A Signatera positive result indicates the presence of circulating tumor DNA (ctDNA) in your patient’s blood and by extension, the presence of tumor in the patient’s body. Positive results are highly correlated with inferior prognosis (e.g. reduced disease-free survival). The numerical value is associated with overall tumor burden for each patient, but only on a relative basis compared to previous Signatera results. In other words, the significance is in the trend; is the amount of ctDNA detected increasing, decreasing, stable from one time point to another. We have not proven that a certain quantity of ctDNA detected equates to a certain outcome, prognosis, tumor-burden or disease state; this likely varies from person to person. However, increases in MTM/mL for a given patient are associated with an increase in tumor burden for that patient and visa versa.
A negative result indicates that ctDNA was not detected in your patient’s blood at a given timepoint. This does not mean that the patient is in remission (absence of cancer that has been treated), rather it could mean that the tumor burden that remains is at such low levels that it is not detected in the blood. For this reason, Signatera is best utilized when ordered repetitively, so that ctDNA detection and/or ctDNA levels can be assessed in a longitudinal manner. The longer the patient remains ctDNA negative, the more likely that individual will not relapse.