"We found the Septin9 gene methylated in over 90 percent of colorectal cancers, but not in healthy tissue and not in other cancers," Dr. Plum says. "When we discovered it we were intrigued by this specific marker."

Dr. Plum is quick to point out that the Septin9 detected by the tests is not found within free-floating cancer cells in the bloodstream, but is actually "naked DNA" shed by the often unstable tumors in the gut. Generally, this would make it hard to pick up amidst the noise of other, normal DNA swimming in the blood. But Dr. Plum says colorectal cancer's methylation pattern is so specific, it makes it possible for them to be confident about the origin of the gene.


While Dr. Plum says they found the methylated Septin9 gene using a statistical approach, there could be a good biological reason for this to be linked with cancers. "We know already from academic research that it lends itself to the idea that it's some kind of tumor-suppressor gene," he says. "There are certain indications that it regulates growth of cells."

FAIRLY SENSITIVE

But the real test of the test is how many cancers it can catch early enough for them to be treated in time.

Quest's Bost says previous clinical studies of around 3,000 samples suggest it can detect around 70 percent of colorectal cancers at about 90 percent specificity.

Dr. Plum says they don't expect the findings from the PRESEPT trial to be any different, although he says the sensitivity could appear to be somewhat lower. In a screening program, most of the patients will be asymptomatic and thus, if they have cancer, they have early stage cancers, the hardest to detect.

"We could detect around 50 percent of stage 1 cancers, and for stage 2 and 3, 75-85 percent," Dr. Plum says, of earlier studies.

The current guidelines by the American Cancer Society require non-invasive tests for colorectal cancer screening to be at least 50 percent sensitive for the cancer at the time of testing, a goal Dr. Plum says he expects the blood test to surpass.

COMPLIANCE, NOT PERFORMANCE

But Dr. Plum says the main obstacle to successful screening of colorectal cancers isn't the sensitivity of tests, but rather the reluctance of people to undergo them.

"Our blood test is comparable to the best stool based methods out there, such as the more advanced stool DNA testing," he says. "The only problem is, all these advanced stool methods never increased compliance. It's not a performance game, it's a compliance game."

Or as one of the opinion leaders in the field once told Dr. Plum, "It's very simple. The best test is the one that gets done."


Back to HCB News

More Industry Headlines