A blood-based platelet RNA test that uses the equivalent of one drop of blood can identify patients with cancer, differentiate between cancer types, and even pick out mutant biomarkers, say European researchers.
In a study published online November 9 in Cancer Cell, the team reports that RNA from "tumor-educated" platelets containing tumor-associated biomolecules could distinguish cancer patients from healthy individuals with an accuracy of 96%.
Furthermore, the test, which may eventually help in cancer diagnosis and guide treatment selection, could differentiate six primary tumor types with an accuracy of 71%, as well as identify specific breast and lung cancer mutant biomarkers.
Coauthor R Jonas A Nilsson, PhD, department of radiation sciences, oncology, Umea University, Sweden, told Medscape Medical News: "Earlier and better diagnosis is a crucial element in curing patients or turning the disease into a manageable, more chronic disease."
"Our technology has the potential to contribute to that goal. It is our objective to show that we can deliver tests that allow costs to be saved at other points in the healthcare system."
The test complements other liquid biopsy tests that detect portions of tumor cell somatic mutant DNA shed into the circulation or released when tumor cells die, which as reportedby Medscape Medical News, could allow tumors to be detected, measured, and tracked.
Indeed, two studies in a range of cancer types showed that circulating (ct)DNA tests can identify tumors at a very early stage, monitor tumors for metastasis, and even pinpoint treatment resistance. However, these applications are not ready for transfer to the clinic, although these applications are not ready for transfer to the clinic.
There are crucial differences between the ctDNA tests and the current mRNA test, however. Terence Friedlander, MD, from the Helen Diller Family Comprehensive Cancer Center at the University of California, San Francisco, who did not participate in the study, noted: "Current ctDNA tests generally focus on profiling a predefined panel of genes, and report whether or not a mutation is detected."
"These ctDNA tests therefore do not distinguish between different tumor types; rather, they provide additional insight into possible mutations within a known tumor. Because not all tumors will have detectable mutations, current ctDNA tests are not designed to screen patients for occult cancer, and may not be reliable in detecting recurrence of cancer after definitive treatment," he pointed out.
He told Medscape Medical News: "In contrast, the platelet mRNA methodology described here may be more multifunctional, in that it can distinguish between a cancer patient and a healthy donor, may be able to detect the type of cancer present and, if validated in future studies, detect recurrent cancers."
Study DetailsFor their study, Dr Jonas and colleagues isolated blood platelets from 55 healthy donors aged 21 to 64 years, as well as treated and untreated patients with early, localized cancer (n = 39) and advanced, metastatic cancer (n = 189).
The cancer patients included 60 with nonsmall cell lung carcinoma, 41 with colorectal cancer, 39 with glioblastoma, 35 with pancreatic cancer, 14 with hepatobiliary cancer, and 39 with breast cancer.
The team purified 100 to 500 pg of platelet total RNA, the equivalent of less than one drop of blood, for SMARTer mRNA amplification and sequencing.
From that, they identified 5003 different protein coding and noncoding RNAs for subsequent analysis, of which 1453 were increased and 793 decreased in tumor-educated platelets versus samples from healthy donors.
Using a training cohort of 175 patients and an algorithm previously developed to classify primary and metastatic tissues, the team found on ANOVA testing that a panel of 1072 platelet RNAs could identify cancer with a sensitivity of 96%, a specificity of 92%, and an accuracy of 95%.
Clustering of platelet mRNA levels between healthy donors and individual cancer types resulted in a series of tumor-specific gene lists. Using a combination of algorithms based on these lists, the team was able to differentiate between tumor types with an average accuracy of 71% (P < .01).
Finally, researchers examined the ability of platelet RNA profiling to identify specific mutant biomarkers. Although biomarker levels were often low or undetectable, they were able to develop biomarker-specific gene lists for the algorithms.
These were able to distinguish patients with HER2-amplified, PIK3CA mutant and triple-negative breast cancer, and nonsmall cell lung carcinoma patients with MET overexpression (P < .01).
Could Guide Treatment Decisions
Dr Nilsson believes that the test, if proven in further studies, could be used in a number of different ways. He said, "The amount of information we get from the platelet-derived RNA profiles enable the technology to be applied in different diagnostic settings."
"We show it can be powerful in screening applications, but also in guiding primary diagnosis, driving treatment decisions, and longitudinal treatment monitoring," he said.
As the test is also able to distinguish between mutant biomarkers, it could also play an important role in the delivery of personalized cancer care. Dr Nilsson said, "When it comes to personalized cancer care, we may offer an all-in-one solution, from the first time the patient comes in contact with the healthcare system by participating in a screening program ... to making therapeutic stratification based on genetic alterations within the tumor."
Nevertheless, Dr Nilsson and colleagues continue to work on improving the test. He noted that it is "already highly accurate," but added, “we continue to increase the numbers of samples to make the test more robust and accurate.”
"The workflow of the test method is now well-established and further validation, as well as expansion of the repertoire of cancer types, are important next steps."
To those ends, the team are working with numerous groups and setting up studies to validate the findings in the clinical setting, as well as to take into account systemic factors that may affect the platelet mRNA profile, which the authors note may include inflammatory diseases or cardiovascular events and other noncancerous diseases
As our technology is easily implemented in the clinical workflow (all labs know how to isolate platelets) and as the results of our work to date have been remarkable, we have been approached by many investigators to collaborate," Dr Nilsson said.
Commenting, Dr Friedlander said: "Overall, the authors convincingly show that platelet mRNA profiles from cancer patients are different from healthy donors, and detectable using the described methodology."
"They employ a test set and a validation cohort, and the results are comparable, giving confidence to their findings that the mRNA profiles differ between cancer patients and healthy donors," he explained.
However, he cautioned, the findings need to be replicated in further studies. "While the authors discuss using this to screen patients for cancer, this may require significant further validation, as this work was done in patients with a known malignancy," he said.
"It is not clear whether this methodology will have the same accuracy in patients with early, localized tumors, as opposed to those that have grown large enough to be detected by traditional means. Nonetheless, this is an exciting and potentially wide ranging application, if it can be validated in a larger screening study," he noted.
Dr Friedlander said he believes another clinically relevant use for the test is that of surveillance for patients who have been treated for a localized tumor and are at risk for recurrence.
"One could imagine that this test might provide an early indication that a cancer is recurring before it is apparent on a radiologic scan," he said.
Dr Friedlander continued: "Similarly, this could potentially be used to help a clinician decide whether to give adjuvant therapy after a definitive treatment for cancer."
"In this scenario, patients with 'cancer' mRNA platelet profiles could be given more (i.e., adjuvant) therapy after definitive cancer surgery or radiation, while those with 'healthy' mRNA profiles could potentially be observed and avoid unnecessary therapy," he explained. "Again, this would have to be validated in an appropriately designed study before it could be recommended clinically."
In addition, the test could be used to profile cancers of unknown origin or to discover mutations in tumors that might not be amenable to biopsy, such as those in the brain or pancreas.
"That said, the accuracy of this test in this paper is not 100%, so it is unclear if treating patients based on the molecular alterations discovered by this test would actually have clinical impact," Dr Friedlander concluded.
Financial support was provided by grants from the European Research Council, the Netherlands Organisation of Scientific Research, Dutch Cancer Society (Stichting STOPhersentumoren.nl), US National Cancer Institute, CFF Norrland, and Swedish Research Council. Several coauthors are employees of thromboDx.
Cancer Cell. 2015;38(5):666-676. Full text