The disclosed technology is directed to a method of operating a treatment tool for excising a lesioned portion of a body tissue. The method comprises applying a treatment tool to the lesioned portion. The treatment tool includes an elongated sheath having a snare wire disposed therein. The snare wire is configured to be movable forward or backward along a longitudinal direction. Next, forming the snare wire into a loop and tilting the loop in a plane transverse to the longitudinal axis of the elongated sheath with a force tending to push a snare wire portion out of a distal-end opening of the elongated sheath. And finally, placing the loop around the lesioned portion of the body tissue to excise the lesioned portion in a state in which the snare wire positioned transverse to the lesioned portion.
