An endoscopy discovered a "giant lateral spreading duodenal lesion" it is not malignant.. is it usual for these to become malignant ?

What's the biopsy?: More than likely, the endoscopist biopsied the lesion in question. The histology of this lesion, not included with your question, will likely address your concern. Please discuss the results with your doctor who may choose to perform additional biopsies or order a ct scan to best prognose the extent and future course of your lesion (e.g. Whether surgery is needed or spread is possible).