Full-thickness excision of tissue of a lesion in a lumen is performed through a natural orifice. Specifically, the tissue surrounding the lesion that is in a folded state is joined and severed using a linear stapler. The linear stapler includes a cutter and is inserted into the lumen. Joining and cutting is performed while organs outside of the lumen are pushed in a direction away from the lesion with the tip of the linear stapler. As a result of these steps being repeatedly performed along the periphery of the lesion, the lesion is excised.
