The best test is the one that gets done

About one-third of Americans ages 50 to 75 have never been screened for colorectal cancer. Some are deterred by a lack of insurance or have limited access to care. Others fear colonoscopy — the most heavily promoted screening method. But physicians also bear some responsibility for the screening gap. Confronted with a growing number of options and competing guidelines, they may be reluctant to screen at all, according to gastroenterologist Michael F. Picco, M.D., of Mayo Clinic in Florida.

"There are several recommendations with regard to screening, and the guidelines are all over the map. But that's no reason not to enroll patients in some kind of screening program," he says.

Mixed messages

The problem isn't only an abundance of new tests. It's also that older methods are being phased out or undergoing increased scrutiny. Colonoscopy, in particular, has come under fire for its widely varying adenoma detection rates, expense, risks and low patient satisfaction. "We think colonoscopy is better, but that's a matter of increasing controversy," Dr. Picco says.

He still believes the best strategy is to visualize the colon — either with colonoscopy or CT colonography, which has largely replaced double-contrast barium enema. "CT may not be as sensitive for smaller polyps, but it is noninvasive, has no perforation or bleeding risk, and requires no sedation. Of course, if CT finds a polyp, colonoscopy would be needed to remove it."

But some experts, including the U.S. Preventive Services Task Force (USPSTF), don't endorse CT colonography as an alternative to colonoscopy. Instead, the USPSTF recommends high-sensitivity fecal occult blood testing (FOBT) or sigmoidoscopy with FOBT. Cost is an issue, too. Medicare bears the full cost of colonoscopy but after years of debate still does not cover CT.

Patients tend to prefer stool tests because they're simple and noninvasive, but the tests can lead to false positives and false negatives. Fecal immunochemical testing (FIT) — a newer, most sensitive test — may eventually replace high-sensitivity FOBT, but current guidelines consider both tests acceptable options. And just where the new stool DNA test will fit in the screening regimen remains to be seen.

"All the options can get mind-boggling, but the fact that there are many options is no reason not to do it," Dr. Picco says.

He recommends that physicians discuss the various screening methods with patients without endorsing a particular strategy and then decide on an approach based on patient preference and availability of modalities.

"All tests have drawbacks; no one method is superior," he says. "You have to enroll patients in the screening method that works best for them."

Aging out of screening

Almost everyone agrees that screening should begin at age 50 for average-risk patients, and, some suggest, at age 45 for African-Americans. But when screening should stop is more problematic. The USPSTF set the upper age limit as 75 after studies determined the benefits of screening people ages 76 to 85 were small compared with the risks. The American Cancer Society and American College of Gastroenterology, among others, don't specify an upper age limit.

Although guidelines vary, Dr. Picco points out that a general rule of thumb is not to screen after age 80 or when life expectancy is less than 10 years.

"At 80, most folks' life expectancy is usually not 10 years," he says, "so it's reasonable to stop in that case. In general, the guidelines should be followed relative to timing. When people shorten the interval against the guidelines, it's not a good use of resources."

But younger patients should be screened, he says. "Physicians need to get on board with that."