50 years ago, doctors needed to see cancer to diagnose it - and by then, it was usually too late to do anything about it. Newer tests have made cancer detection easier and more precise, but preventable cases continue to slip through the cracks, often with fatal consequences. However, a new test has the potential to stop these types of missed diagnoses--it can detect cancer from a single drop of blood, and it may finally allow us to ensure patients receive care when they need it.
Blood platelets are a major component of blood, best known for their ability to stop bleeding by clotting injured blood vessels. However, blood platelets are far more versatile than previously understood. When cancer is formed in the human body, the tumors shed molecules such as proteins and RNA directly into the bloodstream. The blood platelets come in contact with these shed molecules and will absorb them. This results in an alteration of the blood platelets’ own RNA. Persons with cancer will therefore have blood platelets that contain information about the specific cancer present. These “educated” blood platelets are called tumor educated platelets, or TEPs. Recently, TEPs have been used to aid in the detection of specific cancers, and even to identify their locations.1
In a recent study, a group of scientists investigated how TEPs could be used to diagnose cancer. The scientists took blood platelets from healthy individuals and from those with either advanced or early stages of six different types of cancer and compared their blood platelet RNA. While doing so, the researchers found that those with cancer had different amounts of certain platelet RNA molecules. For example, the scientists discovered that the levels of dozens of specific non-protein coding RNAs were altered in patients who had TEPs. The further analysis of hundreds of different RNA levels, from the nearly 300 patients in the study, enabled the scientists to distinguish a cancer-associated RNA profile from a healthy one. Using these results, the team created an algorithm that could classify if someone did or did not have cancer with up to 96% accuracy.1
Not only could the TEPs distinguish between healthy individuals and those with a specific type of cancer, but they could also identify the location of the cancer. The patients in the study had one of six types of cancer: non-small-cell lung cancer, breast cancer, pancreatic cancer, colorectal cancer, glioblastoma, or hepatobiliary cancer. The scientists analyzed the specific TEPs associated with the specific types of cancer and created an algorithm to predict tumor locations. The TEP-trained algorithm correctly identified the location of these six types of cancer 71% of the time.1
The authors of the study noted that this is the first bloodborne factor that can diagnose cancer and pinpoint the location of primary tumors. It is possible that in the near future, TEP-based tests could lead to a new class of extremely accurate liquid biopsies. Nowadays, many cancer tests are costly, invasive, or painful. For example, lung cancer tests require an X-ray, sputum cytology examination, or tissue sample biopsy. X-rays and sputum cytology must be performed after symptoms present, and can often have misleading results. Biopsies are more accurate, but are also highly painful and relatively dangerous. TEP-based blood tests have the potential to both obviate the need for these techniques and provide more granular, clinically useful information. They can be performed before symptoms are shown, at low cost, and with minimal patient discomfort, making them an ideal choice to interdict a growing tumor early.
The information that TEPs have revealed has opened a gate to many potential breakthroughs in the detection of cancer. With high accuracy and an early detection time, cancer blood tests have the potential to save many lives in the future.
- Best, M. et al. Cancer Cell 2015 28, 676
- Marquedant, K. "Tumor RNA within Platelets May Help Diagnose and Classify Cancer, Identify Treatment Strategies." Massachusetts General Hospital.