Guardant Health is working to move blood tests for early cancer detection from development into broader clinical use, building on the Shield test, which detects cancer-related signals from DNA released by cells into the bloodstream. The test is intended to detect disease before symptoms appear, when the chances of treatment are better, but it does not eliminate the need for colonoscopy or serve as a replacement for it.
In an interview with MedTech Dive, Sam Asgarian, vice president of clinical development at Guardant Health, said the company has already administered Shield tests to hundreds of thousands of people since it entered use during 2025. The company estimates that about 54 million people in the United States have not undergone colorectal cancer screening or are overdue for screening, meaning the test’s current reach remains far from covering the target population.
A Test Targeting People Who Have Not Been Screened
Shield’s greatest use appears to be among people who have not previously undergone screening. According to Asgarian, physicians offer the test to patients who do not necessarily refuse screening but hesitate to undergo colonoscopy or do not consider themselves at risk. The company believes a blood test may add a practical option for this group rather than leaving it unscreened.
In 2024, Shield received approval from the U.S. Food and Drug Administration, FDA, for use in people aged 45 and older who are not classified as being at high risk of developing the disease. However, the FDA emphasized the test’s limitations in detecting stage 1 cancer and precancerous lesions, so colonoscopy remains necessary, particularly when a result is positive.
Guardant says that more than half of patients who received a positive result subsequently underwent colonoscopy as well. The company wants to collect more data over the next year to measure how many people Shield actually encouraged to complete the screening process, as well as its contribution to reaching people who had previously refused colonoscopy.
Limitations of the Current Generation and Plans to Improve It
A study published in the New England Journal of Medicine found that Shield failed to detect 16.9% of cancer cases, and its sensitivity for detecting advanced precancerous lesions was low, at 13.2%. Asgarian says that all of the cases the test failed to detect were stage 1, while the current FDA approval does not include detection of precancerous lesions.
The company is working on a new generation that will increase the test’s sensitivity, focusing first on improving detection of stage 1 cancer and then on increasing its ability to detect precancerous lesions. Guardant partly explains this limitation by noting that these lesions do not release enough detectable material into the bloodstream, and may not release any at all. Asgarian aims to raise sensitivity for these lesions to a level in the high teens, approaching the performance of some stool-based tests, whose rate is in the twenties.
Alongside DNA signals, the company is investigating other substances released by cells, such as fats, proteins, RNA and other metabolites, in the hope that combining these indicators will improve performance. Guardant has also received approval for a version with higher processing capacity that allows the laboratory to process a larger number of tests. If the laboratory trials are successful, Asgarian expects an improved version to be ready for submission to the FDA within one to one and a half years, with the timeline extended by approval requirements.
From Colorectal Cancer to Multicancer Screening
Guardant is expanding the technology into a multicancer test covering 10 types, including breast and colorectal cancer, as well as types for which broad routine screening is not available, such as pancreatic and ovarian cancer. The test is performed for the patient in roughly the same way: one blood draw and one collection, while the analyses are separated in the laboratory and the patient receives two results.
The multicancer test is currently available as a laboratory-developed test, giving the company room to continue research and collect evidence from real-world use. Shield has Breakthrough Device designation from the FDA in this area, but Guardant has not yet submitted a final approval application for the multicancer test. The company says its goal is to build a protocol and an organized study in preparation for a potential submission to the FDA, while also using the data in scientific publications, reimbursement strategy and algorithm improvement.
Why Does This Path Matter?
Shield’s experience shows that the ease of collecting a blood sample may help reach people who do not accept traditional screening options, but clinical value does not depend solely on detecting a cancer signal. A positive result requires colonoscopy for confirmation and treatment, while the test’s ability to detect early stages and precancerous lesions remains a critical factor in evaluating its usefulness.
Blood tests are gaining additional momentum in the United States after the American Cancer Society endorsed their use this year for people unwilling to undergo stool testing or visual examination, and after UnitedHealthcare, the largest private health insurer in the United States, agreed to cover Shield for its members. Nevertheless, expanded coverage alone does not resolve questions about accuracy, follow-up and approval; Guardant needs to demonstrate that increased screening uptake is accompanied by completion of subsequent procedures and improved ability to detect cancer at its earliest stages.