Proof at Last? Colonoscopy and Cancer Prevention Do you really need that colonoscopy? It's a question that seems simple at first. After all, as more Americans routinely undergo the oft-dreaded colonoscopy with each passing year, cases of colorectal cancer have continued to drop. Yet data from large, conclusive studies that prove this test, currently the primary weapon in a doctor's arsenal to catch colon cancer early, actually saves lives has so far been lacking. Some doctors believe that new research, released Wednesday by the New England Journal of Medicine, takes a big step in this direction. In the study, researchers led by Ann G. Zauber of Memorial Sloan-Kettering Cancer Center in New York suggest that removing non-cancerous growths known as polyps could have a big impact on death from colorectal cancer. Doctors routinely remove these benign polyps during a colonoscopy. The new study indicates that people who have polyps removed slash their risk of death from colorectal cancer by more than 50 percent over the next decade and a half compared to the general population. "This study confirms the suspected benefit of colonoscopy as it relates to reducing mortality from colorectal cancer," says Dr. Fritz Francois of NYU medical center, who was not involved with the study. He added that while certain questions still remain surrounding the overall body of research on colonoscopy, "the important message is clear: colonoscopy saves lives." This message featured heavily in the wave of coverage from many major media outlets, including the New York Times and the Associated Press, that followed the release of the study. In one article, an expert suggests that the study "puts [the] argument to rest" over whether removing polyps saves lives. Another reads, "For the first time, a major study offers clear evidence" that colonoscopy keeps people from dying of colon cancer. But is this really what the study showed? Dr. Rita Redberg of the University of San Francisco, editor of the journal Archives of Internal Medicine, was less impressed by the new study. She said a major shortcoming of the study was that it did not factor in the so-called "healthy user effect." In other words, she said, those people in the study who received colonoscopies and had polyps removed may very well be more healthy than the average person in the general population - perhaps doing things like eating a healthier diet, exercising or taking medications regularly. These aspects of their lifestyle may lower their chances of developing colon cancer even before colonoscopy is considered. The healthy-user effect has confounded medical professionals before. Redberg said the healthy-user effect is "the same reason we thought hormone replacement therapy [HRT] was protective against heart disease for women for many years, until a randomized trial was done." In the case of HRT, when such a trial was performed, researchers actually found a slight increase in heart disease and strokes among women taking the measure that was supposed to have improved their health. Other doctors contacted by ABC News agreed that it is difficult to make any conclusions from the study at hand. That said, government health agencies have made prevention of colorectal cancer a top priority and, as a result, have strived to encourage more Americans to have screening colonoscopies. Current guidelines recommend that every American age 50 to 75 undergo screening colonoscopy - though CDC data suggest 22 million Americans who should be getting screened, aren't. The stakes for preventing colorectal cancer are high. In the U.S., among cancers that affect both men and women, colorectal cancer is the third most common and the second leading cause of cancer death, according to the CDC. And the idea that finding and removing precancerous polyps before they turn into cancer seems a logical way to try and solve the problem. So will doctors ever know conclusively whether or not colonoscopy and the removal of benign polyps save lives? Most experts contacted by ABC News believe so. "If your doctor finds a polyp on colonoscopy, that's a tissue we know may turn into cancer," said Dr. Eric Esrailian, a gastroenterologist at UCLA. It can be removed during the procedure and the cancer never develops... We can basically prevent cancer. Until this can be proven more conclusively, most agree that routine screenings may help - and are unlikely to hurt.