Plastic vs. metal stents for malignant biliary obstruction
Endoscopic stenting is the most common palliative treatment for biliary obstruction in people with unresectable pancreatic cancer. For decades, fixed-diameter plastic stents have been successfully used to relieve jaundice and improve overall quality of life in these patients.
But plastic stents occlude after about three months because their size — the diameter of the working channel of the endoscope — encourages bacterial biofilm growth and biliary sludge accumulation. Various modifications to address these problems, including large bore stents, have not been shown to increase patency, and plastic stent use in patients with longer life expectancies is likely to result in recurrent jaundice and increased interventions and hospital stays.
Self-expandable metal stents (SEMSs), which have post-expansion diameters ranging from 6 to 10 millimeters — three times that of plastic stents — were developed to overcome these limitations. Larger diameters increase patency duration to six months or more and reduce biofilm formation. But SEMSs have their own drawbacks. Todd H. Baron Sr., M.D., of Mayo Clinic in Minnesota, explains, "In the early days, we used bare metal stents, which integrate into the wall of the bile duct and are impossible to remove if they become blocked."
The solution was to cover the devices — first partially, leaving only the ends uncovered — and then fully, with silicone or PTFE. This prevents tissue embedding and stent-induced hyperplasia and prolongs patency by stopping tumor ingrowth. Limitations of covered SEMSs include cost, migration — occurring in about 10 percent of cases — and an increased risk of cholecystitis, which can occur when the stent prevents the gallbladder from draining.
Results of randomized controlled trials of covered and uncovered SEMSs have been mixed. In a 2001 study by Dr. Baron's group, covered stents appeared to have increased patency. But a recent Canadian meta-analysis published in Clinical Gastroenterology and Hepatology found no difference between the two stents in complications, hospital stays, recurrent biliary obstructions or patency at six and 12 months.
As expected, the study showed that covered SEMSs had a higher migration rate but a lower rate of tumor ingrowth, confirming that their chief advantage may be removability. Dr. Baron points out, "If a patient who appears to have pancreatic cancer is treated with an uncovered stent and then turns out to have another disease — say, autoimmune pancreatitis — you're left with a metal stent you can't remove. If there is any uncertainty in the diagnosis, it's preferable to use a covered stent. Our group and others have successfully used covered stents off-label for nonmalignant disease because they don't embed."
The choice of stent depends on patient prognosis and the relative costs of metal stents and repeat endoscopic retrograde cholangiopancreatographies. In general, plastic stents are reasonable for patients surviving less than three months and metal stents more cost-effective for patients expected to live longer. The problem is reimbursement.
Dr. Baron points out that not all insurers reimburse enough to cover the institutional cost of metal stents. Plastic stents, on the other hand, which require periodic replacement for prevention or treatment of blockage, are fully reimbursable.
"A private practitioner can justify bringing a patient back every three months and receive reimbursement," he says. "If an endoscopist places a metal stent, it often prevents the patient from requiring additional procedures, but the potentially incomplete reimbursement is not cost-effective from an institutional standpoint. That and reimbursement for additional procedures may be why plastic stents are still often used in longer-surviving patients."
Stents for neoadjuvant therapy
Studies indicate that metal stents are clearly superior to plastic for pancreatic cancer patients undergoing neoadjuvant therapy before surgical resection. Recent research has shown complication rates up to seven times higher when plastic stents are used preoperatively.
"No one knows whether it's better in these cases to use a covered or uncovered stent, but uncovered stents make sense because they are removed with the specimen," Dr. Baron says, adding, "The bottom line is that from a safety and cost perspective, it's better to use plastic stents in people with poor functional status and a predicted survival of less than three months and metal stents in patients who have a better prognosis or are undergoing preoperative therapy."
For more information
Almadi MA, et al. No benefit of covered vs uncovered self-expandable metal stents in patients with malignant distal biliary obstruction: A meta-analysis. Clinical Gastroenterology and Hepatology. 2013;11(1):27.
Baron TH. Expandable metal stents for the treatment of cancerous obstructions of the gastrointestinal tract. The New England Journal of Medicine. 2001;344:1681.