How to Read Signatera Test Results: Positive & Negative

A Signatera report comes back as either “positive” (circulating tumor DNA detected) or “negative” (circulating tumor DNA not detected), and that binary result is the single most important line on the page. A positive result means the test found fragments of tumor DNA circulating in your blood, which signals that cancer cells are likely still present somewhere in your body. A negative result means no tumor DNA was detected at that moment, which is generally reassuring but not an absolute guarantee. The story gets more interesting when you look at trends over multiple draws and at the quantitative numbers that accompany a positive result.

What the Report Actually Shows

Signatera is a tumor-informed test, meaning it starts by sequencing your actual tumor tissue to identify up to 16 DNA mutations unique to your cancer. It then builds a custom assay that looks specifically for those mutations in a standard blood draw, with a detection threshold as low as 0.01% variant allele frequency. That is extraordinarily sensitive compared to standard imaging or blood-based tumor markers.

When your results arrive, the headline is the qualitative call: “ctDNA Detected” or “ctDNA Not Detected.” If ctDNA is detected, the report also includes a quantitative measurement, typically reported as mean tumor molecules per milliliter of plasma (MTM/mL). This number reflects roughly how much tumor-derived DNA is floating in your bloodstream. A higher MTM/mL value generally correlates with a larger or more active tumor burden, while a lower value suggests less disease. A large pan-cancer analysis of over 23,000 patients found that MTM/mL and variant allele frequency both correlate with tumor volume and patient outcomes, making these numbers clinically meaningful rather than just abstract lab values.¹

The way MTM/mL is calculated matters at the technical level: the most accurate approach averages across all 16 tested targets rather than only the ones that happened to be detected in a given sample. This method better reflects the true ctDNA concentration, especially at very low levels where only a few targets light up.² For you as a patient, this means the MTM/mL number on your report is designed to be meaningful even when the amount of tumor DNA is tiny.

What a Positive Result Means

A positive Signatera result after surgery indicates that residual cancer cells are releasing DNA into your bloodstream, a state oncologists call molecular residual disease (MRD). In practical terms, it means your risk of the cancer coming back is substantially higher than it would be with a negative result. The strength of that association varies by cancer type, but the direction is consistent across the board.

In colorectal cancer, the evidence is especially strong. A study of stage II and III patients found that ctDNA positivity after surgery was associated with roughly an 11-fold higher risk of recurrence compared to those who tested negative.³ An interim analysis of the BESPOKE CRC study put the hazard ratio even higher, finding that MRD-positive patients had roughly a 21-fold greater risk of shorter disease-free survival than MRD-negative patients.⁴ After adjuvant chemotherapy specifically, the prognostic power was even more striking: one study reported a hazard ratio above 50 for ctDNA positivity detected right after completing chemotherapy.⁵

In breast cancer, a meta-analysis pooling 18 studies and about 1,670 patients found that ctDNA positivity was associated with roughly a 7-fold higher risk of shorter disease-free survival across subtypes and time points.⁶ In the adjuvant setting specifically, the association was even stronger, with a nearly 15-fold increase in relapse risk for ctDNA-positive patients.

For bladder cancer, the pattern holds. In patients who underwent radical cystectomy, detectable ctDNA during the surveillance window was associated with about a 23-fold higher risk of shorter disease-free survival compared to those with undetectable ctDNA.⁷ In the NIAGARA trial studying perioperative treatment for muscle-invasive bladder cancer, ctDNA status shifted dramatically through treatment: about 57% of patients were ctDNA-positive at baseline, dropping to 22% after neoadjuvant therapy and just 9% after surgery.⁸ After cystectomy, the test identified metastatic relapse with about 94% sensitivity and 98% specificity.⁹

A positive result does not mean recurrence is certain. It means the probability is elevated and your oncologist will likely want to act, whether that means starting or intensifying treatment, ordering imaging sooner, or monitoring more frequently.

What a Negative Result Means

A negative Signatera result is broadly good news: it suggests no detectable molecular residual disease. In breast cancer, patients who remain serially negative on ctDNA testing have meaningfully better outcomes, providing real reassurance during what can be years of anxious follow-up.¹⁰ In colorectal cancer, serial ctDNA analyses identified recurrence with an overall accuracy of about 92%.³

But a negative result is not the same as a guarantee that you are cancer-free. Several biological realities can produce a false negative. Some tumors simply do not shed much DNA into the bloodstream, and why this happens is still not fully understood. Brain metastases are a known blind spot because the blood-brain barrier limits how much tumor DNA crosses into peripheral circulation. Subcutaneous metastases have also been shown to be underrepresented in ctDNA analysis.¹¹ Additionally, a standard blood draw yields a limited amount of plasma, which limits the total DNA available for analysis. If the tumor fraction in your blood is very small, the test may not have enough material to pick up those trace signals.

The practical takeaway: a negative result should lower your worry, not eliminate your follow-up. Your oncologist will still recommend imaging and clinical evaluations alongside ctDNA monitoring, especially if your cancer type or stage carries higher baseline risk.

Why Trends Matter More Than Any Single Draw

Perhaps the most important thing to understand about Signatera is that a single blood draw gives you a snapshot. The real power comes from serial testing over time. The trajectory of your ctDNA levels tells a story that no single result can.

In melanoma patients being treated for advanced disease, researchers found that persistent or rising ctDNA levels reliably predicted progression. Among patients who eventually progressed, 100% showed either a rise in ctDNA or continued positivity in the months before progression became visible on imaging. The median lead time between ctDNA changes and clinical progression was over 11 months. On the flip side, patients who achieved durable treatment responses showed sustained ctDNA clearance.¹²

In genitourinary cancers treated with immunotherapy, ctDNA dynamics matched what was happening on imaging about 83% of the time.¹³ Falling ctDNA levels tracked with treatment response, and rising levels tracked with progression. This kind of real-time molecular feedback can help your oncology team assess whether a treatment is working before the next scheduled CT scan.

So when you get a Signatera result, place it in context. If you were positive and now you are negative, that is an encouraging sign of response or clearance. If you were negative and have become positive, that warrants prompt investigation. If you have been negative on several consecutive draws, your risk profile is meaningfully lower than someone who has had intermittent positivity. The overall pattern in ctDNA levels corresponds closely with clinical and imaging outcomes.¹⁴

How Far Ahead Can ctDNA Detect Recurrence Before a Scan

One of the most striking features of ctDNA testing is its ability to detect recurrence before imaging does. In hepatopancreatobiliary cancers (liver, pancreas, bile duct), Signatera detected disease before imaging with a median lead time of about 28 days, though in individual patients the advantage ranged from one month to seven months.¹⁵ In colorectal cancer, the lead time averaged about five months.³ In the melanoma study mentioned earlier, ctDNA changes preceded clinical progression by a median of over 11 months.¹²

This lead time creates a window. Whether that window translates into longer survival depends on what your oncology team can do with the early warning. If an effective treatment is available and can be started sooner, earlier detection may improve outcomes. If the only option is observation, finding out months earlier that something is growing can create anxiety without a clear actionable benefit. This is a live conversation in oncology and one worth having honestly with your doctor.

How Results Are Shaping Treatment Decisions

Signatera results are increasingly being used to tailor adjuvant chemotherapy decisions, particularly in colorectal cancer. The core idea is straightforward: if you test positive for ctDNA after surgery, you probably benefit from chemotherapy; if you test negative, you might safely skip or reduce it.

Several clinical trials are testing this approach directly. The DYNAMIC-III trial randomized patients with locally advanced colon cancer to either standard treatment decisions or ctDNA-guided management, where negative patients received de-escalated therapy and positive patients received escalated therapy.¹⁶ The PEGASUS trial used a similar framework, giving ctDNA-positive patients an initial three months of combination chemotherapy and escalating to six months of a different regimen if they remained positive, while confirmed ctDNA-negative patients received a lighter regimen.¹⁷

The BESPOKE CRC data already showed that among ctDNA-positive patients, those who received adjuvant chemotherapy had roughly three times longer median disease-free survival than those who were observed without treatment.⁴ In bladder cancer, the evidence from the cystectomy setting suggests that patients with undetectable ctDNA may not benefit from adjuvant therapy, which could spare them significant side effects.⁷

A cost-effectiveness analysis modeling ctDNA-guided de-escalation in stage III colon cancer found that the standard approach of giving everyone chemotherapy was still preferred on a cost-effectiveness basis under baseline assumptions. However, the ctDNA-guided approach became cost-effective when the test’s prognostic value improved, testing costs dropped, or the benefit of chemotherapy in ctDNA-positive patients was greater.¹⁸ In other words, this is a field moving fast, and the economics are expected to shift as the evidence sharpens.

Where Signatera Fits Among Other ctDNA Tests

Signatera is not the only ctDNA-based MRD test on the market. Other platforms use a “tumor-naive” approach, meaning they look for a fixed panel of common cancer-related mutations rather than building a custom assay from your specific tumor. This fundamental design difference has practical consequences.

A small pilot study comparing Signatera (tumor-informed) with Guardant Reveal (tumor-naive) in early-stage lung cancer found overall agreement of about 73%. All three discordant cases were instances where Signatera called a positive result and Reveal did not, rather than the reverse.¹⁹ This pattern makes intuitive sense: a tumor-informed assay that knows exactly which mutations to look for should be more sensitive than a fixed panel, especially at very low ctDNA concentrations. That said, this was a tiny study, and larger comparisons are needed before drawing firm conclusions about which platform is definitively better.

This also matters for interpreting your results. If you have had testing on different platforms at different time points, the results are not directly interchangeable. A negative on one platform does not necessarily mean you would be negative on another.

Insurance Coverage and Access

Whether your insurance covers Signatera testing depends on your cancer type, stage, and insurer. Coverage policies for ctDNA tests have been inconsistent. An analysis of private payer and Medicare policies found that while ctDNA testing is increasingly recognized for certain applications, coverage remains uneven. Some guidelines endorse ctDNA testing in specific situations, such as when tissue biopsy is not feasible in lung cancer, but routine MRD monitoring after surgery has been slower to gain formal endorsement across all cancer types.²⁰ The landscape is evolving as trial data accumulates, and your oncologist’s office can often help navigate prior authorization.

The Anxiety Factor

Getting regular blood draws that can detect cancer’s return months before a scan creates a real psychological tension. Early research into the emotional experience of ctDNA monitoring found that breast cancer patients who received a ctDNA-positive result while their imaging remained clean showed a small but measurable increase in anxiety levels over six months.²¹ Living with a positive molecular result and negative imaging puts you in a gray zone where something is detected but nothing can yet be seen or treated, and that uncertainty is genuinely hard.

On the other hand, serial negative results can provide meaningful peace of mind that traditional follow-up schedules of imaging every few months cannot offer. Some patients find the more frequent data points comforting rather than stressful. How you experience ctDNA monitoring depends on your tolerance for ambiguity and how your care team communicates results. If your oncologist is ordering Signatera, it is worth discussing upfront how you want to receive and process those results, especially the scenarios where a positive result might not immediately change your treatment plan.