Here is some good news for those of you who cringe at the thought of getting a colonoscopy: new research indicates that most colonoscopies will not be necessary in the future. Why is this? Well there have been two new DNA-based tests that claim to be able to detect colon cancer early. If this holds to be true, this will have a huge impact on reducing colon cancer. Colon cancer is a devastating disease that affects around 150,000 people a year in the U.S. and costs and astounding $14 billion to treat.
These new tests could allow the majority of people to bypass colonoscopies, which are currently recommended for people who are 50 and older. Instead of screening everyone, doctors may refer people for a colonoscopy only in cases where they have tested positive in one of the DNA tests.
It is believed that more people will go and get one of these DNA tests, because they are noninvasive in comparison to a colonoscopy, which uses a seeing tube that is fed threw the colon. These new tests could be available within the next two years.
In one of the test, created by Exact Sciences of Madison, Wisconsin, stool samples are examined to see if they contain the four altered genes that are characteristic of colon cancer. This test could find cancerous and precancerous tumors at an early curable stage that can be removed quickly.
The other test searches for changes in a single gene, called Septin 9, which is not one of the Exact Sciences’ panel of four genes. Epigenomics AG in Germany developed this test.
The good news is that both of these tests would be less costly than a colonoscopy and perhaps even more effective. The first test, which examines stools, will cost around $300. The current average cost of a colonoscopy is around $2000. A lot of people tend to avoid colonoscopies because they are invasive, and the general cost per detection is high since most people are in pretty good health. They also miss many tumors in the upper part of the intestine.
Exact Sciences has decided to sign up several thousand patients in a future trial that they hope the FDA will approve. The trial will be finished in 2012 and the test will be available soon after that, as long as it is approved.
Dr. David Ahlquist from the Mayo Clinic, who is an adviser to Exact Sciences, said “If widely used, and regularly, this test really does have the opportunity to eliminate colon cancer.”
Of course, the value of the tests depend heavily on details such as their sensitivity, which means the proportion of detected tumors and their specificity, or how many of the positive results are false alarms. In July, Exact Sciences claimed that its test was extremely sensitive and specific when applied directly to cells taken from tumors. In reality, the tumor DNA has to be detected in stool samples. This is a much harder to accomplish, because almost all the DNA comes from the bacteria of the gut, and only 0.01 percent of the DNA in feces is human. In October, the company revealed at a meeting of the American Association for Cancer Research that in a trial of 1,100 patients, the test detected 64 percent of polyps, larger than 1 centimeter in diameter, and 85 percent of cancers, as judged by the colonoscopies that were also performed on the patients.
Dr. Ahlquist is happy with the results, particularly the 64 percent detection rate for precancerous polyps.
Even though this detection rate seems less than perfect, it will be highly effective is the test is performed on a regular basis. Ahlquist said that “The pap smear detects only 50 percent of cervical cancers, but applied over time it virtually eliminates the disease.”
The Exact Sciences test specificity is 88 percent. This means that 12 percent of the time a patient will be given a false alarm. This may not be so bad, since the worst that will occur is that the patient will have to undergo an unnecessary colonoscopy.