This was the conclusion of recent data presented by Ora Karp Gordon, MD, MS, during a session at the American Association for Cancer Research annual meeting.
Christos Evangelou/MDedge News
Dr. Ora Karp Gordon
The MCED test, known as Galleri, was made clinically available in the United States in April 2021. Developed by GRAIL LLC, the test analyzes cell-free DNA in the blood using targeted methylation analysis and machine learning to detect the presence of a cancer signal and determine its organ of origin or cancer signal origin. The initial screening of over 53,000 individuals with the Galleri test detected a cancer signal in 1.1% of participants.
The new real-world analysis examines the outcomes of repeat MCED testing in 5,794 individuals.
The study looked at individuals who initially received a ‘no cancer signal detected’ result and then underwent a second Galleri test. Over 80% of participants received their follow-up test 10-18 months after the first, with a median interval between blood draws of 12.9 months.
“The repeat tests detect those cancer cases that have reached the detection threshold since their last MCED test, which should be less than one year of incidence,” Dr. Gordon, professor at Saint John’s Cancer Institute, Santa Monica, California, said in an interview. “We are just now starting to see results from patients who get their second and even third round of screening.”
“Galleri is recommended to be used annually in addition to USPSTF [US Preventive Services Task Force]–recommended cancer screening tests, like mammography and colonoscopy,” she said.
This recommendation is based on a modeling study suggesting that annual screening would improve stage shift, diagnostic yield, and potentially mortality when compared to biennial screening, although biennial screening was still favorable compared with no screening, she explained.
Early Real-World Evidence of Repeat Testing
Among the cohort of 5,794 individuals who received repeat testing, 26 received a positive cancer signal on their second test, yielding a cancer signal detection rate of 0.45% (95% CI: 0.31%-0.66%). The cancer signal detection rate was slightly higher in men. The rate was 0.50% (95% CI: 0.32%-0.81%; 17 of 3367) in men versus 0.37% (95% CI: 0.2%-0.7%; 9 of 2427) in women.
During her presentation, Dr. Gordon highlighted that the repeat testing signal detection rate was lower than the initial 0.95% rate (95% CI: 0.87-1.0; 510 of 53,744) seen in the previous larger cohort of patients who were retested at 1 year.
She acknowledged that the lower cancer signal detection rate of repeat testing may indicate some degree of ‘early adopter’ bias, where those who return for a second test are systematically different from the general screening population. This could suggest that broader population-level screening may yield different results, she continued.
Shift Toward Unscreened Cancers
The top cancer types identified in the second round of testing were lymphoid, head and neck, bladder/urothelial, colorectal, and anal cancers. Clinicians were able to confirm clinical outcomes in 12 of 26 cases, in which cancer signals were detected. Of those 12 cases, 8 individuals received a cancer diagnosis and 4 did not have cancer. The remaining 14 of 26 cases in which cancer signals were detected are still under investigation.
“We found a shift away from USPSTF screen-detected cancers, like breast, lung, and prostate, and relative increase in unscreened urinary, head and neck, and lymphoid cancers, with 75% of cancers being those without any screening guidelines,” Dr. Gordon said in an interview.
She added that patients who choose to retest may have different cancer rates for several reasons, including bias toward a population that is health conscious and adhered to all recommended cancer screening.
“So the shift toward unscreened cancers is not unexpected and highlights the value of Galleri,” she said, but also acknowledged that “continued monitoring is needed to see if this translates in a persistent finding over time and tests.”
Shift Toward Early-Stage Cancers
Staging information was available for five cases, and Dr. Gordon highlighted in her talk that four of these confirmed cancers were stage I, including cancers of the anus, head and neck, bladder, and lymphoma. The fifth confirmed cancer with staging information was stage IV ovarian cancer.
“It is still early, and the numbers are very small, but the detection of early-stage cancers with second annual testing is very encouraging as these are the cases where MCED testing could have the greatest impact in improving outcomes through earlier treatment,” Dr. Gordon told this publication.
During an interview after the talk, Kenneth L. Kehl, MD, MPH, echoed that data must be confirmed in larger cohorts.
“The shift toward earlier stage cancers that are less detectable by standard screening methods is an interesting result, but we need to be cautious since the numbers were relatively small, and we do not have data on cancers that were diagnosed among patients whose second MCED test was also negative,” said Dr. Kehl, a medical oncologist at Dana-Farber Cancer Institute, Boston.
MCED Results Could Help Direct Diagnostic Workup
The test’s ability to predict the organ of origin was highly accurate, correctly identifying the cancer type in all eight confirmed cases. Among the eight cases with a confirmed cancer diagnosis, the accuracy of the first prediction was 100%, and diagnoses included invasive cancers across multiple tissues and organs, including anus, colon, head and neck, urothelial tract, ovary, and the lymphatic system.
“The fact that the site of origin for 100% of confirmed cancers was accurately predicted with GRAIL’s CSO by Galleri test confirms the promise that this can guide workup when a cancer signal is detected,” Dr. Gordon noted in the interview.
Looking Ahead
Dr. Kehl, who was not involved in the MCED study, noted in an interview that “further data on test characteristics beyond positive predictive value, including the sensitivity, specificity, and negative predictive value, as well as demonstration of clinical benefit — ideally in a randomized trial — will likely be required for MCED testing to become a standard public health recommendation.”
He added that challenges associated with implementing annual screening with MCED tests include the risks of both false positives and false negatives as testing becomes more widely available.
“False positives cause anxiety and lead to additional testing that may carry its own risks, and we need to understand if potentially false negative tests will be associated with less uptake of established screening strategies,” Dr. Kehl said in an interview. However, he noted that serial testing could lead to more frequent diagnoses of early-stage cancers that may be less detectable by standard methods.
Dr. Gordon reported financial relationships with GRAIL LLC and Genetic Technologies Corporation. Dr. Kehl reported no relationships with entities whose primary business is producing, marketing, selling, reselling, or distributing healthcare products used by or on patients.
