A method of treating a lesion of a tubular organ that communicates with a natural orifice of a subject is provided. In the method, a channel of the tubular organ is closed or substantially closed at a desired first position on a far side of the lesion. Then, the channel is closed or substantially closed at a second position near the orifice, i.e. on a near side of the lesion. Then, the tubular organ is linearized by charging a fluid into a closed space formed between the first and second positions by bringing the tubular organ into a closed or substantially closed state. Treatment tools are inserted into the linearized closed space to treat the lesion.
