The spindle type GISTs must be distinguished from many kinds of tumors, such as fibromatosis (can be weakly CD117 positive), leiomyoma (beware of intermixed CD117-positive cells), leiomyosarcoma, schwannoma, malignant peripheral nerve sheath tumor, inflammatory myofibroblastic tumor, inflammatory fibroid polyp (may have PDGFR-α mutations), solitary fibrous tumor, synovial sarcoma, dedifferentiated liposarcoma, endometrial stromal sarcoma, sarcomatoid carcinoma.[1]. The gene discussed is KIT; the disease is leiomyosarcoma.