An endoscopic electrosurgical instrument is presented for encapsulating and resecting biologic tissue, such as a polyp, from an anatomical structure, such as a lumen. The instrument includes an encapsulation assembly which includes a snare coupled to an electrically non-conductive, shrinkable pouch in a drawstring-like configuration. The encapsulation assembly may be folded within the elongated cylindrical housing of the endoscopic instrument, positioned within the patient at the surgical site, and deployed for use. Once positioned over the polyp, the snare is tightened around the peduncle thereof, and the pouch is activated, thereby shrinking and encapsulating the polyp. The polyp may then be resected using conventional or electrosurgical techniques. The disclosed instrument may include surgical tools and / or electrosurgical electrodes for performing surgical procedures. The disclosed system may reduce the occurrence of undesirable arcing and may aid retrieval of resected tissue.