Non-invasive, blood-based liquid biopsy tests have long been touted as the future for cancer diagnostics, but studies presented at the recent European Society for Medical Oncology (ESMO ) Congress 2022, highlight the challenges remaining before they can reach routine clinical practice.
In results from Grail’s PATHFINDER study which evaluated its multi-cancer early detection blood test in a screening population of 6,632 individuals aged 50 years or older, there was a low positive predictive value of 43.1% for the detection of early-stage cancer but a high negative predictive value, of 98.5%. Among those with a positive test result, the time till they received a diagnostic resolution was a median of 79 days. Among participants with a positive screening test, diagnostic resolution was achieved within three months for 73%.
One of the difficulties for these blood-based tests, according to Dr Umberto Malapelle from the Department of Public Health at the University of Naples II, Italy is the low and variable number of biomarkers in early-stage cancers. This means that different blood samples from the same individual can yield different results and the liquid biopsy techniques need to be highly sensitive. However, a high sensitivity also poses a challenge as it can impact the specificity of the test, with benign mutations triggering false-positive results.
The progress across blood-based cancer diagnostics will rely on researchers understanding a patient’s individual risk, as well as implementing a range of testing methods such as sensors, contrast agents, molecular methods, and artificial intelligence to help detect cancer-specific signals in real time.
“One of the problems from a biological perspective is a low quantity of bioanalytes, so the assays are not yet ready for use in clinical practice. At an early stage, in fact, the quantity of ctDNA is not high and a combined assessment of different biological aspects may be needed to improve sensitivity, for example point mutation insertion and selection or DNA methylation,” explains Malapelle.
Research presented at ESMO highlighted the potential of infrared molecular fingerprinting (IMF) of liquid and plasma as a complementary analytical tool for cancer screening. In one large, multi-center, multi-cancer study, infrared molecular fingerprints of plasma and serum were assessed in patients with different solid cancer tumours.
Focusing on breast, bladder, prostate, and lung cancer, IMF was found to detect cancer through a machine algorithm that obtains binary classification performance in the range of 0.78–0.89 (area under the receiver operating characteristic curve, with a clear correlation between AUC and tumour load.) The spectral signatures were found to differ between different cancer types, allowing the distinction between different cancers in a single measurement.
The study suggests that blood-based IMF patterns can help identify various cancer entities and provides a potential future in vitro diagnostic tool to accompany liquid biopsy. “We need this type of study to combine different types of methodologies that analyse the biological and physical aspects of tumours,” says Malapelle. “This allows the possibility to improve the sensitivity and specificity of [liquid biopsy] assays and the detection rate for different tumours. This is useful for the metastatic setting and to detect cancers in the early stages of disease.”
According to Fabrice André, Director of Research at Gustave Roussy Cancer Centre at Villejuif, France, in the next five years, more doctors, surgeons, nurses as well as diagnostic and treatment infrastructure will be needed to care for the rising number of people who will be identified by multi-cancer early detection tests. “We need to involve all stakeholders in deciding new pathways of care. We need to agree who will be tested and when and where tests will be carried out, and to anticipate the changes that will happen as a result of these tests, for example in the diagnosis and treatment of people with pancreatic and other cancers that are usually diagnosed at a much later stage,” he announced.
The accessibility to testing is also expected to vary and may potentially widen health inequity between countries. “From a clinical point of view, we know we can improve on the proportions of patients who can undergo multi-cancer testing, but first we need to identify laboratories that are able to perform these types of tests and overcome economic barriers, especially in developing countries,” says Malapelle.
The impact of early screening tests on patient wellbeing is another consideration. Analysis from Grail’s PATHFINDER study explored the potential for early cancer detection testing to cause anxiety and distress in individuals with a positive test result. The reliability of the tests is particularly pertinent if they are used to detect cancer in patients with no clinical symptoms and who are unaware of the risk of a potential diagnosis.
Overall, based on the research, considerable progress is being made in early cancer diagnostics, but additional studies are needed to fully understand how these technologies will be implemented to maximize clinical benefit.