U.S. Preventive Services Task Force Recommends Against General Screening for Pancreatic Cancer
的risk of false positives and invasive procedures due to screening is greater than the potential benefit, experts say.
Adults who have no symptoms do not benefit from screening forpancreatic cancer, and such screening should not be recommended, according toa paper published August 6 in theJournal of the American Medical Associationby the U.S. Preventive Services Task Force (USPSTF)。的USPSTFis an independent panel of experts who review evidence and make recommendations regarding preventive services used in primary care, such as cancer screenings and vaccinations.
的task force conclusions are not surprising. To date, there are no good, reliable, low-risk ways to screen for cancerous tumors in thepancreas。But the report is fodder for growing discussions on how to best diagnose and treat one of the most lethal forms of cancer. Pancreatic cancerkills about 46,000 Americans a year, according to the American Cancer Society,andmay soon surpass colorectal cancer as the second-leading cause of cancer deathin the United States, according to some estimates.
的disease is often detected at a late stage, progresses quickly, and is challenging to treat, saysChien-Wen Tseng, MD, MPH, a member of the USPSTF and a professor and associate research director in the department of family medicine and community health at the University of Hawaii John A. Burns School of Medicine in Honolulu.
的five-yearsurvival ratefor allstages of pancreatic cancercombined is only 9 percent, according to the American Cancer Society. “Even when we find it at early stages, it often doesn’t result in a cure,” says Dr. Tseng. “It’s a tough cancer. But it’s a rare cancer.”
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Evaluating the Evidence for Pancreatic Cancer Screening
To review the value of screening asymptomatic people for the disease, the USPSTF looked at 13 studies. Most of the research was done on individuals who are known to be at high risk for pancreatic cancer, such as those with a family history or who know they carried gene mutations, such as aBRCA gene, that elevate risk.
的task force issued a "D" recommendation, meaning experts found no evidence that screening can reduce death rates in asymptomatic people and that there is potential harm from screening. In 2004, the USPSTF alsoissued a "D" recommendationfor pancreaticcancer screeningof asymptomatic people.
"When we talk about screening, we want a test that is going to be extremely accurate at finding it in the very few people who have it and not finding it in the many people who don’t have it,” Tseng says. “Aside from just finding pancreatic cancer, we need to find it early enough so we can cure or treat it.”
的potential harm from screening asymptomatic people is a key part of the "D" recommendation, says Tseng. Imaging can sometimes find noncancerous lesions in the pancreas. These lesions may or may not become cancerous, while surgery to remove them can be risky.
"Up to 60 percent of patients who undergo surgical resection for a precursor lesion are found to have a lesion with a low risk of progression," wroteAnne Marie Lennon, MD, PhD,the clinical director of gastroenterology at Johns Hopkins University in Baltimore, in aneditorialaccompanying the recommendation paper.
Most Screening Options Have Limitations
的problems associated with screening asymptomatic adults are many, experts say. Imaging techinques, usingultrasound,MRI, or CT, are considered unhelpful in distinguishing harmless, noncancerous lesions from cancerous tumors. What’s more, the position of the pancreas, tucked behind the stomach, makes imaging particularly difficult.
"If you can see a lesion in the pancreas on aCT scan, which is the best method we have now, it's already a concern that it may be too late," saysKeith D. Lillemoe, MD, the chief of surgery at Massachusetts General Hospital in Boston, who was not involved in the USPSTF recommendation. "Right now, I don't see any imaging that helps us detect these lesions in a widespread fashion, such as with mammographic screening" for breast cancer detection.
Blood teststo look for DNA shed by the tumor into the bloodstream, called circulating DNA tests or liquidbiopsies, are in development, he adds. But none are ready for use in the clinic. "These are not tests readily available to the general public. Most are still done in the research perspective."
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For People at High Risk: A Question Mark
的"D" recommendation was only for asymptomatic people, not people who have an increased risk of developing pancreatic cancer. Whether people who are at higher risk for pancreatic cancer should be screened is unclear, though studies are underway to determine the answer.
People with a strong family history of the disease are considered at higher risk for pancreatic cancer, as are people with particular gene mutations or inherited genetic syndromes, including the BRCA 2 gene mutation, thePALB2基因突变, atypical multiple molemelanoma(FAMMM) syndrome, familialpancreatitis(usually caused by the PRSS1 gene mutation), Lynch syndrome (caused by mutations in the STK11 gene) and Peutz–Jeghers syndrome (caused by theSTK11 gene mutation).
Other factors may alsoincrease the riskof the disease, according to the American Cancer Society, such as being overweight; some workplace exposures, such as working around dry-cleaning chemicals; African American ethnicity; having diabetes orchronic pancreatitis; a diet high inprocessed foods; and heavy alcohol intake.
Anyone known to be at higher risk for the disease should talk to their doctor about disease prevention, says Tseng.
Gradual Improvement in Strategies for a Tough to Treat Cancer
Some experts express optimism about future improvements in the prevention, detection, andtreatment of pancreatic cancer。Researchers are particularly interested in studying the role of precancerous lesions that are sometimes found in the pancreas, to better characterize which ones pose a true risk of turning into cancer.
的se lesions are sometimes found by accident in people who are undergoing imaging for other reasons, says Dr. Lillemoe, who cowrotea second editorialaccompanying the USPSTF report. But more research is needed to understand which precancerous lesions need to be removed.
"These asymptomatic lesions can be found in 3 to 4 percent of all abdominal imaging done in this country," he says. "How do you determine which of these lesions to go chasing after? Surgery in the pancreas is a high-risk procedure. We don't want to hurt patients by removing a lesion that has no risk."
For people diagnosed with the disease, surgery to remove the cancer, while challenging, is safer than it used to be, Lillemoe says. Moreover, some patients can be treated with chemotherapy and radiation before surgery to improve their chances for longer survival.
Two decades ago, Lillemoe says, "For all comers with pancreatic cancer, the five-year survival rate was 3 percent. Now that number has more than doubled. We are now finding precursor lesions and have better surgical and better chemotherapy outcomes. So we have made progress."
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