breakthrough blood test aims to redefine early detection of cancer
8 minute read
using ai technology, the blood taken as part of the galleri test undergoes an examination that seeks out signs, or signals, of cancer patterns in the dna of cells that have been shed into the blood following cell death.
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advancements in cancer screening have continued to improve outcomes for the 44 per cent of canadians who have, or will go on to develop cancer in their lifetime. current tests, such as mammograms, pap tests, colonoscopies and prostate-specific antigen (psa) blood tests, have all contributed to early diagnoses, resulting in higher survival rates and reduced mortality.
now, there’s a new player in town: the galleri test, created by grail, a biotechnology company based in the united states. this test, which detects over 50 types of cancer, requires only a single blood draw.
the test, which has undergone several clinical trials to get where it is today, is now officially available in canada through medcan, a health and wellness company specializing in preventive care.
“it’s very unlike other sorts of cancers in terms of the technology and what we’re looking for, but at a conceptual level, we’ve been looking for cancer for decades and screening for cancers as much as we can,” said dr. peter nord, chief medical officer (cmo) with medcan. “an ounce of prevention is worth a pound of cure.”
how the galleri test works
when a person is interested in whether or not they have cancer markers, they get the test; all that’s required of them is a blood draw. but the real magic happens after the blood gets back to the lab.
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using ai technology, the blood undergoes an examination that seeks out signs, or signals, of cancer patterns in the dna of cells that have been shed into the blood following cell death. the complex test was made possible by the fact that cancer, in and of itself, is “simple.”
“cells start to divide and grow at a very, very high rate, and so that’s where tumours are created from certain different types of cells that just go a bit crazy, and they grow really fast,” said dr. nord. “when that happens, they also die very fast, and so their dna, that specific dna associated with the cells that have died around cancer, especially, they go into the blood system.”
essentially, when a cancer cell dies in the body, the dna from that cell begins its own trip through the bloodstream. now that technology has been able to catch up to follow along on that trip, it’s easier to see if cancer exists within the body even if someone feels completely healthy.
the cancer signals don’t just determine if there’s cancer, though.
“it’s then able to recognize whether the cancer site of origin is considered to be a pancreatic cancer site of origin, a liver cancer site of origin, an esophageal or a throat cancer site of origin,” said justin lorentz, certified genetic counsellor and interim lead for genetics at medcan. “so, the value is that a cancer is that a) cancer is detected and b) the origin is predicted.”
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according to dr. nord, the test puts a “spotlight” on where to look, illuminating the path to the areas that require the most attention.
the pathfinder 2 study
to understand that spotlight, grail conducted the pathfinder 2 study, a multi-cancer early detection study, to understand and validate the galleri blood test’s contribution to early detection and diagnosis, as well as improved patient outcomes.the initial results of the study showed four important data points:
- the test found as many as seven times more cancer types when it was used in conjunction with standardized testing and routine testing
- it’s especially sensitive to cancers that are the most deadly and often lack adequate screenings
- the level of accuracy is high for many cancers, but not all
- it detects the existence of cancer, as well as the location it originated, to speed up the diagnostic process
pathfinder 2 is an ongoing study with more than 35,000 participants—all over the age of 50 and having showed no previous signs of cancer.
when evaluating the detection accuracy of the galleri test, the pathfinder 2 study looked at over 50 cancers and found that the sensitivity—the probability of a positive result—varies by cancer type.
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when looking at sensitivity for types of cancer, the overall sensitivity ranges from 34.8 per cent with bladder cancer, all the way up to 93.5 per cent with liver or bile duct cancer. on average, the test can accurately detect the 12 cancers responsible for the majority of u.s. cancer deaths at a rate of 76.3 per cent.
accuracy in cancer detection and diagnosis
other metrics are also essential to consider when evaluating the test’s capabilities and limitations: the likelihood of having cancer when given a positive result and the likelihood of not having cancer when given a negative result.
according to lorentz, the galleri test has a high predictive value when a positive cancer signal is detected, sitting at around 60 per cent.
“this means that people can be very confident and clinicians can be very confident when we get a cancer signal detected … that this person really does have cancer,” he said.
the negative predictive value, or false-negative test, is also something people and their clinicians can feel reassured about, because when someone has a negative result with the galleri test, they can be 99.1 per cent sure they don’t have cancer.
“these values are quite significant, and they make this a really promising test,” said lorentz.
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one of the most critical aspects of the galleri test also revolves around the types of cancers it detects, given how deadly they are and how often they are caught in later stages. up until now, screening tests have been largely unavailable, and symptoms are all but nonexistent until the cancer has spread to dangerous levels.
for example, pancreatic and lung cancer are both considered to be among the deadliest cancers in canada because they are often diagnosed in the later stages. but with galleri, these cancers can be detected at rates of 83.7 and 74.8 per cent, respectively, earlier in their progression. this allows people not only to find out about them sooner but also to get into treatment earlier.
looking at pancreatic cancer specifically, the five-year survival rate (the rate of survival five years past diagnosis) in canada sits at only 10 per cent. but it doesn’t have to be that low with better screening.
“when you get pancreatic cancer early, it can be a surgical cure,” said dr. nord. “you can go in, take out the tumour, and by that point you know before it’s actually even spread in the body. so, that’s super exciting.”
ovarian cancer is another that can slip through the cracks because of how it develops and affects people. even small tumours can be missed on ultrasounds, and once they become obviously visible and symptoms develop, it’s often too late to treat effectively.
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with the galleri test, it’s like “looking very, very aggressively like a fine-tooth comb” for anything that resembles or appears to be cancer. the sensitivity for ovarian cancer with the galleri test is also high at 83.1 per cent.
at medcan, the test is currently being used, and is already showing promise for real patients.
“we are still in the early stages of implementing the galleri test, but it has already demonstrated the ability to accurately detect a cancer signal and the cancer site of origin. for example, when the test has indicated the pancreas as the likely origin, follow-up diagnostic testing confirmed pancreatic cancer,” said dr. nord.
better cancer screening and outcomes
while the news of this test’s capabilities is an impressive feat of medical innovation, it is not designed to take over and become the be-all and end-all of cancer screening. it won’t act as a replacement, but rather another tool that the medical community and their patients can use to improve health outcomes, regardless of the cancer they develop.
because the screenings that exist have already been improving lives, it will simply act as another option for people who want to act first instead of later when it comes to their potential cancer status.
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“who knows where the technology is going to lead us in the future, but currently, it’s not going to replace anything. it’s complementary, and the more that you can have several tests all coming together, the overall accuracy goes way up,” said dr. nord. “the synergies between these different screening tests are really amazing.”
the limitations in terms of varying accuracy rates also make it more of a complementary test than the only screening test that matters, because not all cancers will spread dna in the same way.
“the cancers that are close to a blood supply, and that’s part of their natural progression, we’re going to see higher rates of dna shed, whereas cancers that are, we call it encapsulated or kind of don’t spread (and) hang out in one spot, things like prostate cancer or really early stage breast cancer, they’re less likely, we believe, to be shedding dna, and so therefore, less likely to be picked up through this blood test,” said lorentz. “thankfully, they can be picked up through psa blood tests or mammograms, but there are some cancers that, just based off of how they grow, this test may not be the most sensitive at identifying them.”
galleri, while available in the u.s. and select areas of canada (ontario), and being assessed in the united kingdom, is also still just learning to walk. for it to become first-line screening and be available through publicly funded healthcare, specific trials and investigations need to be conducted first.
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according to lorentz, that’s what the assessments in the u.k. are currently about, but because the technology is so new, it’s not yet there when it comes to “public expansion.”
that said, it doesn’t change what it can do as an added measure of cancer detection, and where the technology can go from here.
“it’s really filling a niche gap, and nobody planned that. it just sort of worked out that way,” said dr. nord. “it’s a really special test and that’s why we’re really excited about it.”
according to lorentz, the tool is novel, but the more that’s known about the test and its potential, and the better-studied it is, the more it could open a really important door for cancer screening.
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