Early detection of cancer using a blood test

The doctor holds blood tubes in his hand. Blood test conce… | Flickr
Simple Blood test for cancer detection? Picture courtesy: Flickr

Blood test is one of the simplest, yet most informative weapons in your doctor’s arsenal. A tiny needle prick and a few millilitres of blood can help doctors 1) evaluate how your body’s vital organs like heart, liver, kidneys and thyroid are functioning, 2) diagnose diseases such as diabetes, cancer, heart disease and communicable diseases etc, 3) diagnose any deficiencies you might have like vitamin or iron deficiencies, and 4) to check if your medication is working.

Earlier the better

It is no secret that when it comes to the diagnoses and treatment of cancer, earlier the better. The survival rate significantly increases when cancer is detected and treated at an early stage – the average 5- year survival rate at early stage is 91%, while average 5-year survival at late stage is 26%. Currently, there are a few screening tests available for a few types of cancers such as colonoscopy (bowel cancer), prostate specific antigen (prostate cancer), mammography (breast cancer), and cervical cytology (cervical cancer).  Cancer screening is important because they help in diagnoses and treatment of several types of cancers early, before they cause symptoms. Early detection is important because when abnormal tissue or cancer is found early, it may be easier to treat. By the time symptoms appear, cancer may have begun to spread and becomes much harder to treat.

An ideal cancer screening method would be the one where the cancer is detected years before you show any symptoms. And if the screening procedure is non-invasive and can be done using a simple blood test, that would be icing on the proverbial cake! A new research published in the journal Nature Communications promises just that.

Using a blood based cancer screening method, the scientists in this paper were able to detect five common types types of cancer including stomach, esophageal, colorectal, lung and liver up to four years earlier than normal methods would! This suggests that people with cancer would test positive while asymptomatic (when they do not show any symptoms), years before they develop more visible, serious illness.

This method detects cancer by utilizing a biological process called methylation (addition of a chemical called methyl to the DNA which modifies its function) of circulating tumor DNA. Let’s break it down a bit…

Circulating tumor DNA (ctDNA)

File:Circulating-tumor-dna-article. v300237192.jpg
Picture courtesy: Wikimedia Commons

In the recent years ctDNA in blood plasma has become a promising cancer biomarker. ctDNA is found in the bloodstream and refers to the small pieces of DNA that comes from cancer cells. Most DNA is inside a cell’s nucleus. As a tumor grows, cells die and are replaced by new ones. The dead cells get broken down and their contents, including DNA, are released into the bloodstream. The quantity of ctDNA varies among individuals and depends on the type of tumor, its location, and for cancerous tumors, the cancer stage.

DNA methylation

DNA methylation is a chemical modification of the DNA. It is a biological process by which methyl groups are added to the DNA molecule. Methylation can change the function of a DNA without actually changing the sequence. DNA methylation is essential for normal development and is associated with a number of key cellular processes including aging as well as cancer development.

The assay

The scientists developed a highly specific assay to identify these unique DNA signatures(changes in DNA) on ctDNA in blood. The unique nature of this study is that the researchers had access to blood collected from 123,115 healthy subjects aged 25 to 90 years for long term storage for nearly 10 years.  These individuals were then indefinitely monitored for cancer occurrence through linkages with local cancer registries and health insurance databases. A total of 575 initially healthy subjects (who presented as asymptomatic) were diagnosed with one of five common cancer types within 4 years of initial blood draw. (This was 95% of the people who were initially healthy/asymptomatic but later went on to develop cancer). As a proof of concept they also tested blood from 113 patients who were already diagnosed with one of the five common cancers using this assay. The test was able to accurately detect cancer in 88% of these samples indicative of the efficiency of the assay.

Bottomline

This study has presented a new non invasive method for early detection of five common types of cancer upto 4 years earlier than conventional methods. Whether this assay will improve patient outcomes remains to be seen. Further and the most important caveat is that this assay is meant for people who have already developed cancer but are asymptomatic. Because it is based on detecting particles in blood which are produced by cancer cells already present in the body. It cannot however, be used as prognostic tool to predict if healthy individuals will develop cancer in the future. Nevertheless, if this method can detect cancer 4 years before other conventional methods I would still call it remarkable!

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