The leading cause of death worldwide, cancer killed at least 7.6 million people in 2008, accounting for a staggering thirteen percent of all deaths globally. With no signs of abating, the number of international cancer deaths is projected to increase by forty-five percent in the next decade.

The majority of deaths involving this disease are caused primarily by lung, breast, colorectal, stomach, or liver cancers, exacerbated by a lack of prevention or the late-stage of diagnosis. This is because late-stage cancers often lack treatment options, whereas survival rates increase significantly when cancer is identified in the early stages of the disease, as there is a heightened possibility the tumor can be surgically removed or treated with therapeutics.

Giving cancer patients more time

On average, the chances of surviving five-years at the early stage of cancer is ninety-one percent, while the average 5-year survival rate at the late stage plummets to approximately 26 percent. Taken together, this makes the detection of tumors at the earliest possible stage of paramount importance for successful cancer treatment, with the majority of cancer types currently lacking an effective non-invasive early screening option.

Recently, tumor DNA (ctDNA) circulating in blood plasma has garnered much interest as a non-invasive biomarker. However, the amount of cancer DNA in plasma is limited, leading to dampened sensitivity and errors; a fact inflamed by the multitude of possible cancer mutations to be screened.

Now, a study from researchers led by UC San Diego develops a non-invasive blood test capable of detecting circulating tumor DNA methylation to identify whether a person has one of the five most prevalent forms of cancer, up to four years before diagnosis. The team states their diagnostic can detect cancer by targeting a limited number of genomic regions aberrantly methylated across different cancer types. This allows their test to be used as an inexpensive cancer screen from only a single vial of blood, unlike the more costly ctDNA which works by identifying a legion of inconsistent mutations. The opensource study is published in the journal Nature Communications.

Earliest ever detection of cancer

Previous studies show the survival of patients increases significantly when cancer is identified at its earliest possible inception, as this raises the prognosis for surgical removal and/or therapeutics. Only a limited amount of early cancer screening tests exist for a minute number of cancer types, however. This means an effective screening test must demonstrate cancer detection without the patient exhibiting any symptoms years before conventional diagnosis if cancer mortality rates are to be vastly improved.

Recent studies from the group have investigated methods to detect cancer based on DNA methylation analysis, involving the identification of the DNA signature called CpG methylation, which is the addition of methyl groups to multiple adjacent cytosine-guanine sequences in a DNA molecule.

It is in this way each tissue in the body can be identified by its unique signature of methylation. The current study develops a non-invasive blood test for the detection of circulating tumor DNA methylation able to detect cancer four years before conventional diagnosis methods.

Detecting asymptomatic cancer

The current study uses samples from the Taizhou Longitudinal Study, where plasma samples were collected from over 120,000 individuals between 2007 and 2017 to be monitored for cancer occurrence. Once a person was diagnosed with cancer, the researchers had access to blood samples taken one to four years before these patients started to show symptoms.

Specifically, blood plasma samples from 605 participants exhibiting no symptoms (asymptomatic) were used in this study, 191 of these were later diagnosed with colorectal, esophageal, liver, lung, or stomach cancer within four years of their blood being taken and stored.

Results show the new test, dubbed PanSeer, detects cancer in ninety-five percent of asymptomatic individuals who were later diagnosed. The test also has the ability to detect five common types of cancer in eighty-eight percent of patients after diagnosis with a specificity of 96 percent.

Data findings show Panseer accurately detects colorectal, esophageal, liver, lung, or stomach cancer in eighty-eight percent of samples from 113 participants who were already diagnosed when the samples were collected.

The lab states their diagnostic also recognized cancer-free samples ninety-five percent of the time. They emphasize their assay cannot predict which patients will later go on to develop cancer, rather it identifies patients who already have cancerous growths whilst remaining asymptomatic for current screening methods.

Getting the test to the public

The team surmises they have successfully demonstrated cancer can be non-invasively detected up to four years before the current standard of care. For the future, the researchers state further large-scale longitudinal studies are needed to confirm the potential for the early detection of cancer in patients exhibiting no symptoms.

Source: UC San Diego News Center

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