As noted by the College of American Pathologists:
The advent of "precision" medicine has been characterized by improvements in diagnostic, prognostic, and therapeutic approaches. The “liquid biopsy” has recently and rapidly emerged as a method to minimize the amount of tissue needed for testing, as a less invasive and safer alternative to more traditional procedures. While definitions vary on the precise meaning of this term, it can broadly be thought of as collection of a body fluid sample to test for relevant biomarkers to inform patient management. A “liquid biopsy” does not replace a tissue-based diagnosis, but rather provides alternate sampling for (typically) molecular testing purposes.
Source: Olson, Damon R, The 'Liquid' Biopsy,
College of American Pathologists 22 Mar 2022