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Despite the conflicting headlines and misinterpretations of a new study, colonoscopy is still the most recommended screening method for colorectal cancer.

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A study recently published in a high-profile medical journal seemed to question the effectiveness of colonoscopy, a proven and widely used strategy for screening and prevention of colorectal cancer.

The news headlines were noteworthy: “Disappointing results on colonoscopy benefits”; “New study suggests benefits of colonoscopies may be overestimated”; “In the gold standard trial, invitation to colonoscopy reduced cancer incidence, but not death.”

Such news has sparked controversy and created some confusion about the study and its results, leading people to question whether the results warrant a reassessment of benefit and the need for a colonoscopy.

As a cancer research scientist with over 20 years of experience in colorectal cancer screening and prevention, I am confident that colonoscopy remains one of the most critical and effective tools for screening, detecting and preventing this common and deadly form of cancer.

Colorectal cancer is the fourth most common and second leading cause of cancer deaths in the United States. The American Cancer Society estimates there will be 151,000 new cases of colorectal cancer and approximately 53,000 deaths in 2022. Screening has contributed to a marked decline in colorectal cancer cases and deaths over the past few decades.

Current US Preventive Services Task Force guidelines recommend that people at average risk begin screening for colorectal cancer at age 45. This recommendation was lowered from age 50 in 2021 due to the recent increase in the prevalence of colorectal cancer disease among young adults.

Unpacking the new work

Various studies have shown that colonoscopy screening is highly effective in detecting and removing precancerous polyps before they progress to cancer.

That’s why media coverage of the new study, published in the New England Journal of Medicine, has sparked confusion and concern among healthcare professionals and the public. Many of these news reports misinterpreted the study as showing that colonoscopies had a small effect on the incidence of colorectal cancer and were ineffective in reducing deaths. Such misinterpretations can have serious consequences for efforts to screen and prevent a type of cancer that affects the health and well-being of many.

In the study, a team of European researchers conducted a randomized clinical trial that examined the risk of colorectal cancer and death in healthy men and women aged 55 to 64 years. Study participants collected from census records in Norway, Sweden, Poland and the Netherlands were either invited or not invited for colonoscopy and received usual care.

About 10 years later, the research team collected information on the incidence and deaths of colorectal cancer of 28,220 in the invited group and 56,365 in the uninvited group. They found that those in the invited group had only an 18% reduction in the number of colorectal cancer cases compared to those in the uninvited group. They also found that there was no significant reduction in deaths in the invited group. This seemingly disappointing result led to more and more misleading headlines in the media.

But there is a critical caveat in all of this that is worth explaining. Only 42% of participants invited to have a colonoscopy did so. This proportion ranged from 33% among those from Poland, where most of the respondents were recruited, to 60.7% among those from Norway.

When the researchers determined the benefit among those who actually had colonoscopy, they found that the incidence of colorectal cancer was reduced by 31% and deaths by 50% – results much closer to what would be expected from other studies.

Another shortcoming of the study is the time between recruiting and screening participants. Colorectal cancer is usually slow to develop and takes 10 or more years to progress from precancerous polyps to cancer. Therefore, the 10-year timeframe used in the study may be too short to quantify the full impact of colonoscopy screening. The authors are aware of this and state that they will conduct an analysis every 15 years.

These and other issues have been articulated in responses to the study by various medical and advocacy groups of experts with long experience in colorectal cancer and screening. These include the National Colorectal Cancer Roundtable, the Colorectal Cancer Alliance, the American Cancer Society, and the American Society for Gastrointestinal Endoscopy.

All responses highlight that, despite the tone of much of the media coverage, nothing in the study changed the known reliability or effectiveness of colonoscopy screening. At best, the findings confirm that for many, a simple invitation to screening does not necessarily encourage participation.

Colonoscopy remains the ‘gold standard’

During colonoscopy, a long flexible tube is inserted into the rectum and moved through the colon to allow direct visualization, identification, imaging, and removal of abnormal tissues such as precancerous polyps that may progress to colorectal cancer. For this reason, colonoscopies for some time were and still are considered the “gold standard” for colorectal cancer screening and prevention.

However, the procedure has a few features that might deter people from choosing it. It is invasive and has a small risk of complications. Additionally, for the procedure to be effective, the colon must be cleansed of any stool, requiring a protocol that many find unpleasant and irritating. Finally, it can be expensive and creates barriers for those who do not have adequate insurance coverage.

While not as sensitive as colonoscopy, there are a number of non-invasive alternatives currently available for colorectal cancer screening, recommended by the US Preventive Services Task Force for people at normal risk. Such alternatives include stool tests such as high-sensitivity guaiac stool occult blood tests, stool immunochemical tests, and multi-target stool DNA tests.

The effectiveness of these methods varies, and each has its advantages and disadvantages. The choice of choice is based on patient preference as determined by input from the medical provider. However, those at higher risk are recommended to be screened with colonoscopy, such as a family history of colorectal cancer, certain symptoms such as blood in the stool or a history of polyps.

More importantly, noninvasive screening tests alone do not prevent disease. Rather, they increase the likelihood of the presence of a benign polyp or tumor and therefore should be followed up with a colonoscopy to confirm the presence and remove any abnormal lesions.

New guidelines for cancer screening

Recently, researchers have made significant progress in developing liquid biopsies that involve profiling informative biomarkers in fluids such as blood. This type of profiling identifies signals to detect and monitor a large number of cancers, including colorectal cancer.

There is particular enthusiasm in the scientific and medical communities for liquid biopsies, which can aid in the early detection of multiple cancers. This approach offers great potential in the early detection of colorectal cancer and many other cancers for which effective screening methods are currently lacking. Multiple cancer early detection tests are being developed by many companies and have not yet been approved by the Food and Drug Administration. Many are currently available by prescription as lab-developed tests.

As with all non-invasive testing, liquid biopsies should be followed appropriately to confirm, excise, and/or treat identified lesions. Extensive research on liquid biopsies is ongoing, and the results indicate that the next generation of highly sensitive, readily available and patient-friendly cancer screening modes will emerge in the next few years.

Over the past few decades, screening has contributed significantly to a marked reduction in the incidence and mortality of colorectal cancer. Given the aging of the population and the recent increase in colorectal cancer among young adults, it is more important than ever to detect the disease precisely and in its earliest stages.

This article has been republished from The Conversation, an independent non-profit news site dedicated to sharing the ideas of academic experts. Posted by Franklin G. Berger, University of South Carolina. The Conversation has a variety of fascinating free newsletters.

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Franklin G. Berger receives funding from the Centers for Disease Control and Prevention

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