Sphincter preservation in rectal cancer.
Distal rectal cancer poses two challenges to the oncologist: local tumor control and sphincter preservation. The abdominoperineal resection (APR), long considered the standard treatment of tumors with a distal edge located up to 6 cm from the anal verge, provides local control in many patients but results in sphincter loss with a permanent colostomy. This is a critical limitation. Consequently, there has been significant interest in sphincter-conserving approaches, frequently combining chemoradiation with surgery. These approaches have evolved along two fronts. For patients with small rectal cancers confined to the rectal wall, local excision techniques with and without chemoradiation may offer comparable local control and survival rates as an APR and preserve sphincter function. For patients with larger and more invasive tumors of the distal rectum where local excision is inappropriate, preoperative chemoradiation promotes tumor regression and may facilitate a resection sparing the sphincter with a coloanal anastomosis. Preliminary results from single institution studies appear promising. In both these settings (favorable and more invasive rectal cancer), chemoradiation is employed to compensate for the limitations of the sphincter-preserving surgical technique. In local excision procedures, the excision margins are invariably small, and the mesorectum (lymphatics, soft tissue) surrounding the tumor is not excised. For patients undergoing resection with coloanal anastomosis, there are narrow radial and distal surgical margins. With these approaches of chemoradiation and sphincter-sparing surgery, satisfactory local control and survival with avoidance of colostomy are possible for many patients with distal rectal cancer.
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