I'm a retired biopharma & diagnostics medical director. I worked on the development & validation of a number of ctDNA/cfDNA assays that are used to monitor patients' responses to therapies and minimal residual disease burden. The Signatera assay, developed by Natera, and offered by FoundationOne, has very good clinical specificity, sensitivity and prognostic significance.. The assay relies upon the acquisition and construction of a patient's unique molecular genetic profiles from the DNA obtained from a tumor or lymph node. A patient' blood samples is then screened for the presence of cell tumor DNA fragments (ctDNA). It may detect new clonal .mutations as well. A high ctDNA score is indicative of recurrent/residual disease and potentiall a worse prognosisis. Your oncology team can use the information provided by the assay to adjust/modify/ change your therapeutic regimens to hopefully slow the progress of your disease.
There are a number of similar, if not superior offerings to Signatera from other clinical labs such as Quest's recently launched,Haystack MRD test, Guardant 360 MRD test, Circulogene's ctDNA/RNA test among others. All of these assays have minor variations in their respective sample prep, analyses and reporting of results. All appear to offer similar levels of sensitivity, specificity and prognostic significance as well as similar pricing. Their respective turn around times for reporting test results is variable, but is usually ~2 weeks.