A medical instrument includes a flexible sheath and an end effector. The sheath has a distal end. The end effector is attached to the sheath proximate the distal end and is insertable into a patient. The end effector includes opposing and retroflexed first and second jaws and includes at least one medical-treatment electrode supported by the second jaw. At least one of the first and second jaws is rotatable. In one implementation, the at-least-one medical-treatment electrode is operatively connectable to a medical radio-frequency (RF) generator. In one application, the end effector is insertable into the esophagus of a patient. In one employment, the first and second jaws are adapted to grasp a working end of a flexible tube of an endoscope.