Future Research
Colorectal cancer is the second leading cause of cancer-related death among US adults and is now the third most diagnosed cancer for people younger than 50 years, Dr. Grady said. Although overall CRC death rates have declined in recent years, the rates among those younger than 55 years have increased since the mid-2000s.
“When colorectal cancer is found earlier and the cancer has not yet spread throughout the body, patient outcomes are much better, as reflected in 5-year survival being much better. It makes sense that an effective blood-based test could have a potential role, in particular for those not getting screened yet,” said Joshua Melson, MD, AGAF, clinical professor of medicine and director of the High-Risk Clinic for Gastrointestinal Cancers at the University of Arizona Cancer Center in Tucson.
Dr. Melson, who wasn’t involved with this study, noted that blood-based testing shows promise for cancer detection but needs additional support for real-world implementation. For instance, the Shield blood test has difficulty detecting precancerous lesions, and it remains unclear what the optimal intervals for repeat testing would be after a negative test, he said. In addition, screening programs will need to ensure they have capacity to effectively deal with a positive test result.
“For a screening program to actually work, when a noninvasive test (whether blood-based or stool-based) is read as positive, those patients need to have a follow-up colonoscopy,” he said.
Proper communication with patients will be important as well, said Gloria Coronado, PhD, associate director of Population Sciences at the University of Arizona Cancer Center, Tucson. Dr. Coronado, who wasn’t involved with this study, has developed CRC screening messages for specific patient populations and studied patient reactions to CRC blood tests.
In a study by Dr. Coronado and colleagues, among more than 2000 patients who passively declined fecal testing and had an upcoming clinic visit, CRC screening proportions were 17.5 percentage points higher in the group offered the blood test vs those offered usual care. In qualitative interviews, one patient said of the blood-based testing option, “I was screaming hallelujah!”
“Patients believed that a blood test would be more accurate than a stool-based test. However, for the detection of advanced adenomas, the reverse is true,” she said. “It will be important to balance the high acceptance and enthusiasm for the blood test with the lower performance of the blood test compared to other tests already on the market.”
In a statement accompanying the study’s publication, the American Gastroenterological Association welcomed these results as an exciting development, but cautioned that a blood-based test was not interchangeable with colonoscopy.
“The Centers for Medicare and Medicaid Services (CMS) has determined it will cover a blood test for colorectal cancer screening every three years if the test achieves 74% sensitivity for CRC, 90% specificity, and FDA approval,” the statement reads. “However, a blood test that meets only the CMS criteria will be inferior to current recommended tests and should not be recommended to replace current tests. Such a test could be recommended for patients who decline all other recommended tests, since any screening is better than no screening at all.”
Dr. Grady is a paid member of Guardant’s scientific advisory board and advised on the design and procedure of the clinical trial and data analysis. Dr. Melson previously served as consultant for Guardant. Dr. Coronado reported no relevant disclosures.
A version of this article appeared on Medscape.com .