Determine the presence and cause in a single test
In the long effort to match cancer patients with the treatments most likely to help them, a team at the University of Toronto has developed a single genetic test — MultiMMR — that identifies both the presence and cause of mismatch repair deficiency in tumor cells, consolidating what once required a cascade of separate analyses. The significance lies not only in efficiency but in equity: patients whose diagnoses previously fell through the cracks of multi-step testing may now receive the immunotherapy access or genetic counseling they were owed. As universal cancer screening becomes standard practice, this kind of diagnostic clarity may quietly reshape the pace and precision of oncological care.
- Diagnosing mismatch repair deficiency has long required multiple tests across different labs, creating delays and blind spots at moments when treatment decisions cannot wait.
- Patients with inconclusive or incomplete results have risked being denied immunotherapy or missing inherited cancer risk counseling — consequences that compound across families.
- MultiMMR consolidates five distinct types of MMR analysis into a single procedure using minimal DNA, achieving 95–97% concordance with current clinical standards.
- In validation studies, the test identified MMR deficiency in 29 patients whose prior testing had been incomplete, recovering cases the standard cascade had failed.
- With colorectal and endometrial cancer screening expanding rapidly, existing multi-step protocols are already under strain — MultiMMR is positioned to meet that rising demand.
Researchers at the University of Toronto have developed MultiMMR, a single integrated genetic test that identifies mismatch repair deficiency in cancer cells — and determines why it exists — from a minimal DNA sample taken from tumor tissue.
Mismatch repair genes act as the cell's proofreaders, correcting errors that accumulate during normal cell division. When these genes fail, whether through inherited mutation or cancer-driven silencing, cells mutate at an accelerated rate. This deficiency matters clinically because tumors carrying it respond unusually well to immunotherapy, a class of drugs that trains the immune system to attack cancer cells. Knowing a patient's MMR status has become essential to treatment planning.
Until now, reaching that diagnosis reliably meant ordering a cascade of separate tests — each examining a different aspect of MMR function, each requiring different expertise, and each capable of missing what another might catch. Results were sometimes inconsistent, and some patients required repeat testing, delaying decisions at the worst possible time.
MultiMMR screens simultaneously for five types of MMR abnormalities: promoter methylation, mutations, copy number changes, copy neutral loss of heterozygosity, and microsatellite instability. Validated against 142 specimens from patients with colorectal, endometrial, and brain cancers, it achieved 95% concordance on methylation detection and 97% on microsatellite instability. It also correctly identified all 11 mutations in a synthetic control sample designed to include variants that standard sequencing routinely misses.
Most strikingly, MultiMMR identified MMR deficiency in 29 patients whose prior testing had been incomplete or inconclusive — individuals who might otherwise have been denied immunotherapy or missed the chance for inherited risk counseling and family surveillance.
As universal tumor screening becomes standard practice and demand for MMR testing rises sharply, the old multi-step protocols are already straining. MultiMMR addresses that bottleneck while giving clinicians faster, more complete information — and making better use of scarce biopsy material in the process. Published in the Journal of Molecular Diagnostics, it represents the kind of diagnostic advance that reshapes not just how oncologists work, but how quickly they can act on behalf of their patients.
A team of researchers at the University of Toronto has developed a single genetic test that can identify whether a patient's cancer cells have defective mismatch repair—and crucially, why. The test, called MultiMMR, consolidates what has traditionally required multiple separate analyses into one streamlined procedure, working from a small DNA sample taken from tumor tissue.
Mismatch repair genes function as the cell's proofreaders. They catch and fix the tiny errors that slip into DNA during normal cell division. When one or more of these genes stops working—either because of an inherited mutation or because the cancer itself has disabled them—cells accumulate mutations at an accelerated rate. This creates what's called mismatch repair deficiency, or MMR deficiency. The discovery matters because tumors with this deficiency respond remarkably well to a newer class of cancer drugs called immunotherapies, which train the immune system to recognize and attack cancer cells.
The problem, until now, has been that diagnosing MMR deficiency reliably has been messy. Clinicians have had to order a cascade of different tests—some looking for genetic mutations, others checking for epigenetic changes like promoter methylation, still others measuring microsatellite instability. Each test requires different expertise and different lab procedures. Results can be inconsistent. Some genetic variations slip through the cracks entirely. A patient might need to come back for additional testing, delaying treatment decisions at a moment when speed matters.
MultiMMR performs all of these analyses simultaneously from a single DNA sample. The test screens for five different types of MMR abnormalities: promoter methylation, mutations, copy number changes, copy neutral loss of heterozygosity, and microsatellite instability. In validation studies, researchers sequenced DNA from 142 specimens—82 normal samples and 60 tumor samples from 82 patients with colorectal, endometrial, and brain cancers. When they compared MultiMMR results to conventional clinical testing in 45 patients, the new test achieved 95 percent concordance on promoter methylation detection and 97 percent on microsatellite instability. For identifying the specific genetic variants causing MMR deficiency, MultiMMR matched clinical results in 23 of 24 cases. The test also correctly identified all 11 mutations in a synthetic control sample designed to include variants that are notoriously difficult for standard next-generation sequencing to catch.
Perhaps most significantly, MultiMMR identified MMR deficiency in 29 patients whose previous testing had been incomplete or inconclusive—cases where the standard cascade approach had failed them. These are patients who might have been denied access to immunotherapy or missed the chance for genetic counseling and surveillance if they carried an inherited form of the deficiency.
The timing of this development is not incidental. As colorectal and endometrial cancer screening expands, demand for MMR testing is rising sharply. Many hospitals and labs are moving toward universal tumor testing—screening every patient's cancer for MMR status as a matter of routine. The old multi-step protocols are already straining under the load. Many next-generation sequencing tests in current use don't even screen for microsatellite instability or promoter methylation alongside mutations, creating blind spots in diagnosis.
MultiMMR addresses this bottleneck while also improving clinical utility. Because the test determines both the presence and the cause of MMR deficiency in one analysis, it gives clinicians the information they need to make faster treatment decisions. For patients with inherited MMR deficiency, it enables genetic counseling, surveillance protocols, and testing of relatives—interventions that can catch cancer earlier or prevent it altogether. The streamlined workflow also makes better use of limited tissue samples, a practical consideration in cases where biopsy material is scarce.
The research appears in the Journal of Molecular Diagnostics. As universal tumor testing becomes standard practice, tests like MultiMMR may become essential infrastructure—the kind of diagnostic tool that quietly reshapes how oncologists work, how quickly they can act, and ultimately how well they can match patients to the treatments most likely to help them.
Citações Notáveis
Tumors with MMR deficiency respond well to new cancer immunotherapies, and determining whether an individual has an inherited form can allow clinicians to enroll patients in surveillance and provide genetic testing to relatives.— Trevor J. Pugh, lead investigator, University of Toronto
MultiMMR streamlines the process and distinguishes the type of MMR deficiency with improved turnaround time, can scale well with increasing demands, and can provide clinicians with important information to inform patient management.— Leslie Oldfield, lead author, University of Toronto
A Conversa do Hearth Outra perspectiva sobre a história
Why does it matter that this test does everything at once instead of in steps?
Because time and tissue are both precious in cancer care. If a patient needs three separate tests, that's three separate procedures, three separate waits for results. Meanwhile, their tumor is growing. And if you only have a small biopsy sample, running multiple tests can exhaust it before you get the answers you need.
But the old tests work, don't they? Why replace something that's already proven?
They work inconsistently. Some genetic variations hide from standard sequencing. Some labs miss methylation changes entirely because they're not screening for them. A patient can fall through the cracks—get told their tumor doesn't have MMR deficiency when it actually does, and miss out on immunotherapy that could help them.
What happens if you get the diagnosis wrong?
If you say someone has MMR deficiency when they don't, they might get a drug that won't help them. If you say they don't have it when they do, you've just denied them access to a treatment class that works well for their cancer. And if it's inherited, you've also missed the chance to warn their relatives.
So this test is mainly about speed and accuracy?
It's about those things, but also about completeness. It looks at five different types of abnormality in one go. The old cascade approach was like checking different systems in a house separately—electrical, plumbing, foundation—and sometimes missing the connections between them.
Who benefits most from this?
Patients with colorectal and endometrial cancer, primarily. But also their families, if the deficiency is inherited. And clinicians—they get clearer answers faster, which means better treatment decisions. And hospitals managing rising demand for testing.