Trending Clinical Topic: Cancer Blood Test

Ryan Syrek


August 19, 2022

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Long after the rise and fall of Theranos, the potential of powerful diagnostic information obtained from a single blood draw has once again captured much attention. The Galleri blood test can detect as many as 50 different types of cancer and is now being offered in various settings (see Infographic below). Although some experts are enthusiastically calling it a game-changer, some questions have arisen about its use. Having a blood test for multiple cancers is a "very good idea and the scientific basis for this platform is sound," said Timothy R. Rebbeck, PhD. "But the devil is in the details to ensure the test can accurately detect very early cancers and there is a pathway for subsequent workup (diagnosis, monitoring, treatment, etc)."

The test uses cell-free DNA (cfDNA) sequencing and has an overall sensitivity for any stage of cancer of 51.5%. Sensitivity was better for later-stage cancers (77% for stage III and 90.1% for stage IV) and lower for early-stage cancers (16.8% for stage I and 40.4% for stage II). Galleri is offering the test to patients older than 50 years who have a family history of cancer, as well as those who are high risk for cancer or immunocompromised. A prescription is required, and patients must pay for it out of pocket (around $950). It is not covered by medical insurance and is not approved by the US Food and Drug Administration.

A different kind of diagnostic blood test, one that uses nuclear magnetic resonance (NMR) metabolomics, was recently established as the first to determine the metastatic status of a cancer without prior knowledge of the primary cancer type. Researchers analyzed blood samples from 300 patients with nonspecific but concerning symptoms of cancer. Unlike conventional blood-based cancer tests, the NMR-based technique analyzes metabolite levels as biomarkers to distinguish between different cancer states. In the study, NMR-based metabolomic analysis correctly detected the presence of solid tumors in 19 out of 20 patients with cancer and identified metastatic disease with an accuracy of 94%.

Another blood test that analyzes circulating tumor DNA (ctDNA) shed by metastatic cancers may allow for personalized treatment plans. Wyatt and colleagues analyzed serial plasma and synchronous metastases in patients with aggressive, treatment-resistant prostate cancer using deep whole-genome sequencing. They then used newly developed computer programs to provide information about the genetic makeup of each cancer population. This allows researchers to learn about a patient's overall disease rather as opposed to just one metastatic tumor. In the future, this may allow clinicians to make better decisions about managing a patient's cancer.

ctDNA is also at the center of a new blood assay designed to screen for colorectal cancer (CRC). The first prospective study to evaluate the test found that at 90% specificity, the blood assay (Guardant Health) was 100% sensitive for detecting CRC. At 95% specificity, sensitivity was 88%. The study was presented May 21 at Digestive Disease Week (DDW) 2022, held virtually and in San Diego, California. One third of participants (33%) were at average risk. Of the remainder, 49% were symptomatic, 11% had a positive family history of CRC, 6% had a positive stool-based test result, and 1% presented for colonoscopy for other reasons. The study included people aged 45-84 years (median age, 55 years). Just over half (52%) were women. The prevalence rate of colorectal adenocarcinoma was 2.6%. Eight patients had stage I cancer, three had stage II cancer, two had stage III cancer, and two had stage IV cancer.

Another simple blood test that looks for a combination of specific RNA snippets is also being explored as a CRC screening tool. In a new study, researchers identified four microRNAs that together comprise a signature biomarker that can be used to detect and diagnose CRC from a liquid biopsy in a younger population. In a Japanese cohort, the four-microRNA assay had a sensitivity of 90% and a specificity of 80%, with a positive predictive value (PPV) of 88% and a negative predictive value (NPV) of 84%. In a Spanish cohort used for validation, the assay had a sensitivity of 82%, a specificity of 86%, a PPV of 88%, and an NPV of 80%. By disease stage, the four-microRNA panel identified both early-stage (stage 1-2, sensitivity 92%, specificity 80%) and late-stage (stage 3-4, sensitivity 79%, specificity 86%) early-onset CRC in the validation cohort.

The recent rise in cancer-detecting blood tests has generated a great deal of attention. From tests that can broadly suggest the presence of various oncologic concerns to others more specific to CRC, the potential of a simple blood draw to indicate the presence of cancer is widely appealing, even if the next steps are still being worked out. That wide appeal led to this week's top trending clinical topic.

Learn more about CRC screening.


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