In a new study published in the journal Nature Communications researchers say it might be possible to detect some types of cancers through blood tests, offering hope for reducing cancer mortality by early detection.
The study called the Taizhou Longitudinal Study (TZL) recruited 123,115 subjects aged between 25-90 years who provided their plasma samples that were stored from 2007-2014 and monitored for cancer occurrence.
Using PanSeer, a noninvasive blood test that is based on circulating tumor DNA methylation, researchers report that by the end of 2017, a total of 575 initially healthy samples who presented as asymptomatic were diagnosed with one of the five most common cancer types (stomach, esophagus, colorectum, lung or liver) within four years of blood draw.
In their study, PanSeer was able to detect five common types of cancers in 95 per cent of asymptomatic individuals who were later diagnosed with cancer, demonstrating that cancer can be detected by non-invasive methods upto four years before symptom onset.
So what can the test actually do?
The PanSeer test is most likely to identify cancer in those individuals that already have cancerous growths but are asymptomatic to other diagnostic tests and screening methods. It cannot predict a patient who will develop cancer at a later stage if that individual does not already have a cancerous growth.
The PanSeer test is also a first-line screening method, a patient who tests positive on it will have to subsequently undergo a reflex blood test or follow-up imaging so that their tissue of origin can be mapped, followed by a pathological examination to confirm the presence of cancer. Importantly, the test cannot detect the type of cancer.
What are the limitations of this study?
The researchers note that because modern plasma preservation techniques were not followed, the samples could be contaminated, the quantity of plasma available for each sample was also limited, only 1 ml of plasma was available for each sample as opposed to 10 ml of plasma typically used in such protocols, which could impact detection sensitivity.
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How does a blood test for cancer diagnosis work?
In a study published in Science in April, researchers claimed that blood tests along with imaging tests were able to detect tumors and some at very early stages in women without a history of cancer or symptoms.
In this study, researchers noted that all tumors, no matter the size, maintain a connection with the bloodstream since tumors pull out nutrients from the blood. This means, sometimes, proteins and genetic material spill out from the tumor into the bloodstream, making it possible to detect their presence through certain types of blood tests, also referred to as “liquid biopsies”.
The US National Cancer Institute (NCI) defines liquid biopsies as, “A test done on a sample of blood to look for cancer cells from a tumor that are circulating in the blood or for pieces of DNA from tumor cells that are in the blood.”
Using such blood tests cancers can be detected at early stages, which means treatments can be planned for earlier, given that cancer treatments are more successful when the disease is detected early on.
How is cancer typically diagnosed?
Typically, cancers are detected when individuals present themselves with certain symptoms, post which a number of tests are used for diagnosis such as laboratory tests, tumor biopsies and diagnostic imaging among others.
The researchers from the Nature study note that the five types of cancer studied by them account for over 260,000 cancer deaths in the US each year and 2.1 million yearly cancer deaths in China, therefore “early detection could greatly reduce deaths from these diseases.”
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