Multi-cancer early detection liquid biopsy testing: A predictive genetic test not quite ready for prime time

The process to develop and validate GRAIL’s blood-based cancer screening test includes 4 large clinical trials of more than 180,000 participants, including those with cancer and those without. The Circulating Cell-Free Genome Atlas (CCGA) Study, was a prospective, case-controlled, observational study enrolling approximately 15,000 participants with 3 prespecified sub-studies. The first sub-study developed the machine-learning classifier for both early detection and tumor of origin detection.^25,26

The highest performing assay from the first sub-study then went on to be further validated in the 2nd and 3rd sub-studies. The 3rd sub-study, published in the Annals of Oncology in 2021 looked at a cohort of 4,077 participants with and without cancer, and found the specificity of cancer signal detection to be 99.5% and the overall sensitivity to be 51.5%, with increasing sensitivity by cancer stage (stage I - 17%, stage II - 40%, stage III - 77%, and stage IV - 90.1%).²⁴ The false-positive rate was low, at 0.7%, and the true positive rate was 88.7%. Notably, the test was able to correctly identify the tumor of origin for 93% of samples.²⁴ The study overall demonstrated high specificity and accuracy of tumor site of origin and supported the use of this blood-based MCED assay.

The PATHFINDER study was another prospective, multicenter clinical trial that enrolled more than 6,000 participants in the United States. The participants were aged >50 years with or without additional cancer risk factors. The goal of this study was to determine the extent of testing required to achieve diagnosis after a “cancer signal detected” result. The study results found that, when MCED testing was added to the standard-of-care screening, the number of cancers detected doubled when compared with standard cancer screening alone.^27,28 Of the 92 participants with positive cancer signals, 35 were diagnosed with cancer, and 71% of these cancer types did not have standard-ofcare screening. The tumor site of origin was correctly detected in 97% of cases, and there were less than 1% of false positives. Overall, the test led to diagnostic evaluation of 1.4% of patients and a cancer diagnosis in 0.5%.

Currently, there are 2 ongoing clinical trials to further evaluate the Galleri MCED test. The STRIVE trial that aims to prospectively validate the MCED test in a population of nearly 100,000 women undergoing mammography,²⁹ and the SUMMIT trial,³⁰ which is similarly aiming to validate the test in a group of individuals, half of whom have a significantly elevated risk of lung cancer.

With the promising results described above, the Galleri test became the first MCED test available for commercial use starting in 2022. It is only available for use in people who are aged 50 and older, have a family history of cancer, or are at an increased risk for cancer (although GRAIL does not elaborate on what constitutes increased risk). However, the Galleri test is only available through prescription—therefore, if interested, patients must ask their health care provider to register with GRAIL and order the test (https://www .galleri.com/hcp/the-galleri-test/ordering). Additionally, the test will cost the patient $949 and is not yet covered by insurances. Currently, several large health care groups such as the United States Department of Veterans Affairs, Cleveland Clinic, and Mercy hospitals have partnered with GRAIL to offer their test to certain patients for use as part of clinical trials. Currently, no MCED test, including the Galleri, is approved by the US Food and Drug Administration.

Incorporating MCED testing into clinical practice

The Galleri MCED test has promising potential to make multi-cancer screening feasible and obtainable, which could ultimately reduce late-stage cancer diagnosis and decrease mortality from all cancers. The compelling data from large cohorts and numerous clinical trials demonstrate its accuracy, reliability, reproducibility, and specificity. It can detect up to 50 different types of cancers, including cancers that affect our gynecologic patients, including breast, cervical, ovarian, and uterine. Additionally, its novel methylation-based assay accurately identifies the tumor site of origin in 97% of cases.²⁸ Ongoing and future clinical trials will continue to validate and refine these methods and improve the sensitivity and positive-predictive value of this assay. As mentioned, although it has been incorporated into various large health care systems, it is not FDA approved and has not been validated in the general population. Additionally, it should not be used as a replacement for recommended screening.

CASE Resolved

The patient is eligible for the Galleri MCED test if ordered by her physician. However, she will need to pay for the test out-of-pocket. Due to her family history, she should consider germline genetic testing (either for herself, or if possible, for her father, who should meet criteria based on his prostate cancer).³ Panel testing for germline mutations has become much more accessible, and until MCED testing is ready for prime time, it remains one of the best ways to predict and prevent cancers. Additionally, she should continue to undergo routine screening for cervical, breast, and colon cancer as indicated. ●