Signatera is a personalized blood test that detects tiny fragments of tumor DNA circulating in your bloodstream after cancer surgery. Its primary purpose is to answer a question that imaging scans often can’t: is there any cancer still left in your body? The test is custom-built for each patient using their own tumor’s genetic fingerprint, which makes it different from standard blood tests or generic liquid biopsies.
How the Test Works
Signatera starts with a tissue sample from your tumor, typically collected during surgery. A lab sequences the full set of genes in that tissue along with a normal blood sample, then identifies up to 16 mutations unique to your specific cancer. These mutations become your personalized panel, a custom-built detection tool designed to find only your tumor’s DNA in future blood draws.
Once that panel is ready, monitoring is straightforward. You give a blood sample (two specialized collection tubes, plus one standard tube for first-time patients), and the lab searches your plasma for those 16 specific mutations. If two or more of your tumor-specific mutations show up, the result is positive, meaning tumor DNA is circulating in your blood. The amount is reported as tumor molecules per milliliter of plasma, giving your oncologist both a yes-or-no answer and a sense of how much tumor DNA is present.
The test can detect tumor DNA at extremely low concentrations, down to 0.01% of the DNA in your blood. That’s a level far below what imaging can pick up, which is why the test is useful for catching cancer that’s still too small to see on a CT scan or MRI.
What the Test Is Used For
Signatera serves three main roles in cancer care: detecting minimal residual disease after surgery, monitoring for recurrence over time, and helping guide treatment decisions.
Minimal residual disease, or MRD, refers to small amounts of cancer that remain after surgery but aren’t visible on scans. Finding out whether MRD is present matters because it changes the risk picture dramatically. In a pooled analysis of three colorectal cancer studies, patients who tested positive for tumor DNA after surgery had a five-year recurrence-free survival rate of just 38.6%, compared to 85.5% for those who tested negative. That translates to roughly a seven-fold higher risk of recurrence for patients with detectable tumor DNA.
For recurrence monitoring, the test can flag cancer’s return well before symptoms appear or scans detect anything. Depending on the cancer type, Signatera has identified recurrence a median of 2.3 to 10.1 months ahead of standard imaging. That lead time can open a window for earlier treatment.
Which Cancers It Covers
Signatera has been studied and used across several solid tumor types. Colorectal cancer has the deepest evidence base, and Medicare has established billing pathways specifically for colorectal cancer testing. Beyond that, the test has been evaluated in breast cancer, non-small cell lung cancer, melanoma, renal cell carcinoma, and bladder cancer. Clinical trials are actively using it in several of these cancers to determine whether treatment decisions guided by the test lead to better outcomes.
Accuracy and Detection Limits
In colorectal cancer studies, Signatera has shown 88% sensitivity and 98% specificity for detecting minimal residual disease. In practical terms, the 98% specificity means false positives are rare. If the test says tumor DNA is present, it very likely is. The 88% sensitivity means a small number of patients with residual disease will get a negative result, so a single negative test doesn’t guarantee cancer is completely gone, which is one reason oncologists use serial testing over time rather than relying on a single draw.
How Results Guide Treatment Decisions
One of the most promising applications is using Signatera results to determine who actually benefits from additional treatment after surgery. In a bladder cancer trial, 37% of patients had detectable tumor DNA about 11 weeks after surgery. Among those positive patients, immunotherapy cut the risk of death by 41% compared to observation alone. But patients who tested negative got no measurable benefit from the same immunotherapy. That pattern suggests the test could help spare some patients from unnecessary treatment while identifying those who need it most.
Several ongoing clinical trials are testing this approach in breast cancer as well, randomizing patients who test positive to either additional targeted therapy or standard care. In lung cancer, researchers have observed that rising tumor DNA levels during chemotherapy can signal drug resistance, while declining levels after treatment correlate with favorable outcomes.
Where Guidelines Stand Today
Despite strong prognostic data, major oncology guidelines haven’t yet endorsed routine use of the test to guide treatment decisions outside of clinical trials. The National Comprehensive Cancer Network has noted that current data are insufficient to recommend ctDNA testing as the basis for starting or stopping chemotherapy in resectable colon cancer. Their position is that using the test for prognosis or surveillance should involve shared decision-making between patient and provider, rather than being treated as standard protocol.
The core issue isn’t whether the test works for detection. It clearly does. The gap is in proving that acting on results, changing treatment based on a positive or negative test, consistently leads to better survival. Large randomized trials designed to answer that question are underway but haven’t yet reported mature results for most cancer types.
Insurance Coverage
Medicare has established coverage pathways for Signatera in colorectal cancer, with specific billing codes and diagnostic requirements tied to malignancies of the colon, rectum, and anal canal. Coverage for other cancer types through Medicare is less clearly defined. Private insurance reimbursement varies by carrier and plan, and coverage decisions often depend on the specific cancer type and clinical context. If your oncologist recommends the test, it’s worth confirming coverage with your insurer before the blood draw, particularly if it’s being ordered for a cancer type outside the colorectal category.
What to Expect as a Patient
The first step requires your oncologist to send a tumor tissue sample (usually from your original surgery) along with a blood draw to build your personalized panel. This initial setup takes longer than subsequent monitoring tests because the lab needs to sequence your tumor and design your custom assay. After that, each monitoring round is just a blood draw. The collection itself takes minutes and uses a kit provided by the test manufacturer.
Your oncologist will determine how often you’re tested based on your cancer type, stage, and treatment timeline. Some patients are tested every three to six months during the first few years after surgery, when recurrence risk is highest. Each follow-up result tells your care team whether tumor DNA is detectable, undetectable, or trending in a particular direction, information that adds a layer of precision to the standard follow-up schedule of scans and physical exams.