New blood tests are now available to screen for colorectal (colon) cancer, providing a simpler alternative to traditional methods. These tests only require a blood sample, sparing patients from the bowel preparation and discomfort of a colonoscopy.
While these blood tests sound appealing, they may not be as effective in catching cancer early, which is crucial for successful treatment.
A study from Stanford Medicine explored how these blood tests compare to colonoscopies and other screening methods. Researchers concluded that these new tests could be a good option for people who avoid other types of colorectal cancer screenings.
However, if people who would normally get a colonoscopy or stool-based test decide to switch to the blood test, more lives may be at risk.
This is because colonoscopies and stool tests are currently much better at detecting early cancers and polyps—small growths in the intestine that can turn into cancer over time.
By catching these polyps and early-stage cancers, traditional methods can prevent cancer from developing and spreading. Blood tests, for now, are less capable of detecting these early changes, and so fewer lives would be saved by using them instead of established methods.
According to Dr. Uri Ladabaum, a professor at Stanford and lead author of the study, blood tests are a promising development in colon cancer screening.
But he advises patients who are able and willing to take a colonoscopy or stool test to stick with those, as they are more reliable in catching cancer early.
Currently, about 4% of American adults will be diagnosed with colon cancer during their lives.
Early screening can help lower this risk. In the U.S., guidelines recommend that all adults aged 45 to 75 get screened for colorectal cancer, either by colonoscopy every 10 years or a stool test every one to three years.
A colonoscopy uses a camera to look inside the intestine and allows doctors to find and remove polyps before they become cancerous, making it a unique tool for both detecting and preventing cancer.
Despite its benefits, many people are either not getting screened at all or are not getting screened regularly enough.
To address this gap, new screening methods have been developed. In 2014, a stool test that looks for blood or cancer DNA was approved by the U.S. Food and Drug Administration (FDA).
This test can be done at home, and its convenience has encouraged some people to get screened. Recently, the FDA approved a blood test that detects tiny pieces of cancer DNA circulating in the blood.
Although this blood test is easier, it is not as effective at identifying polyps or early cancers, which limits its ability to prevent the disease.
Dr. Ladabaum’s team looked at the effectiveness of these blood tests by comparing them to stool tests and colonoscopies. They used existing data to estimate how each method might impact cancer rates in a large group of people.
According to their models, out of 100,000 people, those who undergo a colonoscopy every 10 years would see the lowest rates of colorectal cancer cases and deaths. For those who use stool tests every one to three years, cancer rates were slightly higher.
For the new blood tests, which are recommended every three years, cancer rates and death rates were two to three times higher than for colonoscopies. In fact, if everyone switched from colonoscopy to blood tests, more people could die from colorectal cancer.
The study also highlighted that colonoscopies and stool tests are more cost-effective than blood tests. This means that not only do the established methods save more lives, but they also save more money for the healthcare system.
Dr. Ladabaum emphasized that while blood tests are much better than no screening at all, encouraging people to switch from colonoscopy to blood tests could worsen health outcomes overall and drive up healthcare costs.
The researchers also looked at how people’s choices might impact overall cancer rates. Their ideal scenario is that people who currently use colonoscopy or stool tests continue with these methods. Blood tests should be reserved for people who avoid traditional screenings.
However, there is still uncertainty about how many people would opt for blood tests if offered, and whether they would follow up with a colonoscopy if the blood test shows a potential problem.
In the future, blood tests for colorectal cancer could improve, making them more competitive with colonoscopy and stool tests. For now, Dr. Ladabaum and his team hope patients and healthcare providers continue to prioritize the most effective screening tools available.
Increasing screening rates across the population is a goal, and it may require using a combination of different types of tests to reach more people.
This study included contributions from researchers at the University of Pittsburgh, the University of Washington, and the Oregon Health and Sciences University.
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The research findings can be found in the Annals of Internal Medicine.
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