Use of Circulating Tumor DNA for Cancer Immunotherapy.

Liquid biopsy offers a versatile, noninvasive opportunity to diagnose, characterize, and monitor disease in patients with cancer. There are particularly promising applications with which to use liquid biopsies to predict and evaluate response to immunotherapy. Circulating tumor DNA (ctDNA) can reflect the genomic state of a patient's overall disease and, thus, might identify prognostic and predictive biomarkers for immune checkpoint inhibitor therapy. ctDNA might also be a proxy for a patient's overall disease burden, which could be used for early diagnosis and monitoring treatment response. These applications can enable novel trial designs, such as enrollment of early-stage patients with a high risk for relapse, and the evaluation of response patterns unique to immunotherapies. However, barriers to the widespread adoption of ctDNA assessment remain, including the absence of standardized procedures for collecting and processing ctDNA samples and relatively limited data on clinical utility. Identifying and solving these challenges could allow ctDNA to become a powerful clinical and research tool in the era of personalized immunotherapy.