Type of test Blood, urine, cerebrospinal fluid (CSF)
Normal findings
No abnormal cells or cell nucleic acids
Test explanation and related physiology
The principle supporting liquid biopsy is based on repeated findings that tumors shed molecules and cells into bodily fluids (particularly blood). Since the development of molecular testing laboratory methods, researchers have shown that analyzing these molecules and cells can reveal some of the same and even additional information that tissue biopsies provide. With this additional information, personalized treatment strategies can be developed.
Tissue biopsies usually involve an invasive procedure that can be risky, costly, painful, and not easily repeated during the course of the disease therapy. Furthermore, some tumors may be inaccessible. Liquid biopsies are easily obtained through venipuncture or by obtaining a urine specimen. They can track tumors as they develop and change over time.
A liquid biopsy may be used to help find cancer at an early stage. Being able to take multiple samples of blood over time may also help doctors understand what kind of molecular changes are taking place in a tumor. Repeated liquid biopsies can be used in surveillance of treated cancer patients to look for recurrence. In a similar manner, repeated liquid biopsies during treatment can more accurately assess and monitor treatment response.
It is important, at this time, however, to recognize that liquid biopsy is far from being “standard of care.” There are many questions that must be more fully answered before this form of testing becomes clinically commonplace.
Different liquid biopsy tests analyze different kinds of tumor material, such as entire circulating free tumor cells (CTCs), circulating tumor DNA (ctDNA), RNA, proteins, and tiny vesicles of nucleic acid molecules called exomes. The tests detect these molecules or cells in various bodily fluids, including blood, urine, CSF, and saliva.
Liquid biopsies are now being used in lung, colo-rectal, esophageal, gastric, hepatic, pancreatic, head and neck, ovarian, myeloma, lymphoid, and breast cancers. In cardiology, endothelial cells identified in the blood, may indicate myocardial infarction (MI). Cell free fetal DNA (see cell-free maternal testing) is used to identify serious fetal genetic and chromosomal abnormalities.
Procedure and patient care
• See inside front cover for Routine Blood Testing.
• Fasting: no
• Blood tube commonly used: see laboratory for directions
Abnormal findings
- Presence of circulating tumor cells
- Presence of DNA or RNA fragments of known tumor cells
