Introduction
What is a liquid biopsy, what are its uses, and how could it be used in MCED testing?
A liquid biopsy (LB) is a fluid-based biomarker test to aid in disease detection. Different types of LBs detect different biomarkers, including:
- Circulating cell-free DNA (cfDNA) – fragments of DNA that are routinely shed into the blood by all cells in the body
- Circulating tumor DNA (ctDNA) – cfDNA that is shed specifically by tumor cells
- Exosomes – tiny, extracellular vesicles that contain genetic material and other molecules
- Circulating tumor cells (CTCs) – intact, whole tumor cells that are shed into the blood by the larger tumor mass
One advantage of CTC analysis is that it allows for complete assessment of both tumor DNA and tumor RNA, enabling analysis of the transcriptome, which is translated into the final protein product of a cell. Interestingly, CTCs were observed in a patient with metastasis as early as 1869,1 but the FDA only approved the first liquid biopsy CTC test in 2004.2
Several clinical applications of LB testing exist. Non-cancer clinical applications include use in organ transplant monitoring to detect graft dysfunction, as cell counts in the blood can increase during organ rejection. LBs also can be used for organ damage assessment after myocardial infarction or in autoimmune disease monitoring. Non-invasive prenatal testing (NIPT), which measures fetal circulating free DNA in the mother’s blood, has been used globally for the screening of fetal chromosomal aneuploidies (such as Down syndrome or trisomy 13 or 18) and has led to a 40% reduction in invasive prenatal testing procedures. LBs can also diagnose infectious diseases and help manage conditions like sepsis and tuberculosis.
Clinical application of LBs in the cancer space can be grouped into four categories:
- Optimal treatment selection and real-time monitoring of response to treatment (prognosis)
- Detection of recurrence after a period of remission or minimal residual disease detection
- Identification of treatment-resistance mechanisms that, once identified, may require a change in treatment strategy or even lead to the development of new target therapy drugs
- Screening and early detection for cancers, including MCED testing
The use of MCED tests for cancer screening and detection is a rapidly developing field attracting significant interest and investment from government health agencies and insurance companies. While some liquid biopsies screen for a single cancer, MCED tests can detect biomarker signals from multiple cancers (up to 50 or more cancers) with a single blood draw.
Experience with MCED tests to date
The current recommendation for MCED tests is to conduct them in conjunction with, rather than instead of, currently recommended screening tests. Primary advantages of MCED tests include the following:
- Blood samples are generally easily obtainable and the sampling procedures are minimally invasive and quick and incur less pain and risk.
- The technology not only detects signals of possible cancer in the first instance in a non-invasive way, but also could determine the likely cancer site or tissue of origin (TOO).
CancerSEEK, which detects eight common cancers, was the focus of one of the early trials published in the MCED space. The test demonstrated reasonable sensitivity (ability to identify an individual who has cancer) and specificity (ability to designate an individual who does not have cancer), and accuracy for TOO detection was 63%. A follow-on feasibility and safety study of 10,000 women without cancer, in which positive test results were followed up with PET CT scans, showed 65% of detected cancers were at a localized or regional stage. The study reported no change in screening behavior and minimal unnecessary invasive diagnostic procedures performed due to false positive tests. The study concluded that CancerSEEK may be a feasible and safe test to complement standard-of-care screening.3
The three-part Circulating Cell-free Genome Atlas (CCGA) study trialed GRAIL’s MCED test, Galleri. DNA methylation, the specific method of detection used by the Galleri test, enhanced tissue of origin (TOO) detection, resulting in an 88.7% TOO in true positives in the third validation CCGA study. Overall specificity of the Galleri test was 99.5%. While good, that amounts to 1 in 200 false positive test results. Overall sensitivity was 51.5%, meaning that approximately half of all cancers were detected. Having high sensitivity is important to ensure the test can detect low-volume, smaller tumors, but sensitivity was lower at earlier stages – 16.8% at stage 1, 40.4% at stage 2 – and higher at later stages – 77.0% and 90.1% for stages 3 and 4, respectively. Sensitivity also varied by cancer type, proving sub-optimal for breast cancer at 30.5%, but better for lung at 74.8%, colorectal at 82%, pancreatic at 83.7%, and ovarian cancer at 83.1%. This is significant as some in the latter group have no current screening modality, are more aggressive, are often detected late in the clinical course, and contribute significantly to current cancer mortality. Also of note, the Galleri MCED test detected cancer signals in more than 50 cancer types. 4,5,6
PATHFINDER is the most recent Galleri trial result to be released. This prospective study of a screening population evaluates the clinical feasibility, or implementation of the test following a cancer signal-detected result, in those ≥50 years of age with and without risks over a 12-month follow-up period. The primary outcome identified length and extent of diagnostic testing required to confirm the presence or absence of cancer. Of the 6,621 adults over 50 with analyzable results and without symptoms suggestive of cancer, a cancer signal was detected in 92 of them (1.4%), of whom a cancer diagnosis was subsequently confirmed in 35 people (38%) – the true positives. The remaining 57 (62%) had no cancer diagnosis – the false positives. Median time required for diagnostic resolution was shorter in the true positives, and fewer procedures were performed on this group than on those with false positive results. Specificity of the test was 99.1%; standard screening in the study population identified 29 cancers. Further clinical utility studies to expand on these findings likely will follow.7
Opportunity for early detection
Traditional screening methods used today are already quite effective at diagnosing targeted cancers at earlier stages and have led to strong improvements in cancer mortality outcomes. However, the cancers primarily screened for today in the U.S. (breast, colorectal, prostate, and cervical cancer) make up less than a quarter of cancer deaths.8 Screening of lung cancer is available but is limited and highly targeted with low take-up rates. The greatest potential for cancer mortality improvements lies in detecting cancers that currently go unscreened and are diagnosed at later stages and with poor prognosis. These include cancers such as lung, pancreatic, liver, esophagus, and stomach, which together made up about 20% of new cancer diagnoses in the U.S. in 2023 but almost 40% of all cancer deaths.9 The five-year relative survival rate,10 across all stages and by stage at diagnosis, for this group of cancers is, as expected, quite poor at around 24% but varies by cancer.
Figure 1: Five-year survival rates for cancers commonly diagnosed at later stages (U.S.)
Figure 2: Stage mix at diagnosis for cancers commonly diagnosed at later stages: 2011-2020 (U.S.)11
To estimate the potential for mortality improvements resulting from a “left shift” in the stage mix at which these cancers are diagnosed, consider a scenario in which MCED testing is used to detect some cancers at earlier stages. For example, the mix at the local and regional stages might move 5% higher, with a corresponding decrease at the distant stage, such as going from a 40/30/30 local/regional/distant split to 45/35/20.
Figure 3: MCED testing scenario: projected shift in five-year survival rates
This scenario projects an improvement of approximately 15% in the five-year survival rate and a 5% reduction in the overall cancer mortality rate.
Key assumptions to consider in modeling the impact of MCED tests
Actuaries need to consider the impact of emerging medical technology on future mortality and morbidity rates, particularly with insurance products that provide long-term guarantees. Models can test for a range of potential results, which is particularly important with some key assumptions having a large degree of uncertainty around them and with much yet to be learned regarding the real-world implementation of these tests.
Important assumptions to consider include the following:
- Effectiveness. What is the probability that an LB can detect a cancer where one exists? This is represented by the sensitivity of the test and, as we have seen, varies significantly by stage of cancer and site.
- Uptake. How widely will the tests be used in different age groups as part of population screening programs, what screening interval will be recommended, and what proportion of the population will elect to screen themselves regularly?
- Acceleration. How much earlier will cancers be diagnosed by MCED tests relative to when they are diagnosed today by either traditional screening programs or via tissue biopsies and clinical investigations following symptoms?
Actuaries need to explore data and information available for each of these assumptions to develop an estimate and define potential sources of uncertainty in these estimates.
Effectiveness
Out of the three key assumptions, effectiveness has the most information available. Several studies have estimated the accuracy of MCED tests for TOO and at different stages.12 These studies have found that the tests are generally effective, although it varies by cancer, and, importantly, that the tests are more effective at later stages. Any model therefore needs to allow for different effectiveness assumptions by site and stage of cancer.
The effectiveness of MCED tests likely also will improve in the future as additional data obtained through further clinical studies improves the tests’ ability to detect more cancers earlier. Future estimates of this assumption are uncertain and should be sensitivity-tested, as part of optimistic and pessimistic scenario modeling, for example.
Uptake
It is uncertain if, when, and how quickly MCED tests will be adopted as part of large-scale population screening programs. That likely also will vary by geography. Clinical trials are now underway to gather more data and evaluate the effectiveness and feasibility of the tests. It is reasonable to expect the uptake of MCED tests will grow slowly over time, depending on several factors. Modelled assumptions therefore should vary by calendar year and consider the following:
- Scalability of the technology
- Costs, and whether economies of scale bring down the cost of these tests, particularly when provided as part of government-sponsored healthcare screening
- Regulatory approvals and government health departments’ inclusion of MCED tests as part of recommended screening programs
- Behavioral factors such as consumer comfort with the tests relative to current screening tests and data and privacy concerns around the use of genetic material
In setting the uptake assumption, current screening rates can serve as a guide; however, considerable subjectivity remains, depending on views of relevant factors and the scenario being considered. As such, current screening rates can help set the long-term uptake assumption in one of two ways:
- As a floor in an optimistic scenario – the tests are cost effective, rolling out the tests at scale is successful, and the less invasive nature of the tests drives uptake
- As a ceiling in a more conservative scenario – uptake is strong but not expected to surpass current screening uptake due to behavioral factors, costs, and healthcare capacity
Another consideration is how the uptake will vary by age. Again, current screening rates can be used as a guide to gauge which age groups likely will be targeted with MCED test screening programs.
Sensitivity testing using a variety of scenarios is crucial given the current uncertainty about how the rollout of MCED tests will occur.
Acceleration
Acceleration assumptions capture expectations around how much earlier LBs will diagnose cancers compared to traditional screening or investigation of patient symptoms. Acceleration presents two impacts to consider in a model:
- Cancers diagnosed earlier can be treated earlier and thus likely would respond better to treatment, improving mortality outcomes.
- Diagnosing cancer at an earlier stage increases survival rates, given current mortality outcomes by stage.
The mortality improvements attributable to each of these are difficult to determine. One approach is to determine the number of years of acceleration expected, which likely varies by cancer:
- Currently screened cancers already are diagnosed quite early, given the success of traditional screening programs, resulting in limited acceleration potential from the introduction of LB tests for these cancers, compared to the greater opportunity for acceleration among unscreened cancers.
- More aggressive cancers that, on average, progress more quickly have a shorter window for acceleration, relative to cancers that on average progress more slowly.
By expressing acceleration periods in years, it is possible to compare against typical progression times between stages to estimate the probability of accelerating diagnosis to an earlier stage. If the acceleration period in years is higher than the progression time between stages, then accelerating to an earlier stage is more likely.
The acceleration period also can inform assumptions around the mortality improvements from earlier diagnosis without acceleration to an earlier stage, for instance via an assumption that allows for cancer mortality reduction proportional to the number of years of acceleration. The subjectivity and uncertainty in setting this assumption can be mitigated by leveraging medical expertise and employing sensitivity testing.
A new model for assessing the impact on future mortality and morbidity
˿ƵAPP has built a model to assess the impact of MCED tests on cancer morbidity and mortality in future calendar years.
Morbidity impact
In modeling the impact on cancer morbidity rates, our approach was to shift a portion of incidence from older ages to younger ages, where the proportion of incidence accelerated depends on the assumptions discussed above and include:
- The uptake or percentage of people at a given age screened via MCED tests
- The effectiveness and probability that the MCED test detects a cancer, which varies by site and stage at diagnosis
- The acceleration period, or the number of years that the diagnosis is accelerated, which determines the new age at which the incidence occurs
As these assumptions change over time, the proportion accelerated relative to current incidence rates would change.
It is also important to consider the overdiagnosis of cancer, a common feature of all early cancer screening programs. This represents cancer incidence that would not have been diagnosed previously, as the cancer was asymptomatic, was slow to progress, and had no impact on mortality of the life. As MCED tests are rolled out, more of these incidental cancers will be detected and could be eligible for living benefits claims under a critical illness policy. An increase in incidence rates therefore should proportionally reflect the rate of overdiagnosis expected by cancer site and the uptake and effectiveness of LBs. With the effectiveness of LBs currently lower for early-stage cancers, the amount of cancer overdiagnosis should be limited initially.
The probability of acceleration to earlier stages also should be considered, given its impact on cancer mortality rates. This is also important if modeling impacts on staged cancer products, where cancers diagnosed at earlier stages may be eligible for only partial benefits. This expected acceleration in the stage mix and lower benefit payment could offset claim acceleration to younger ages for staged cancer products.