A major Canadian clinical trial aims to determine whether simple blood tests can detect returning cancer months before conventional scans, potentially giving thousands of patients access to earlier treatment while reducing unnecessary therapies.
Researchers at the University Health Network in Toronto have launched a five-year study involving more than 7,000 cancer survivors to evaluate so-called liquid biopsies. The blood tests search for tiny fragments of tumour DNA circulating in the bloodstream after patients complete treatment, offering a possible early warning that cancer has returned.
The project, known as SHERLOCK, will recruit patients who have already undergone treatments intended to cure their disease. Scientists hope the trial will show whether detecting circulating tumour DNA before it appears on imaging scans can improve patient outcomes and eventually become part of routine cancer care.
Toronto resident Paul Lonergan experienced the potential benefits of the technology after doctors diagnosed him with a large tumour at the base of his tongue in 2023. Following seven weeks of radiation therapy and chemotherapy, his medical team used a liquid biopsy through a clinical trial to determine whether any cancer remained.
Although standard examinations suggested the treatment had succeeded, the blood test detected lingering tumour DNA. Doctors subsequently offered Lonergan experimental immunotherapy, and later liquid biopsies found no remaining traces of cancer in his bloodstream.
Today, access to liquid biopsy monitoring remains limited across Canada. Most patients can only receive the tests through research studies or private clinics that often charge thousands of dollars.
However, researchers believe that could eventually change.
Read more: Breath Diagnostics advances pre-op pneumonia screening with FDA breakthrough designation
Read more: Breath Diagnostics leaders promote their mission at Miami investment conference
Researchers searching for patients with early evidence of relapse
Dr. Lillian Siu, senior scientist at University Health Network’s Princess Margaret Cancer Centre and one of the scientific leaders at the Peter Gilgan Centre for Early Cancer Detection Research, leads the SHERLOCK study.
She said the research focuses on detecting molecular evidence that cancer may return before doctors can identify it using routine physical examinations or computed tomography scans. According to Siu, finding those warning signs earlier could allow physicians to intervene sooner while curative treatment remains possible.
Additionally, researchers plan to connect patients showing early evidence of relapse with other clinical trials investigating new therapies.
Those experimental treatments could include immunotherapy, newly developed cancer drugs or glucagon-like peptide-1 medications, commonly known as GLP-1 drugs, to determine whether they can eliminate remaining disease before tumours become visible.
The researchers also want to answer another important question.
Some patients may not require aggressive follow-up treatments if repeated blood tests show no evidence of residual disease. Siu said the trial will examine whether liquid biopsies can safely identify those individuals, potentially sparing them from invasive procedures and additional side effects.
Liquid biopsy technology has existed for slightly more than a decade. Scientists first coined the term in 2010, and the first U.S. regulatory approval followed several years later.
Initially, the technology required much larger fluid samples than today’s tests.
Furthermore, improvements in laboratory techniques now allow researchers to detect minute amounts of tumour DNA using ordinary blood samples. Those advances have greatly expanded interest in monitoring patients after cancer treatment rather than relying solely on imaging or physical examinations.
Read more: Prestigious medtech intelligence firm recognizes Breath Diagnostics for innovation
Read more: Breath Diagnostics completes install of advanced mass spectrometry system
Liquid biopsies do not produce perfect results
Researchers have already published studies suggesting liquid biopsies can identify minimal residual disease after surgery for several types of cancer. Other research has associated earlier detection of tumour DNA with longer survival and lower risks of disease progression.
Meanwhile, at least one Ontario hospital already uses liquid biopsy technology as a diagnostic tool. New Brunswick also introduced liquid biopsies for monitoring lung cancer patients during 2024.
Dr. Ramy Saleh, a medical oncologist and cancer researcher at the McGill University Health Centre, believes liquid biopsies could fundamentally change how doctors monitor cancer survivors.
He said researchers describe current knowledge as only the beginning of what may become possible.
However, several experts caution that important scientific and practical questions remain unanswered.
Dr. Christopher Booth, a Queen’s university based medical oncologist, said liquid biopsies raise complex ethical issues alongside their medical promise.
He questioned whether every patient in remission would want to learn that microscopic traces of cancer might still circulate in their bloodstream despite clear imaging results. Some patients, Booth said, may welcome that information because it allows them to prepare and pursue additional treatment. Others, however, may find the uncertainty emotionally overwhelming.
Additionally, liquid biopsies do not produce perfect results.
Booth explained that false positives can indicate tumour DNA when no active cancer exists. Conversely, false negatives may fail to detect disease that continues developing elsewhere in the body.
Those possibilities can create considerable psychological stress for patients receiving repeated test results over several years.
Read more: Breath Diagnostics leader speaks at lung cancer education event in Louisville
Read more: Breath Diagnostics opens Respiratory Innovation Summit with captivating presentation
Enthusiasm surrounding liquid biopsies occasionally exceeds evidence
Researchers also emphasize that liquid biopsies require ongoing monitoring rather than a single blood test.
Instead, patients generally need repeated testing every three to four months. Scientists still need additional evidence to determine the best testing schedules for different cancers and patient populations.
Meanwhile, enthusiasm surrounding liquid biopsy technology has occasionally exceeded the available evidence.
One widely publicized screening test, Galleri, developed by privately held Grail Inc (NASDAQ: GRAL), failed to achieve its primary goal in a major United Kingdom clinical trial earlier this year. Researchers reported the test did not significantly reduce diagnoses of advanced Stage 3 and Stage 4 cancers, disappointing hopes for widespread adoption through the country’s public health system.
Despite those results, some Canadian private clinics already market multi-cancer blood tests to healthy individuals. Prices can exceed CAD$2,000, even though Health Canada does not regulate privately developed laboratory tests and the Galleri test lacks formal approval from Canadian and U.S. health regulators.
Saleh said affordability represents one of the biggest barriers preventing broader adoption.
He noted that patients undergoing surveillance often require repeated testing throughout the year. Meanwhile individual liquid biopsy tests can cost approximately CAD$5,000. Those expenses place the technology beyond the reach of many patients without research funding or insurance coverage.
Furthermore, Saleh believes large clinical trials could eventually demonstrate that earlier detection improves outcomes while reducing overall healthcare costs. If researchers produce convincing evidence, public health systems may decide the tests deserve routine funding for cancer survivors.
.
