Kristine M. Conner
University of Pennsylvania Cancer
Ultima Vez Modificado: 15 de mayo del 2001
"The best screening test is the screening test that gets done."
That was the central point repeatedly made by Sidney Winawer, MD, Chief of Gastroenterology at Memorial Sloan Kettering Cancer Center, as he sketched out a twenty-five year history of developments in colorectal cancer screening on the final morning of ASCO 2001. Winawer's presentation was given as part of a ceremony honoring him as this year's winner of the American Cancer Society Award.
Dr. Winawer has made outstanding contributions to the medical community's knowledge of how to screen for, prevent, and treat colorectal cancer, and he recently was part of a committee of experts who authored a global statement on preventive strategies such as lifestyle changes and screening. He's also no stranger to the distress and anxiety that a cancer diagnosis can cause. In his 1998 book Healing Lessons, Dr. Winawer tells the story of his wife Andrea's three-and-a-half year struggle with advanced stomach cancer and its impact on him and the entire family.
Winawer's talk focused on the importance of making the public at large understand colorectal cancer as a preventable disease. For nearly thirty years now, he noted, researchers have known that non-cancerous adenomas, better known as polyps, develop into colorectal cancer over a period of time. This "adenoma-carcinoma sequence" makes it possible to prevent the disease by finding and removing polyps.
"We have a large window of opportunity to intervene in the disease process," Dr. Winawer stressed to his audience again and again. In many cases, there is as much as a ten- to fifteen-year gap between the time a polyp appears and it develops into cancer, he said. The familial syndromes are an exception, with adenomas typically developing into cancer very quickly and at a very young age. But roughly 70 percent of colorectal cancer cases are not associated with these syndromes, and many could be prevented even by relatively infrequent screenings?every five to ten years, depending on the test that is done, versus the annual or biennial screenings that are recommended for other forms of cancer.
Current guidelines recommend that men and women over age 50 (and those over 40 with a family history of polyps or colorectal cancer) have a fecal occult blood test every year and flexible sigmoidoscopy every five years, OR a full colonoscopy every ten years. (Sigmoidoscopy images only the lower part of the colon.) All of these tests have been around since the 1970s, Dr. Winawer said, and all three have been proven to reduce the incidence and mortality of colorectal cancer. When a colonoscopy is done, any polyps that are found can be removed right away. The former tests, if positive, would be followed by a colonoscopy and removal of any lesions that are found.
Dr. Winawer pointed to a number of trials of fecal occult blood testing that have shown a roughly 20 percent reduction in mortality with biennial screening (with a series of samples being taken for testing, rather than just a one- time sample). He also mentioned two trials that have shown a 30 percent and 40 percent reduction respectively in colorectal cancer mortality as a result of sigmoidoscopy screening. Conventional wisdom suggests that colonoscopy is the best screening test because it images the entire colon, although no clinical trials have actually compared it to the other methods. And Winawer stressed that such a trial may never get done, simply because colonoscopy is so widely accepted at the best test.
But the "best test," he asserted, is any test that gets done. And it may very well be that even less frequent screening is sufficient to impart benefit. In fact, current clinical trials are looking at whether one-time colonoscopy with removal of any polyps found might afford protection that is equal to more frequent screening. Removing polyps causes a decrease in risk that endures, Winawer said, and it may be that intervening just once in a person's life is enough.
However, the key challenge now is getting the public to understand that colorectal cancer is a preventable disease. "Polypectomy prevents cancer," Dr. Winawer said. "We all know that, but we have to tell the public."
"We have the technology, but now we have a major battle, a major mountain to climb," he added. "And that is implementation."
A recent American Cancer Society survey suggested that physicians may be part of the problem. One of the most common reasons that people gave for not getting screened was that it was "not recommended by my doctor." Winawer pointed out that failure to screen is leading to more and more litigation, with colorectal cancer patients and their families suing physicians for deviating from what's now considered the standard of care. "It's becoming increasingly difficult to defend a physician who does not screen for colorectal cancer," he stressed.
By the year 2005, the American Cancer Society aims to have 75 percent of people in the target group (men and women over 50, those over 40 with a family history) aware of colorectal cancer screening, and 60 percent actually having it done. These goals should be helped along by recent legislation requiring Medicare reimbursement for the available screening tests, Winawer said. They should also receive a boost from public awareness campaigns such as that launched by Katie Couric and the designation of March as Colorectal Cancer Awareness Month.
Winawer cautioned against putting too much faith in screening tests that seem promising but have not yet been proven, such as DNA analysis of stool samples and virtual colonoscopy. While these new, less invasive options are exciting, they shouldn't be seen as an excuse to put off testing until something better than fiber-optic colonoscopy comes along. In fact, virtual colonoscopy can be very uncomfortable, because it involves filling the bowel with air without the benefit of sedation. It is also extremely labor- intensive and involves a real learning curve since it's so new. Rather, Winawer suggested, the mindset must be that we already have the tools available to prevent this disease.
"Right now we have the technology and the understanding," he said. "We can intervene in the progression that we know is associated with colon cancer and make a real difference in people's lives?now, here, today!"