At the beginning of the annual meeting of the American Society of Clinical Oncology in Chicago last week, Grail unveiled the first data on its system for the early detection of cancers using a blood sample.
The data were early – with 2,508 out of the 15,000 patients in the company’s trial – but promising, showing a 99 percent sensitivity rate and a 1 percent false-positive rate that the company said is likely to go down in the long run.
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However, one industry executive said even a 1 percent false-positive rate could become problematic in larger populations of patients. “One percent in a patient population of 5,000 is manageable,” said Joydeep Goswami, president for clinical next-generation sequencing and oncology at biotechnology product development company Thermo Fisher Scientific, in an interview at the ASCO meeting. “With 1 percent in hundreds of thousands or millions, you quickly get into different dynamics.”
That, in turn, could create cost-effectiveness issues, as patients who get false-positive results would be subjected to a battery of tests afterward, Goswani said.
In an email, Grail spokeswoman Kelsey Grossman reiterated that the actual false positive rate may be less than 1 percent, as cancer incidence rates suggest some people enrolled in the non-cancer group may have had an undiagnosed cancer. “We believe it is critically important that an early detection test have a very low rate of false positive results (high specificity) to minimize unnecessary follow-up, anxiety and potential harms from a diagnostic workup among patients,” Grossman wrote, noting that the 1 percent rate is still lower than some current cancer screening modalities.
An approach to using blood tests for early detection that makes sense for now is to target at-risk individuals, such as smokers and those living in environmental circumstances that could be carcinogenic, Goswami said. Dr. Julie Lang, director of the breast cancer research program at the University of Southern California’s Keck School of Medicine, concurred. A 1-2 percent false-positive rate may or may not be problematic based on clinical circumstances, but would be totally acceptable for lung cancer patients. “If the Grail test is used as evidence to pursue further imaging or endoscopy and if needed obtain tissue diagnosis, then no harm would come to the patients from the 1-2% false positive rate,” she wrote.
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Lang wrote that the numbers for Grail’s test will likely continue to improve with increased numbers of patients given that the test relies on machine learning. Still, both she and Goswami agreed that another risk of a false-positive result could be psychological. Patients will need to be informed of the potential risk of false-positive results and implications of possible further testing. “Some patients might experience significant anxiety from being told they had a positive test but in fact they were negative,” Lang wrote. “That is the potential harm of this test – psychological distress, unnecessary imaging and perhaps invasive biopsies.”
Photo: Alaric DeArment, MedCity News