"The best [colorectal cancer screening] test is the one that gets done"

Last week was a busy one for cancer screening. I could choose to criticize the Centers for Disease Control and Prevention's premature guidelines to screen all baby boomers for hepatitis C (which can lead to cirrhosis and liver cancer) or the less-than-sound recommendations of several major cancer organizations to screen present or former heavy smokers between ages 55 and 74 for lung cancer with CT scans. (As I've pointed out before, there are at least 4 good reasons not to reflexively follow the latter advice.) But instead, I would like to explore the irony that another screening test that has conclusively been shown to result in more health benefits than harms is on the verge of becoming extinct in the U.S. That test is screening for colorectal cancer with flexible sigmoidoscopy.

Flexible sigmoidoscopy is an uncomplicated office procedure that requires no anesthesia and was once commonly taught to, and performed by, thousands of family doctors and general internists in adults over the age of 50. But over the past decade, gastroenterologists have done a magnificent job convincing primary care physicians and the American public that colonoscopy is the "gold standard" for colorectal cancer screening. As a result, a recent national survey found that while 55 percent of respondents reported receiving a screening colonoscopy within the past 10 years, only 1.3 percent of respondents reported being screened recently with flexible sigmoidoscopy.

That's too bad, because not only does screening colonoscopy cost a lot more money, it hasn't ever been shown to be more effective than screening sigmoidoscopy. In fact, screening colonoscopy has never even been tested in a randomized trial, and may never be. In contrast, yesterday the lead researchers of the National Cancer Institute's Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (which previously found that prostate and ovarian cancer screening don't save lives) reported that having a flexible sigmoidoscopy every 3 to 5 years reduced deaths from colorectal cancer by 26 percent, even though nearly half of the control group underwent screening at least once. That's a big deal, since colorectal cancer is the third-leading cause of cancer death among U.S. women, and the second-leading cause of cancer death in men under age 75.

In an accompanying editorial, Dr. John Inadomi urges clinicians to reconsider flexible sigmoidoscopy as a preferred cancer screening strategy for three reasons: 1) it's more evidence-based than screening colonoscopy; 2) patients are more likely to be screened if multiple options are available; 3) screening resources are limited, and efficiency matters. He concludes:

Where does this leave us with regard to screening flexible sigmoidoscopy? First, it should be acknowledged that flexible sigmoidoscopy reduces colorectal-cancer incidence and mortality for the portion of the colon that it is designed to examine. Next, high-quality evidence must show the superiority of colonoscopy over other screening tests before we dismiss the use of flexible sigmoidoscopy and fecal occult-blood testing, both of which have randomized, controlled trials supporting their benefit. Especially critical are data that confirm the ability of colonoscopy to reduce mortality from proximal cancers. Finally, patient preferences for screening tests should be identified and respected — in this case, the best test is the one that gets done.