New blood test can help detect cancer early

Tuesday, 13 June 2023 (12:36 IST)
When he received the diagnosis, it was already too late. The cancer had eaten away at the patient's pancreas and spread out to neighboring organs. Surgery was no longer an option. Four months later, at the age of 31, the young man from Germany was dead.
Even though cancer treatment has improved in recent years, therapy often fails because tumors are detected too late. Especially at an early stage, symptoms like stomach pain or fatigue are often vague, making patients see a doctor only when the disease is already hard or impossible to treat.
A blood test called Galleri aims to change this narrative. The developers from American healthcare company Grail say the test is able to detect more than 50 different cancers in a simple blood sample. Earlier this month, scientists presented results from a Galleri study at the world's largest cancer conference, the annual meeting of the American Society of Clinical Oncology (ASCO).
2 out of 3 times the test got it right
The research team, led by scientists from the University of Oxford, had used the test in more than 5,400 patients showing symptoms indicating that they might have cancer. Before receiving the standard diagnostic exam, patients also gave a blood sample for evaluation with the Galleri test. In two out of three patients who were ultimately diagnosed with cancer through standard diagnostics, the blood test detected a cancer signal as well.
However, the test also said that 79 participants had cancer when they didn't — making them so-called false positives.
"They can be problematic," Mark Middleton, the lead researcher of the study, told DW. "The risk is that you turn a healthy individual into a patient by tagging them with a label that's incorrect."
This situation can be highly stressful for patients and healthcare professionals alike — emotionally and economically.
The potential: Facilitate faster testing and possibly therapy
Nonetheless, many researchers and clinicians are excited about the idea of a blood test that could help with early detection. When cancer is detected early, before it has spread, patients' survival rates are much higher than when the disease is diagnosed in later stages. 
Another advantage of the Galleri test: It looks for more than 50 different cancers, including ones that are usually detected very late and have poor survival rates, like ovarian or pancreatic cancer. The list also includes cancers for which there is currently no routine screening.
Detecting fragments of tumor DNA in the blood
So how does the test work? When a cell dies, its DNA is shed into the bloodstream. The DNA of cancer cells is different from that of healthy cells in that it has specific markers. More precisely: A specific pattern of methylation.
"There are patterns that are typically only found in cancers," Niels Halama from the German Cancer Research Center, who was not involved in the Galleri study, told DW.
The Galleri test is able to detect these patterns. 
The pattern differs from cell type to cell type, so the test results also indicate where in the body the cancerous cells come from. This way, the researchers were able to say where the tumor was located 85% of the time. 
"That can be hugely useful in making sure you do the right tests," Middleton said.
If, for example, the test flags pancreatic cancer, clinicians can immediately do specific testing for this cancer to confirm the diagnosis — without wasting valuable time and money looking for other diseases.
Still a work in progress
Scientists aren't hailing the test a breakthrough quite yet though. The Galleri test is tricky: It does not work like other tests, with thresholds above or below which a specific condition is present or not. Rather, it's a pattern decoder.
"It's like looking at a picture. You can see a picture of the Mona Lisa and say: 'OK, it's the Mona Lisa.' And you can have a picture from Vermeer and say: 'OK, that's not the Mona Lisa.' But there's all sorts of in between," Halama said.
Right now, the test is a learning machine: With each new sample, the whole system gets better. At least that's what the researchers hope.
(As always) there are caveats 
At the moment, the test's strength is that it triggers further testing at an early point in time. Not more. As lead researcher Middleton pointed out: "A positive test result is not a diagnosis of cancer. It says: Do more tests to find the cancer!" 
One limiting factor at the moment: The test depends on a certain amount of genetic material being present in the bloodstream. If a tumor cell is not producing enough genetic material, the test cannot detect it. 
The Galleri test is also not able to find all types of cancers. One reason: There are tumors without the specific markers needed to be detectable by the test.
"So they will most likely never be detectable with this type of test," said Halama.
The present study only included patients who already had symptoms. It was more accurate in older patients, those with more advanced cancers, and upper gastrointestinal tumors. Future studies will need to show how it will perform in patients without symptoms, less progressed cancers and cancers outside the gastrointestinal tract. 
Right now, scientists are examining whether the Galleri test has the potential to work as a general health screening in a study with 140,000 participants in the UK. Results are expected later this year.

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