Blood Test for Colorectal Cancer: The Last Resort?

Roxanne Nelson, BSN, RN

August 31, 2016

Despite recommendations, many Americans in the target age group are not getting screened for colorectal cancer.

However, a new blood-based screening test may help boost those rates because of its simplicity and convenience for the patient.

The downside is that the new test is not as sensitive or accurate as a colonoscopy or the other recommended screening approaches.

Approved in April 2016, the Epi proColon (Epigenomics AG) is the first blood-based colorectal screening test to get a thumbs-up from the US Food and Drug Administration (FDA).

This molecular test detects methylated Septin 9 DNA in plasma, which is increased in colorectal cancer and can be found in tumor DNA that has been shed into the bloodstream from both colon and rectal sites. This makes it a differential biomarker for the early detection of colorectal cancer, according to the manufacturer.

Available in Europe since 2012, it is also being marketed in other countries, including China.

The question now facing healthcare providers is, Where does this new test fit in the current armamentarium of screening options?

"It's the new kid on the block, another alternative, and one that isn't as highly recommended as the current options that are available," said Andrew Chan, MD, an associate professor of medicine at Harvard Medical School and a practicing gastroenterologist at Massachusetts General Hospital in Boston.

The major advantage of the Epi proColon is that because it is fast, easy, and noninvasive, it may appeal to individuals who have shunned other screening approaches.

"I believe that any screening test is better than no screening," Dr Chan told Medscape Medical News. "But we also have to be cautious about using screening tests simply because they are easy to employ. Screening also involves a follow-up and a discussion of the results."

What isn't clear is whether the benefits outweigh the risks, he explained. "Or if there are tradeoffs, such as the test picking up false-positives or the consequence of false-negatives, which may give the patient an inappropriate sense of security."

Basically, there are a lot of caveats with this test, and it shouldn't be considered an easy alternative. "This blood test hasn't been shown to reduce mortality from colon cancer, which is the most important data," Dr Chan emphasized. "So we don't know how it is going to compare to the other established screening tests."

Need for More Options

Both the incidence of and mortality from colorectal cancer have been declining in recent years, and much of that is attributed to screening.

However, screening rates are well below the targets designated by public health agencies. According to National Health Interview Survey data, screening use overall was below the targets; there were no improvements from 2010 to 2013 for not only colorectal cancer screening but also for breast and cervical cancer.

But for colorectal cancer screening, after adjustments were made for age, 58.2% of survey respondents aged 50 to 75 years reported getting screened.

This rate falls short of the Healthy People 2020 target of 70.5% (2008 baseline, 52.1%). In addition, screening was lower among Asians and all Hispanic subgroups except Puerto Ricans, and younger individuals were less likely to be screened (50 to 64 years, 52.8%) compared with older persons (age 65 to 75 years, 69.4%).

"Anything that brings more people into screening is great," commented David Johnson, MD, a past president of the American College of Gastroenterology (ACG) and coauthor of the ACG's colorectal cancer screening guideline. But this new blood test "is not meant to replace any of the better tests that are available now, and that is the undercurrent message."

The Epi proColon is primarily meant for people who have declined other types of screening, he told Medscape Medical News. "This is a test that only detects cancer, and the best test should be able to prevent cancer, and recognize precancerous polyps."

The ultimate screening test should mitigate toward cancer prevention rather than detection, explained Dr Johnson, who is also professor of medicine and chief of gastroenterology at Eastern Virginia School of Medicine, Norfolk.

Colonoscopy has been proven to decrease the incidence of colon cancer and prevent colon cancer-related death, and it remains the preferred strategy in the ACG's guidelines, last published in 2009, he noted.

"It is the best test is to prevent cancer because it can detect polyps and in turn decreases mortality and colon cancer incidence," he said. "For every 1% in adenoma detection rate, there was a 3% reduction in the incidence in colon cancer and a 4% reduction in death, and it comes down to polyp removal."

All of this needs to be put into context in primary care, where most patients will most likely be counseled about screening. "In primary care, when patients ask about the Epi proColon, it should be put into context as to how it compares with other tests," he said. "And importantly, that the test is just for cancer detection and will not detect precancerous polyps."

The Centers for Disease Control and Prevention, in conjunction with other groups, has set a goal for a screening rate of 80% by 2018 in order to reduce colon cancer incidence and death rates.

"This test could help reach that goal," Dr Johnson said. "But only if the patient has been appropriately counseled and refuses everything else, then this becomes an option. It is paramount that the provider puts it into perspective."

Task Force Guidelines

In their updated 2016 guidelines, the US Preventive Services Task Force (USPSTF) found convincing evidence that colorectal cancer screening substantially reduces disease-related mortality, but it did not recommend any one screening approach over any other.

The USPSTF now recommends seven different screening strategies: colonoscopy, fecal immunochemical testing (FIT) for occult blood, guaiac-based fecal occult blood testing, sigmoidoscopy alone, sigmoidoscopy plus FIT, the FIT-DNA test, and computed tomographic colonography.

They all have varying levels of evidence supporting their effectiveness, and the potential harms also differ among the specific approaches.

Douglas Owens, MD, former Task Force member, general internist at the Veterans Affairs Palo Alto Health Care System, and professor at Stanford University in California, pointed out that the Epi ProColon test was included in the Task Force's review.

"This screening method currently has limited published evidence evaluating its use," he said. "It had a sensitivity to detect colorectal cancer of under 50%, which is quite low, as we would want sensitivity levels at about 90% or higher. Therefore, it was not included in the table on screening strategies in the final recommendation statement."

Dr Owens emphasized that the FDA recommends that the blood test to detect methylated SEPT9 DNA be offered only to patients who have a history of not completing colorectal cancer screening.

"The FDA also recommends that the available tests included in the Task Force's 2008 final recommendation be offered first," he said. "The Task Force bases all of its recommendations on the best evidence that is currently available. As such, the tests with sufficient evidence were listed in the table."

Efficacy of the Test

Two years before the FDA approved the blood test, the Molecular and Clinical Genetics Panel of the FDA's Medical Devices Advisory Committee reviewed the data. Even though the reception was not overly enthusiastic, they voted by a narrow margin to recommend premarket approval for the test.

Most of the panel agreed that the test was safe (yes, 9; abstain, 1).

But when it came to effectiveness, the panel was decidedly mixed (yes, 5; no, 6), as well as regarding whether its benefits outweigh its risks (yes, 5; no, 4; abstain, 1).

Data from two clinical studies were used in the decision making process.

The first study compared the efficacy of Epi proColon to colonoscopy in 1544 samples drawn from individuals aged 50 to 85 years who were at average risk for colorectal cancer.

The sensitivity of Epi proColon was 68.2% (95% confidence interval [CI], 53% - 80%) and specificity was 80% (95% CI, 77.9% - 82.1%). The negative predictive value was 99.7% (95% CI, 99.6% - 99.8%) and positive predictive value was 2.4% (95% CI, 2% - 3%).

The second study compared the accuracy of Epi proColon to FIT using matched blood and stool samples from 290 participants. Epi proColon was statistically noninferior to FIT with respect to sensitivity (72.2% for Epi proColon vs 68% for FIT) but not specificity (80.8% vs 97.4%).

The manufacturer does agree that the Epi proColon test is not meant to be a simple alternative to the other screening strategies — at least not at this time.

Instead, the company emphasizes that the test is indicated for people who are at average risk for colorectal cancer, are age 50 years and older, and have been offered and have a history of not completing screening by tests recommended in the 2008 USPSTF guidelines.

These recommended tests should be offered and declined before Epi proColon is offered as an option for screening, and specifically, the Epi proColon is not intended to replace screening tests recommended by appropriate guidelines, the company emphasizes.

"There are 23 million average risk people who are not getting screened," said Noel Doheny, CEO of Epigenomics USA. "And those are the people we are targeting."

The assumption was that people who were unwilling or unable to undergo screening with the recommended tests might do so if an easier option was available. "The third study we did is pending publication, and it answered the question for the FDA — would somebody who is noncompliant use a blood test," he explained. "We recruited 413 patients who were twice noncompliant after being told by a physician to get either a colonoscopy or FIT, and 99.5% of those randomized to our test got a blood test on the spot."

Of 203 individuals in the Epi proColon group, 202 had the test done. Of that group, 30 had a positive test result; of those, 17 individuals went on to have a colonoscopy, with 10 having a polyp removed.

In the FIT group, of the 210 participants who were offered the stool test, 185 completed it (88.1%). There were 3 positive results, and 1 person had a colonoscopy with a polyp removed.

"Participation is the key," said Doheny. "If you can't get someone tested, the specificity and sensitivity aren't of any value. But by getting 99.5% tested, you can now answer those questions for those who were previously noncompliant."

These are the only data available right now, but he explained that his company is currently in a dialog with the FDA about postapproval studies.

"We are planning trials that will confirm the adherence number and look at the test's usage over a number of years," he said.

In addition, there are also trials in place with high-risk patients, and a similar trial in lung cancer has been initiated.

Regarding insurance coverage, Doheny pointed out that the Epi proColon test was actually available for several years before its FDA approval.

"The test was developed over 4 years ago with the help of Quest Diagnostics and ARUP [Associated Regional and University Pathologists] as a laboratory developed test," he said. "They configured it and offered it, and over the years, a majority of payers have been paying for it."

"Since we received approval, the number of payers is now likely to be even higher," Doheny added.

The test still has yet to be approved for insurance reimbursement by the Centers for Medicare & Medicaid Services (CMS), but the company is currently in discussions with CMS.

Dr Johnson disclosed that he has served as a director, officer, partner, employee, advisor, consultant, or trustee for Pfizer Inc, Epigenomics, WebMD, CRH Medical, and Medtronic and has received income in an amount equal to or greater than $250 from Pfizer Inc, Epigenomics, WebMD, CRH Medical, and Medtronic. Dr Chan reports consulting for Bayer Healthcare, Pfizer Inc, and Pozen Inc.

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