NEW YORK (360Dx) – In the fight against colorectal cancer (CRC), there is perhaps no better tool than an accurate diagnostic test that can catch possible malignancies in their early stages to allow doctors to either remove polyps or watch them to see if they'll progress to later-stage disease. Right now, the choices for most people are limited to colonoscopy or using Exact Sciences' at-home stool test Cologuard.
But thanks to new research from a team at the University of Wisconsin-Madison, there may soon be a blood test for colon cancer.
Until recently, the earliest and most accurate way to detect cancer in the colon was with a colonoscopy. But even though it's the gold standard diagnostic, the preparation needed to undergo the procedure, the risk of undergoing anesthesia, and the general discomfort involved makes some patients reluctant to comply with the five-to-10-year testing schedule.
Exact Sciences became the first firm to offer a different option five years ago with a breakthrough test that allowed for the screening of cancer in stool samples. The conventional wisdom until then had been that there was so little human DNA in stool that it would be impossible to check for the genetic mutations that are indicative of cancer.
The firm's Cologuard test enables patients to collect their own samples and send them to Exact's lab for processing. It obviates the need for the fasting, intestinal cleansing processes, trips to the hospital, and anesthesia that can be a part of colonoscopies. The test itself — which was developed in collaboration with the Mayo Clinic — is an automated assay for tumor-specific DNA changes, including aberrant methylated BMP3 and NDRG4, a mutant form of KRAS, beta-actin, and hemoglobin.
Not surprisingly, however, Exact's success has attracted the attention of potential competitors. In February, privately owned Italian company Diatech Pharmacogenetics — which bills itself as the owner of more than 70 percent of the Italian molecular diagnostic market — released its own stool-based CRC diagnostic kit. Diatech's test searches stool samples for fragments of long DNA — pieces of DNA that are 200 basepairs or longer and which characterize non-apoptotic DNA that has been shed into the fecal stream from diseased mucosa — as a biomarker for early diagnosis of CRC.
That company's test isn't something a patient could do at home and it has to be paired with fecal occult blood testing in order to provide maximum benefit, so it isn't directly comparable to Cologuard. But, its stool-based, noninvasive nature positions it as a possible competitor to Exact's test if Diatech gets regulatory approval in the US.
In St. Louis, startup Geneoscopy is also developing an at-home stool-based CRC test. The company's CRC diagnostic kit is modeled on Cologuard, but it looks for RNA biomarkers in stool rather than DNA biomarkers. That difference, according to Cofounder Erica Barnell, means that Geneoscopy's test is much better than Cologuard at detecting high-risk adenomas.
More recently, researchers at Obafemi Awolowo University in Nigeria, Memorial Sloan Kettering Cancer Center, and the University of Alberta began working to develop a urine-based point-of-care handheld diagnostic device that looks for a specific metabolomic signature to screen patients and determine their risk for developing CRC. This device isn't meant to replace more conventional testing modalities like colonoscopy, but rather it is meant for use in low- to middle-income countries where such testing resources are limited. The metabolic signature can indicate whether a patient is not in danger of developing CRC or should be referred for further testing with colonoscopy.
If all goes according to plan, UW-Madison's blood-based test may offer yet another modality for colon cancer testing.
In a study in the Proceedings of the National Academy of Sciences, researchers led by UW-Madison professor of oncology and genetics William Dove reported that they were able to detect protein signals in the serum of patients carrying an adenoma as small as six to nine millimeters, and were also able to find these four protein markers — F5, ITIH4, LRG1, and VTN — in patient blood samples regardless of the total volume of the adenomas these patients carried.
Dove and his colleagues discovered the serum protein biomarkers in rat and mouse models of early colonic adenomagenesis, which they created through mutagenesis. They then studied the biomarkers in patients using quantitative mass-spectrometric assays. One cohort included patients with adenomas that were known to be growing based on longitudinal computed tomographic colonography. The other cohort, screened by optical colonoscopy, included patients who were free of adenomas and patients who had adenomas and whose risk status was judged by histopathology.
The researchers found that levels of the F5, ITIH4, LRG1, and VTN markers were each elevated in the patients and in the rat model, and noted that the elevated level of each of the markers was correlated with the number of colonic adenomas in the rat model. However, the levels of the markers in the patients were not significantly correlated with the total adenoma volume.
Further, they found that elevated levels of these four markers persisted in the blood samples of patients after polypectomy. Two additional serum markers, growth-associated CRP and PI16 rapidly renormalized after polypectomy. Growth-associated CRP levels were enhanced only with high-risk adenomas while PI16 levels were reduced regardless of risk status and were not associated with growth, the team reported.
"When we studied the tumors longitudinally in these virtual colonoscopy patients … we knew what the size of the adenoma was when the blood sample was taken. And because these were quantitative mass spectrometry assays, we knew the magnitude of the signal. And it turned out that the magnitude of the signal was not at all correlated with the volume of the adenoma," Dove said. "We were able to have rats with two tumors, four tumors, 10 tumors in the colon. The signal was correlated with that number.
"But in the patients where we knew the size, it wasn't correlated with the total volume. So, the logical corollary of that is that these markers detect tumors of any size, will detect the nascent tumor or the full-blown tumor," he said.
In their study, the researchers set out different hypotheses as to why these particular markers created such a strong signal. One idea is that they signal the host's response to the nascent adenoma. The response could be local, in the formation of the stroma surrounding the tumor; distal, as from the host liver; or systemic, as with mediators of the immune response or the repair of epithelial wounding associated with the nascent adenoma. In this hypothesis, the four markers would be involved in the repair of epithelial wounds that remain after polypectomy, the authors wrote. They also questioned whether the serum markers are specific to the early development of adenomas or only to colon cancer.
These questions, and others, will most likely have to be explored and answered before this discovery can be turned into an actual blood test. But the potential for a new diagnostic is high, and it could fill in existing gaps in the testing landscape.
"This [test] would be basically supplemental, because these [markers] are a two- or, at most, fourfold signal to noise," Dove said. "First this would become appropriate on the front burner for patients known to be at risk, for example ones who had had polyps before and had them removed. Those [patients] are more at risk for new polyps."
He also noted that as good as Madison, Wisconsin-based Exact's Cologuard is, the test's efficiency for detecting advanced adenomas is about 40 percent, at best.
"It has value, but it's not sufficient. Nor are any of the markers we're talking about, but they are addressing that class of growing pre-malignant adenomas to try to fill that gap," he added. "[In the future], we hope that there will be a combination of markers that, together, will be powerful enough in their signal to noise and can be multiplexed."
The biggest advantages of a possible diagnostic to come from this research may be its sample type: blood. Dove noted that the markers could even be integrated into general blood tests and carried out in various parts of the world, and then sent to specialized labs like the ones in Madison for specific analysis of the four protein markers.
Further, blood is easier to work with than stool, which can be tricky to analyze. Exact requires that all Cologuard kits be sent to its central testing lab for analysis in order to ensure accurate results. That may not be necessary with a blood test, which could be analyzed at a hospital or clinic lab.
As of now, the Wisconsin Alumni Research Foundation — a nonprofit organization affiliated with UW-Madison that aims to help the university's researchers commercialize their discoveries — has applied for patent protection on the animal models described in the study, Dove said. However, the models are available for use by any research lab for cancer research.
Further, he and his colleagues are in early discussions to begin development of a blood-based diagnostic, though he couldn't elaborate on any details.
"In a way, this publication has a very modest discovery," Dove noted. "Still, it has these elements that can be multiplied in other contexts and multiplied in the context of colon cancer by giving this small signal that separates the growing pre-malignant tumor from the static and regressing one."