Of the NF1 group, 24% had developed malignant tumours (16% carcinoma, 7% sarcoma, 1% melanoma) and 17% had developed benign tumours (7% GIST, 6% pheochromocytoma, 3% adenoma and 1% meningioma). The gene discussed is NF1; the disease is gastrointestinal stromal tumor.