Natera, Inc. said its Signatera molecular residual disease test demonstrated stronger recurrence-prediction performance than Merkel cell polyomavirus antibody testing, commonly known as AMERK, in a peer-reviewed study involving patients with Merkel cell carcinoma. The head-to-head analysis found that Signatera detected 90% of clinical recurrences, compared with 55% for AMERK, while also producing a longer median warning period before recurrence became clinically evident.
The study, published online in JAMA Dermatology on July 8, 2026, evaluated 169 patients across three United States academic centres. Although Natera announced the publication on July 22, the findings represent a retrospective analysis of prospectively collected surveillance data rather than a randomized trial testing whether Signatera-guided clinical decisions improve survival.
That distinction matters. The results support Signatera as a more informative surveillance biomarker, particularly for estimating near-term recurrence risk, but they do not establish that acting on an earlier molecular signal changes treatment outcomes. The clinical opportunity lies in converting that additional warning time into more targeted imaging and risk-based follow-up without creating unnecessary procedures for patients whose positive result does not immediately reveal where recurrent disease is located.
How much stronger was Signatera than AMERK in predicting Merkel cell carcinoma recurrence?
The multicentre cohort included patients with stage I to stage IV Merkel cell carcinoma who were clinically free of disease when surveillance began. Testing was conducted between April 2020 and March 2024 at Stanford University School of Medicine, Dana-Farber Brigham and the University of Washington.
Researchers analysed 703 paired Signatera and AMERK results. The tests had to be performed within 45 days of one another, providing a closer comparison than would have been possible using unrelated samples collected at substantially different points in a patient’s surveillance journey.
The median interval between tests was 96 days, while median follow-up reached 483 days. Investigators recorded 36 clinical recurrences among 32 patients. A Signatera result was classified as positive when circulating tumour DNA was detected above zero mean tumour molecules per millilitre of plasma. A rising AMERK result required an antibody-titre increase of at least 30%.
At 365 days, Signatera had a positive predictive value of 73%, compared with 52% for AMERK. This means that a positive Signatera result was more closely associated with a clinically confirmed recurrence during the following year. The difference was statistically significant, with a reported P value of .02.
The negative predictive value at 90 days was 99% for Signatera and 97% for AMERK, with a P value of .001. While that two-percentage-point difference may appear modest, it can matter in an aggressive cancer where clinicians must decide how confidently they can interpret a negative biomarker result between imaging visits.
A positive Signatera result was associated with a 47.9-fold higher recurrence hazard than a negative result. The corresponding hazard ratio for AMERK was 7.3. The ratio between those hazard estimates was 6.6, supporting the conclusion that circulating tumour DNA provided substantially stronger prognostic separation in this cohort.
The confidence intervals were wide, however. Signatera’s hazard ratio carried a 95% confidence interval of 16.5 to 139.0, while the confidence interval for the hazard-ratio comparison extended from 2.5 to 41.0. That uncertainty reflects the limited number of recurrence events and argues against treating the precise hazard estimate as a fixed measure that will necessarily be reproduced in every clinical population.
The study also found that combining Signatera and AMERK identified only one additional recurrence compared with Signatera testing alone. That result weakens the argument for routinely ordering both tests indefinitely, although the cost, workflow and clinical consequences of a Signatera-first strategy would still need to be evaluated in implementation studies. The peer-reviewed study details are available through JAMA Dermatology.
Why does Signatera’s longer lead time matter if imaging is still required to locate recurrence?
Among patients whose recurrence was detected by both biomarkers, Signatera produced a median lead time of 5.1 months, compared with 2.1 months for AMERK. The approximately three-month difference could give clinicians additional time to intensify surveillance, repeat molecular testing or bring forward diagnostic imaging.
That lead time should not be mistaken for a demonstrated survival gain. An earlier molecular signal has clinical value only if it leads to an intervention that benefits the patient. The study did not randomize patients to Signatera-guided and conventional surveillance strategies, nor did it test whether therapy initiated solely because of circulating tumour DNA positivity improves recurrence-free or overall survival.
Imaging also remains necessary because a circulating tumour DNA result cannot identify the anatomical location or full extent of recurrent disease. A positive result may justify a more focused search, but treatment planning still depends on clinical examination, radiological confirmation, disease distribution and the patient’s previous therapy.
The high 90-day negative predictive value could be operationally important. It suggests that a negative Signatera result provides strong short-term reassurance, potentially helping clinicians calibrate imaging intensity. It does not mean a patient is free from future recurrence, particularly because the study assessed predictive value within defined time windows and Merkel cell carcinoma risk changes over time.
The most credible near-term role for Signatera is therefore as a risk-stratification layer used alongside examination and imaging. Any attempt to use a negative result to reduce imaging frequency would require prospective evidence that the approach does not delay clinically meaningful diagnoses.
Does the study prove that Signatera works universally across virus-positive and virus-negative disease?
Merkel cell carcinoma is rare but aggressive, with recurrence reported in approximately 40% of patients. AMERK measures antibodies against Merkel cell polyomavirus oncoproteins, making it useful only for the portion of patients who produce detectable antibodies.
This is an important limitation because approximately half of patients do not generate the necessary antibody signal. AMERK performance may also become more difficult to interpret following immunotherapy exposure or repeated recurrences.
Signatera takes a different approach. It uses tumour tissue and a matched normal sample to design a personalized assay that tracks mutations specific to an individual patient’s tumour. Subsequent blood samples are then analysed for circulating tumour DNA carrying that molecular signature.
The technology is not dependent on Merkel cell polyomavirus status, giving it a theoretical and previously validated advantage across virus-positive and virus-negative disease. However, the new head-to-head study required patients to have detectable polyomavirus antibodies at diagnosis because AMERK could not otherwise serve as a meaningful comparator.
The comparison therefore demonstrates Signatera’s stronger performance among antibody-producing patients. It does not directly compare the two tests in virus-negative patients because AMERK is not usable in that population. The broader claim that Signatera offers coverage across viral subtypes rests on its assay design and earlier clinical validation, not on a direct AMERK comparison involving virus-negative disease.
Natera reports that current National Comprehensive Cancer Network guidance includes circulating tumour DNA assessment for disease burden in both virus-positive and virus-negative Merkel cell carcinoma, with testing often obtained every three months. Guideline inclusion supports clinical visibility, but it does not make every testing cadence appropriate for every patient or automatically establish reimbursement.
What could prevent stronger recurrence prediction from becoming routine clinical practice?
Signatera’s personalised design creates an operational difference from conventional blood biomarkers. A suitable tumour sample must be obtained and analysed before the patient-specific assay can be built. Tissue availability, sample quality, assay-development time and coordination between pathology, oncology and the testing laboratory can therefore influence implementation.
Once the assay is established, serial surveillance requires blood collection at clinically meaningful intervals. The study’s median interval of approximately three months aligns with a practical monitoring cadence, but health systems would still need protocols governing how rapidly clinicians respond to a positive result, when testing should be repeated and when imaging should be escalated.
False-positive and false-negative results remain possible. A 73% positive predictive value at 365 days means that not every positive result was followed by a confirmed recurrence during that period. Clinicians will need to balance the opportunity for earlier detection against the anxiety, imaging burden and potential procedures that can follow an unexplained molecular signal.
The evidence also does not settle the reimbursement question. Signatera is commercially available as a laboratory-developed test performed in Natera’s Clinical Laboratory Improvement Amendments-certified laboratories, but the company states that its United States tests have not been cleared or approved by the United States Food and Drug Administration. Current Medicare coverage listed by Natera includes several solid-tumour uses, but Merkel cell carcinoma recurrence surveillance is not separately presented among the company’s principal covered indications.
A peer-reviewed comparison can strengthen future payer discussions, yet coverage decisions will also consider clinical utility, testing frequency, cost and whether molecular surveillance demonstrably changes patient management. Better prognostic accuracy is a necessary part of that case, but it is not the entire case.
Why does the Merkel cell carcinoma study matter commercially for Natera’s Signatera strategy?
Merkel cell carcinoma is unlikely to become a major standalone revenue driver because of its rarity. Its strategic value to Natera lies instead in expanding the evidence that a tumour-informed circulating tumour DNA platform can perform across multiple solid tumours and clinical settings.
Natera processed approximately 258,900 oncology tests in the first quarter of 2026, up 54.4% from approximately 167,700 a year earlier. Total first-quarter revenue increased 38.8% to $696.6 million, while the company raised its 2026 revenue outlook to between $2.74 billion and $2.82 billion. Those figures show that oncology adoption is already contributing to broader scale, although Natera still reported a first-quarter net loss of $85.1 million as operating expenses increased.
The company’s commercial challenge is to convert a growing publication base into durable ordering, guideline support and reimbursement across cancer types. The Merkel cell carcinoma study helps because it compares Signatera against an existing biomarker rather than simply demonstrating an association between circulating tumour DNA and recurrence.
Natera shares closed at $267.18 on July 21, gaining 1.7% during that session. The stock had declined approximately 2% across the preceding five trading sessions but remained about 15.5% higher over one month and roughly 91% higher over the past year. The shares were around 7% below their 52-week high of $288.04 and more than double the 52-week low of $131.81.
That performance points to broadly constructive investor sentiment around Natera’s testing growth, expanding clinical evidence and improving operating scale. It also leaves the stock carrying high expectations. The July 22 release was issued before regular United States trading, meaning the previous close cannot be interpreted as a market reaction to the Merkel cell carcinoma publication. Natera’s latest operating figures are available in its first-quarter 2026 results.
The decisive next step is not another retrospective comparison. It is prospective evidence showing how clinicians should act after a positive Signatera result and whether that response improves outcomes, reduces unnecessary imaging or delivers a defensible economic benefit. Until then, the JAMA Dermatology study gives Natera a strong argument that Signatera is the better recurrence-risk signal, while leaving the harder clinical question, what to do with that earlier signal, open.
