From OncoLog, December 2007, Vol. 52, No. 12

A Step Forward for Stents

by Dianne Witter

Jeffrey H. Lee, M.D., guides the endoscope and its attached accessories carefully into the patient’s esophagus, keeping track of the scope’s whereabouts on monitors that show real-time video images. Introduced through the endoscope is a stent made of thin, flexible metal mesh.

The stent, collapsed for the journey, is roughly the diameter of a straw. Dr. Lee, an associate professor in M. D. Anderson’s Department of Gastroenterology, Hepatology, and Nutrition, guides the device through the duodenum to the opening of the bile duct, which is his destination.

With the help of images from computed tomography, endoscopic ultrasonography, and fluoroscopy, he carefully threads a guide wire into the obstructed passageway and advances the stent into the bile duct. Once the stent is placed, it expands to open the duct and allow bile to flow again. On the monitor, a gush of dark bile from the end of the stent signals success.

An obstructed bile duct is a frequent complication of pancreatic cancer that can cause fever and potentially life-threatening infection. As tumors in the head of the pancreas grow, they tend to crowd the bile duct, narrowing the passageway until the flow of bile is slowed or even stopped. Plastic stents have been used for years to relieve such obstructions, but these stents have significant drawbacks, such as the tendency to clog within 3 months of placement. Once a stent is occluded, complications such as cholangitis and cholestasis are likely to develop, and a new stent must be placed.

Fortunately, stents—and the materials that go into them—are improving quickly. Their use has become more important as therapy changes.

“More and more, physicians are administering preoperative chemoradiation in locally advanced pancreatic cancer, which increases the time to surgery and, therefore, increases the possibility of a biliary obstruction,” said Dr. Lee. “That has elevated the urgency of the need for stents that will stay open throughout preoperative treatment.”

The current state-of-the-art material for stents is a nickel-titanium alloy. A wire-mesh stent made of this alloy is pliable, conforms to the shape of the structure it is in, can be compressed for transport during placement, and is very unlikely to migrate once in place.

“In a 2005 study, we found that the metal stents didn’t get occluded as quickly as plastic stents and were associated with a lower incidence of cholangitis. Also, there was a reduced need for repeat endoscopic retrograde cholangiopancreatography (ERCP) with metal stents, and there were no more surgical complications than with plastic stents,” said Dr. Lee. “We also discovered that the metal stents, when appropriately placed, didn’t interfere with subsequent tumor resection.

“Based on these findings, at M. D. Anderson we changed from plastic to metal stents to treat biliary obstruction resulting from pancreatic cancer, and now others in the medical community are following suit.”

There are more advances on the horizon. M. D. Anderson researchers led by William Ross, M.D., associate professor in the Department of Gastroenterology, Hepatology, and Nutrition, are taking part in a multi-institution, phase III trial of a new metal stent that is covered with silicone to prevent tumor growth into the stent. Covered metal stents are expected to reduce the need for additional ERCP procedures and to lengthen the patency period. Concerns about covered metal stents, as opposed to metal mesh-weave stents, include the possibilities of stent migration and obstruction of the cystic duct.

Also in the pipeline are bioabsorbable stents designed to be taken up by the body within 1 to 3 months after placement. These have shown significant promise in animal studies and will likely move to human trials soon, especially for benign causes of biliary obstruction.

For more information, contact Dr. Lee at 713-794-5073.

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