FDA Approves Guardant Health’s Shield Blood Test for Colorectal Cancer Screening

Introduction

On Monday, the U.S. Food and Drug Administration (FDA) granted approval to Guardant Health’s Shield blood test for colorectal cancer screening, representing a pivotal advancement in early cancer detection. Although Shield is not designed to replace traditional colonoscopies, its endorsement has sparked significant enthusiasm among medical professionals. They view it as a potential transformative tool for addressing the historically low screening rates for colorectal cancer, the second-leading cause of cancer mortality in the United States.

Details of the Shield Blood Test

Previously available to patients as an out-of-pocket screening option costing $895, the FDA approval is anticipated to broaden access through Medicare and private insurance coverage. This expansion is expected to enhance patient access and potentially elevate screening rates.

Dr. Arvind Dasari, an associate professor at the Department of Gastrointestinal and Medical Oncology at the University of Texas MD Anderson Cancer Center, welcomed the FDA approval, characterizing it as a “positive development.” Nevertheless, he cautioned that the true impact of Shield on screening rates and mortality reduction will become evident only over time.

The American Cancer Society projects that over 53,000 individuals will succumb to colorectal cancer this year. The Shield test, which analyzes blood samples to detect DNA fragments shed by cancerous tumors, has demonstrated an 83% effectiveness rate in identifying colorectal cancers, according to research published in March. However, the test is notably more effective at detecting advanced-stage cancers, where tumors release larger quantities of detectable DNA. The study indicated that Shield identified only 13% of earlier-stage polyps, highlighting its limitations in early-stage detection.

Screening Recommendations and Follow-Up

For optimal efficacy, Shield should be administered every three years beginning at age 45, in line with current colorectal cancer screening guidelines. It is crucial to note that a positive result from Shield does not provide a definitive diagnosis of cancer. A follow-up colonoscopy is required to confirm the presence of cancer, assess the location and extent of tumors, or determine if the initial results were false positives.

Robert Smith, Senior Vice President of Early Cancer Detection Science at the American Cancer Society, emphasized the necessity of a follow-up colonoscopy following a positive Shield test result. “It’s essential to understand that a positive Shield test requires a colonoscopy to confirm the presence of an advanced lesion or colorectal cancer, or to verify whether the results were false,” Smith explained. “A positive test is incomplete without a colonoscopy.”

Comparison with Other Screening Methods

The Shield blood test is the second blood-based screening option for colorectal cancer, following the approval of Epigenomics’ Epi proColon in 2016. However, Epi proColon has seen limited uptake due to concerns over its accuracy and its lack of coverage by Medicare and private insurers.

In contrast, Shield’s approval could address some barriers to colorectal cancer screening. Since the mid-1990s, there has been a troubling increase in colorectal cancer rates among individuals under 55, with an annual rise of 1% to 2% in this age group. Conversely, rates and mortality among individuals aged 60 and older have been declining, according to the American Cancer Society.

Dr. William Grady, a gastroenterologist at Fred Hutchinson Cancer Center in Seattle, emphasized the preventability of colorectal cancer through screening. “It’s disheartening because colorectal cancer is preventable,” Grady remarked. “One of my greatest satisfactions is removing polyps during colonoscopy that, if left untreated, would have progressed to cancer.”

Barriers to Screening and Patient Perspectives

Despite the proven efficacy of colonoscopy in detecting colorectal cancer, screening rates remain troublingly low, with fewer than 60% of eligible individuals adhering to recommended screenings. Dr. Sapna Syngal, Director of Strategic Planning for Prevention and Early Cancer Detection at the Dana-Farber Cancer Center in Boston, underscored the importance of increasing screening rates. “If this test boosts the number of people getting screened, it will have a substantial impact.”

Dr. Grady noted that adults in their 40s and 50s, who are often balancing work and family responsibilities, tend to be the least compliant with screening recommendations. The inconvenience and discomfort associated with colonoscopy preparation, which involves a day of bowel cleansing and the procedure itself, contribute to low participation rates.

Electra Paskett, Deputy Director for Population Sciences and Community Outreach at the Ohio State University Comprehensive Cancer Center, acknowledged the challenges associated with colonoscopy preparation. “Many people find the stool handling and the colonoscopy prep unpleasant,” Paskett said. “A blood test would be ideal for many individuals.”

Other screening methods include fecal occult blood tests, which detect blood in the stool as a potential indicator of colon polyps or cancer. The FIT-DNA tests, such as Cologuard, are effective at detecting cancer but less proficient at identifying precancerous polyps.

Patient Experience and Impact

John Gormly, a 77-year-old resident of Newport Beach, California, illustrates the potential impact of the Shield test. After avoiding colonoscopy screenings for years, Gormly opted for the Shield blood test upon his doctor’s recommendation. “My doctor called me a day or so later and said, ‘I’m not happy with the results. I’m going to send you for a colonoscopy,’” Gormly recounted. The subsequent colonoscopy revealed stage 2 colon cancer, which was successfully treated by surgeons. “I’m grateful I took that blood test,” Gormly said. “I never felt anything and had no symptoms. Without that blood test, I’m unsure how it would have turned out.”

Conclusion

The FDA’s approval of Guardant Health’s Shield blood test marks a significant milestone in colorectal cancer screening. By potentially improving accessibility and encouraging increased screening, Shield could play a vital role in enhancing early detection rates and reducing mortality associated with colorectal cancer. As the medical community and patients navigate the implications of this new screening tool, it is clear that while Shield offers a promising option, it should be used in conjunction with comprehensive diagnostic follow-up rather than as a replacement for colonoscopy.