Neoplasm of the stomach Gastric leiomyosarcoma 2017-05-21T13:42:26Z A malignant neoplasm of the stomach that grows submucosally in the gastric wall. Necrosis and hemorrhage may be visible radiologically. Histologically, spindle cells with abnormal mitotic activity may be visible. Gastric leiomyosarcomas are often clinically silent until they reach a large size, bleed or rupture. Thus, the diagnosis is rarely made preoperatively. Since in many cases the mucosa is normal, a definitive diagnosis for resectable tumor is often made after surgery. Seeding of tumor deposits into the serosa or omentum is almost invariably a sign of malignancy.