Summary
This article covers SHERLOCK, a Canadian clinical study using liquid biopsy technology to detect molecular residual disease (MRD) in cancer patients treated with curative intent. It explains what ctDNA is, why early detection of recurrence matters, what the current evidence shows, and where the technology's limitations still lie.
If you’ve ever been treated for cancer and told you were in remission, you’ll know the hardest part often isn’t the treatment. It’s the waiting. The scans. The appointments. The quiet, persistent anxiety about whether the cancer is truly gone, or whether it’s quietly growing somewhere no one can see yet.
A new Canadian clinical study is working on an answer to exactly that question.
The Scale of the Problem
Cancer touches virtually every Canadian family. In 2024, an estimated 247,100 new cancer cases and 88,100 cancer deaths were projected in Canada, with a lifetime probability of developing cancer sitting at 45%. Survival rates have improved significantly, but survival creates its own challenge: a growing population of people in remission who live with the uncertainty of whether their cancer will return.
For many cancer types, recurrence is a genuine risk. Almost one third of patients with operable colorectal cancer recur after surgery, and standard scans and blood markers often can’t detect cancer until it has already grown large enough to be visible. By that point, treatment options may be more limited.
That’s the gap SHERLOCK is designed to close.
What Is SHERLOCK?
SHERLOCK (Study of High-Precision Evaluation of Molecular Residual Disease Through a Platform for Cancer Tracking and Interception) is a Canadian platform study collecting blood, tissue, urine, and saliva from patients treated with curative intent across multiple cancer types. It uses those samples to detect circulating tumour DNA (ctDNA), fragments of tumour DNA that shed into the bloodstream and can be picked up through a blood draw, commonly called a liquid biopsy.
The goal is early cancer interception: detecting signs of recurrence at a molecular level, before anything appears on a scan, and using that information to guide clinical decisions and connect patients to early intervention trials.
What the Evidence Already Shows
The research behind this approach is building quickly, and some of the most compelling recent data comes from Canada itself.
At the American Association for Cancer Research Annual Meeting in April 2025, researchers from BC Cancer in Vancouver presented interim results showing that a ctDNA liquid biopsy assay detected signs of recurrence in colorectal cancer patients before any imaging could. All patients who eventually experienced clinical recurrence were ctDNA-positive before their scans confirmed it, by a median of 198 days earlier. One patient had ctDNA recurrence detected 416 days before clinical confirmation.
That is not days ahead of a scan. That is months, sometimes more than a year, during which a patient and their care team could potentially act rather than wait.
A 2026 review published in PMC confirmed that ctDNA has demonstrated considerable potential in early cancer detection, monitoring of therapeutic responses, and assessing minimal residual disease to predict recurrence. The technology is already in routine clinical use for certain advanced cancers, including non-small cell lung cancer. SHERLOCK is working to extend that capability to earlier-stage disease, to patients treated with the goal of cure.
What It Doesn’t Do Yet
It’s worth being clear. ctDNA testing still has limitations: sensitivity remains a challenge for very small tumours, and researchers note the technology is currently more reliable for prognosis and disease monitoring than for primary early detection. SHERLOCK is a research study, not yet a standard-of-care test, and the path to routine clinical use in Canada requires regulatory review, health technology assessment, and provincial coverage decisions.
But the trajectory is clear, and Canada is actively helping to shape it.
The Bottom Line
For the hundreds of thousands of Canadians living after a cancer diagnosis, the question of recurrence is never far away. SHERLOCK and the liquid biopsy research behind it represent a genuine shift in what might be possible: catching cancer’s return in the blood, before it appears anywhere else.
That’s not a cure. But for someone in remission, knowing sooner is everything.
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