A tissue resection system includes an endoscope including a stop ring extending about a distal portion thereof a resection head mounted over the distal portion of the endoscope distally of the stop ring, the resection head including a resection chamber within an outer wall thereof a first positioning mechanism abutting the stop ring to move the resection head relative to the endoscope between a first position in which a distal end of the resection head is proximal of a distal end of the endoscope and a second position in which the distal end of the resection head is distal of the distal end of the endoscope and a second positioning mechanism moving a first portion of the outer wall relative to a second portion of the outer wall to open and close the resection chamber.
