A surgical instrument assembly for use in snare cauterization operations comprises a tubular sheath member, a metallic cauterization loop, and a metal wire operatively connected to the loop, the wire passing longitudinally through the sheath. An electrical supply is operatively connectable to the wire for feeding an electrical current to the loop via the wire, while a manually actuatable shifter is operatively connected to the wire for longitudinally sliding the wire along the sheath in alternately opposite directions. A flexible web member is connected to the loop to form a capture pocket, the loop defining a mouth opening of the pocket. During use of the snare cauterization instrument, the loop is at least partially expanded from a collapsed configuration and passed over a polyp to be removed, so that the web member substantially surrounds the selected polyp. The loop is then closed to engage the polyp around a base region thereof and an electrical current is subsequently conducted through the loop to burn through the polyp at the base region thereof. Severance of the polyp occurs upon a closure of the cauterization loop by its being withdrawn or retracted into the tubular sheath member. The severed polyp is automatically captured by the web member.