, suggesting that a single IHC parameter could not differentiate GISs from GIST and leiomyoma, and a combination of several parameters is necessary.