RaDaR is a personalized blood test that looks for tiny amounts of circulating tumor DNA (ctDNA) after a cancer has been treated or while it is being monitored. Its main purpose is molecular residual disease (MRD) detection: finding tumor-derived DNA that may remain when scans show no visible cancer. The current RaDaR ST assay uses DNA from a patient’s tumor to build an individualized panel, then checks later blood samples for those same tumor-specific changes. A positive result can signal a substantially higher risk of recurrence, sometimes months before a recurrence becomes visible on imaging. A negative result is reassuring but does not prove that every cancer cell is gone, because some tumors release very little DNA into the bloodstream. RaDaR is therefore best understood as one piece of cancer surveillance, interpreted with the cancer type, treatment history, imaging, pathology, symptoms, and the timing of each blood draw.
- What RaDaR measures: Patient-specific tumor DNA fragments circulating in plasma, rather than a general tumor-marker level.
- Positive result: ctDNA was detected and usually indicates molecular evidence of residual or recurrent cancer and a higher recurrence risk.
- Negative result: No ctDNA was detected at that blood draw, but microscopic disease can still be present below the assay’s detection limit.
- How the test is built: Tumor tissue is sequenced first; the current RaDaR ST workflow can track up to 48 patient-specific somatic mutations.
- Why serial testing matters: Repeated blood draws can reveal a new positive result or changing ctDNA pattern that a single time point could miss.
Table of Contents
- What the RaDaR test is and what it measures
- How RaDaR tumor-informed testing works
- When RaDaR may be used in cancer care
- How to interpret positive and negative RaDaR results
- Accuracy, sensitivity, and important limitations
- RaDaR compared with other ctDNA and surveillance tests
- What to discuss with your oncology team after a result
What the RaDaR test is and what it measures
RaDaR is a tumor-informed ctDNA assay. “Tumor-informed” means the laboratory first studies DNA from the patient’s own tumor and identifies mutations that can serve as a molecular fingerprint. The blood test then searches for that fingerprint in cell-free DNA circulating in plasma.
This is different from a broad ctDNA mutation panel that scans a fixed list of cancer genes to find treatment targets. RaDaR is primarily designed to answer a narrower question: Can tumor-specific DNA still be detected, or has it reappeared, after treatment?
The current NeoGenomics RaDaR ST test uses whole-exome sequencing (WES) of tumor tissue to establish the tumor’s genetic profile. It can then track up to 48 patient-specific somatic mutations. Somatic mutations are DNA changes acquired by the tumor; they are not the same as inherited genetic variants passed through families.
The clinical concept behind RaDaR is ctDNA molecular residual disease testing. After surgery, radiation, systemic therapy, or another treatment given with curative intent, the remaining amount of cancer may be far too small for CT, MRI, or PET scans to show. If residual tumor cells release DNA into the bloodstream, a sensitive assay may detect that molecular signal.
MRD in solid tumors is not a measured mass. A positive blood test does not say that a lesion is a certain size, and a negative result does not establish a “zero cancer cells” state. It is better viewed as a highly specific molecular signal whose meaning depends on the assay, cancer type, treatment setting, and collection time.
How RaDaR tumor-informed testing works
RaDaR requires an initial setup phase before routine blood-only monitoring can begin.
- Tumor tissue is obtained. This is usually archived tissue from a biopsy or surgery. Adequate tumor content and tissue quantity are needed for genomic analysis.
- The tumor is sequenced. Whole-exome sequencing identifies many DNA variants across the tumor.
- Patient-specific targets are selected. A personalized panel is created from somatic variants that are suitable for reliable tracking.
- Blood is analyzed. Plasma cell-free DNA is tested with multiplex PCR and next-generation sequencing (NGS) for the selected tumor-specific variants.
- Later blood draws reuse the personalized assay. Once the assay is established, follow-up testing generally requires blood rather than new tumor tissue.
The current RaDaR ST specimen instructions call for tumor tissue plus two 10 mL Streck cell-free DNA blood tubes at the first time point, followed by two 10 mL blood tubes at later time points. NeoGenomics lists a longer turnaround for the first personalized time point than for follow-up tests because assay development must occur first.
The personalized approach has an important analytical advantage. Instead of searching the entire genome for a weak cancer signal, the laboratory knows exactly which mutations to look for. Tracking multiple variants also makes the call more robust than relying on one mutation that could be absent from a particular plasma sample.
That multi-target design also helps at very low tumor fractions, where only a few cancer-derived molecules may be present in the tube. The assay can combine evidence across several patient-specific loci rather than requiring one mutation to carry the entire signal. This does not eliminate sampling error, but it is one reason personalized MRD assays can operate at concentrations far below those used for ordinary broad plasma genotyping.
RaDaR workflows also use a blood-cell control to help remove signals from clonal hematopoiesis, an age-related process in which normal blood-forming cells acquire mutations. Clonal hematopoiesis can mimic a tumor mutation in plasma and is one reason careful filtering matters in cell-free DNA cancer testing.
The result is still constrained by biology. A laboratory cannot detect tumor DNA that never enters the sampled blood, and a 20 mL blood draw captures only a small fraction of the body’s circulating DNA at one moment.
When RaDaR may be used in cancer care
RaDaR is most relevant when the clinical question involves residual disease, recurrence risk, or longitudinal monitoring, rather than initial cancer diagnosis.
Common use cases include:
- checking for ctDNA after curative-intent surgery or other definitive treatment;
- monitoring during surveillance for a new molecular signal;
- assessing ctDNA changes during systemic therapy in selected settings;
- adding molecular risk information when standard tests leave uncertainty.
The evidence base is cancer-specific. In early-stage non-small cell lung cancer, a 2022 study using patient-specific RaDaR assays found that post-treatment ctDNA detection was strongly associated with worse recurrence-free survival and could precede clinical recurrence by a median of about 213 days. In a 2022 study of high-risk hormone receptor-positive/HER2-negative breast cancer more than five years after diagnosis, ctDNA was detected before all observed distant metastatic recurrences, with a median lead time of 12.4 months. A 2025 breast cancer study using the RaDaR approach also showed that postoperative or follow-up ctDNA detection was strongly associated with recurrence.
These numbers are useful examples, not universal promises. Lead time can vary substantially by tumor type, disease location, blood-draw schedule, imaging schedule, treatment, and assay sensitivity.
Cancer location matters as well. Some small tumors and certain metastatic sites—especially disease confined to the brain or other low-shedding sites—may release little ctDNA into peripheral blood. A circulating tumor DNA test therefore cannot replace anatomy-based surveillance when imaging or examination is standard for that cancer.
Current professional guidance also emphasizes actionability. ASCO’s 2026 ctDNA guideline states that ctDNA testing beyond tumor-genetic alteration testing may be offered when there is a specific evidence-based action that can be taken from the result, or when the result can resolve ambiguity with standard assessment. This is particularly important in MRD because a molecular positive result can appear before a lesion can be localized.
How to interpret positive and negative RaDaR results
A RaDaR result is usually most useful as a detected/not detected molecular status interpreted over time.
| Result pattern | What it generally means | What it does not prove |
|---|---|---|
| Positive after definitive treatment | Tumor-specific ctDNA is detectable; recurrence risk is usually substantially higher than in ctDNA-negative patients. | It does not show where recurrence is located or guarantee that imaging is already positive. |
| Negative after definitive treatment | No tracked tumor-specific ctDNA was detected in that sample; this is generally a favorable sign. | It does not prove cure or exclude microscopic disease below the detection limit. |
| Negative then later positive | A new molecular signal may indicate emerging recurrence or progression and deserves clinical review. | It does not by itself identify a lesion or determine the correct treatment. |
| Positive then negative during therapy | ctDNA clearance may be consistent with molecular response. | It does not guarantee durable remission or replace other response assessments. |
What a positive result means
A positive RaDaR result means the assay detected enough evidence from the patient-specific mutation set to classify ctDNA as present. In post-treatment MRD studies, this has repeatedly correlated with a high risk of later clinical recurrence.
The most important next question is not simply “How high is it?” but “What evidence-based decision should this result change in my specific cancer?” Depending on the disease and treatment setting, the oncology team may consider earlier imaging, a different imaging modality, closer follow-up, additional systemic therapy when supported by evidence, or a clinical trial designed around ctDNA-positive MRD.
A positive result can be emotionally difficult because it may identify molecular recurrence before conventional tests can show where the cancer is. That gap is a known feature of highly sensitive MRD monitoring, not necessarily a contradiction between the blood test and imaging.
What a negative result means
A negative result means the selected tumor-specific variants were not detected above the assay’s calling threshold in that sample. It lowers concern compared with a positive result, especially when results remain negative on serial testing.
However, negative does not mean “cancer-free with certainty.” False-negative results can occur when the remaining tumor burden is extremely small, the tumor sheds little DNA, the disease is in a low-shedding site, treatment suppresses DNA release, or the blood sample contains too few informative molecules.
Serial negative tests can provide more confidence than one isolated negative result, but they still need to be interpreted alongside routine follow-up.
Accuracy, sensitivity, and important limitations
RaDaR was designed for very low ctDNA levels. Current NeoGenomics materials describe the assay as tracking up to 48 variants and report an analytical limit of detection in the low parts-per-million range under defined conditions. Older and current clinical studies have detected samples with estimated variant allele fractions below 0.01%, illustrating why deep, personalized testing can matter in MRD.
Analytical sensitivity is not the same as clinical sensitivity. An assay can reliably detect a DNA signal when it is present in a test tube, yet still miss a clinical recurrence because the tumor did not release enough DNA into the blood sample.
Several limitations deserve attention:
- Tissue is required to build the assay. If archived tumor material is unavailable or inadequate, the personalized test may not be possible.
- The first result takes longer. Tumor sequencing and custom assay development add time before the initial MRD result.
- Biology affects shedding. Stage, tumor type, lesion size, vascularity, metastatic site, and recent treatment can all change ctDNA release.
- A positive result does not localize disease. Imaging and clinical evaluation remain necessary.
- A negative result does not rule out recurrence. Even a highly sensitive assay samples a finite amount of blood.
- Clinical utility is still evolving. Strong prognostic evidence does not automatically prove that changing treatment because of a positive test improves survival.
The last point is crucial. MRD tests can identify risk very effectively, but prognostic value and treatment-guiding value are different questions. A marker is prognostic if it predicts who is more likely to relapse. It is clinically predictive only when evidence shows that a particular action based on the marker improves outcomes or safely avoids unnecessary treatment.
For that reason, ctDNA-directed treatment strategies are increasingly being tested in prospective and randomized trials. The appropriate action after a RaDaR result can differ substantially between cancers.
RaDaR compared with other ctDNA and surveillance tests
RaDaR belongs to the tumor-informed MRD category, so its closest comparison is another tumor-informed ctDNA test, such as Signatera, rather than a general genomic liquid biopsy.
| Test type | Main purpose | Needs tumor tissue? | Key limitation |
|---|---|---|---|
| RaDaR | Personalized ctDNA MRD and recurrence monitoring | Yes, for initial assay design | Cannot detect disease that is not shedding enough tracked ctDNA |
| Tumor-naive MRD assay | MRD detection using a fixed or tissue-free molecular approach | No | Performance varies by platform; some fixed-panel approaches may be less sensitive at very low disease burden |
| Broad liquid-biopsy genomic panel | Find actionable mutations and resistance mechanisms | Usually no | A negative result may reflect low tumor fraction rather than absence of the mutation |
| CT/MRI/PET imaging | Locate and measure anatomic or metabolic disease | No | May not detect microscopic residual disease |
| Traditional serum tumor marker | Track a protein marker when useful for a specific cancer | No | Can be nonspecific and is not available or reliable for every tumor |
A tumor-naive ctDNA test can start without personalized tumor sequencing, which can be valuable when tissue is unavailable or speed matters. Tumor-informed methods, by contrast, gain specificity and potentially sensitivity by concentrating sequencing effort on the individual tumor’s known variants.
RaDaR also should not be confused with tests designed to find a targetable mutation such as EGFR, ESR1, or KRAS. Those assays answer what mutation is present; MRD assays mainly answer whether a known tumor signal is detectable now.
What to discuss with your oncology team after a result
A RaDaR result is most useful when it is connected to a defined clinical plan. Useful questions include:
- What was the purpose of testing at this time point—post-treatment MRD, surveillance, or treatment-response monitoring?
- Is this use of RaDaR validated for my cancer type and stage?
- If the result is positive, what action is supported by evidence: imaging, closer surveillance, treatment, or a clinical trial?
- If imaging is negative but ctDNA is positive, when and how will imaging be repeated?
- If the result is negative, does my standard imaging or examination schedule change?
- How often should ctDNA be repeated, and what pattern would be considered meaningful?
- Could my cancer’s location or biology make a false-negative result more likely?
- Is the original tumor tissue adequate for the personalized assay, or is additional tissue needed?
Timing deserves specific discussion. Blood obtained immediately after major surgery can contain abundant non-tumor cell-free DNA from tissue injury, which can dilute the tumor signal. Studies use defined post-treatment landmark windows, and a test ordered outside the validated timing for that cancer may have a different meaning.
No ctDNA test should delay evaluation of new symptoms. New pain, neurologic symptoms, shortness of breath, unexplained weight loss, bleeding, a new mass, or other concerning changes need clinical assessment even if the most recent MRD test was negative.
RaDaR can add a highly sensitive molecular layer to surveillance, but the strongest interpretation comes from combining the ctDNA trend with pathology, stage, treatment history, imaging, physical examination, and the evidence available for that specific cancer.
References
- Circulating Tumor DNA Testing in Solid Tumors and Lymphoma: ASCO Guideline 2026 (Guideline)
- RaDaR® ST | NeoGenomics Laboratories 2026 (Official Test Information)
- Pan-Cancer Pre-Treatment ctDNA Detection Using a Highly Sensitive Tumor-Informed Assay. 2026
- Longitudinal evaluation of circulating tumor DNA in patients undergoing neoadjuvant therapy for early breast cancer using a tumor-informed assay 2025
- Residual ctDNA after treatment predicts early relapse in patients with early-stage non-small cell lung cancer 2022
- Circulating Tumor DNA and Late Recurrence in High-Risk Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative Breast Cancer 2022
Disclaimer
This article is for general educational purposes and does not replace advice from your oncology team. The meaning and appropriate use of RaDaR depend on cancer type, stage, treatment, test timing, and the clinical evidence for that setting. Do not start, stop, or change cancer treatment based on a ctDNA result without discussing it with the treating clinician.
