Stomach cancer. Endoscopic view of an ulcerated malignant (cancerous) gastrointestinal stromal tumour (GIST) of the stomach. GISTs are rare tumours that develop in mesenchymal tissue (muscle, connective tissues and bone). Symptoms include trouble swallowing (dysphagia), gastrointestinal haemorrhage or secondary tumours. Treatment options for soft tissue sarcomas such as this include surgery, radiation therapy, and chemotherapy.