Detecting liquid remnants of solid tumors treated with curative intent: Circulating tumor DNA as a biomarker of minimal residual disease (Review).

Circulating tumor DNA (ctDNA) has emerged as a promising biomarker of minimal residual disease (MRD) in solid tumors. There is increasing evidence to suggest that the detection of ctDNA following curative‑intent treatments has high potential in anticipating future relapse in various solid tumors. Multiple liquid biopsy technical approaches and commercial platforms, including tumor‑informed and tumor‑agnostic ctDNA assays, have been developed for ctDNA‑based MRD detection in solid tumors. Accurate ctDNA‑based MRD analysis remains a critical technical challenge due to the very low concentration of ctDNA in peripheral blood samples, particularly in cancer patients following a curative‑intent surgery or treatment. The present review summarizes the current key technical approaches that can be used to analyze ctDNA in the surveillance of MRD in solid tumors and provides a brief update on current commercial assays or platforms available for ctDNA‑based MRD detection. The available evidence to date supporting ctDNA as a biomarker for detection of MRD in various types of solid tumors is also reviewed. In addition, technical and biological variables and considerations in pre‑analytical and analytical steps associated with ctDNA‑based MRD detection are discussed.