An interesting term is now gaining some traction in medical research -- liquid biopsy. Here's an excerpt from one of the articles that uses it (see: Genentech Scientists Zero in on “Liquid Biopsies” as a Way to Replace Tissue Biopsies in Breast Cancer):
Surgical pathologists could gain new tool to diagnose many types of cancers. It might soon be possible to determine the HER2 status of breast cancer patients from blood samples rather than tissue biopsies. If this new technology proves feasible, it would give surgical pathologists and medical laboratories a different, and possibly less complex, methodology to use when assessing a case of breast cancer. In its report about the study, Medscape Medical News, wrote that “HER2 status derived from circulating tumor cells (CTCs) from breast cancer patients was generally concordant with that derived from tumor tissue” and that “CTCs could prove to be an alternative to biopsies for assessing tumor tissue for biomarker status.” (see: Circulating Tumor Cells Are Potential Alternative to Biopsy)....The research was conducted by scientists at Genentech. As most pathologists and clinical laboratory managers know, Genentech is owned by Roche...and manufactures Herceptin, the drug used to treat breast cancer patients who are positive for the HER2 mutation. In the abstract of the presentation made at [a recent] conference, the [researchers made the following point], “Evaluation of cancer biomarkers from blood and other accessible tissues could significantly enable biomarker assessment by providing a relatively noninvasive source of representative tumor material. Circulating tumor cells (CTCs) isolated from blood of metastatic cancer patients hold significant promise in this regard.”
My first reaction to the use of the term liquid biopsy was to view it is as silly and confusing. You don't biopsy serum -- rather you collect blood and analyze the various biomarkers in the serum component. On further reflection, however, I concluded that its use may offer some benefits. It differentiates between serum biomarkers that are elaborated by circulating tumor cells (CTCs) as opposed to, say, those that are released into the blood stream from a diseased organ or solid tumor. However, it's also possible that all, or perhaps most, serum biomarkers are the result of CTCs. Here's a link to a previous note about CTCs (see: Circulating Tumor Cells for Assessing Survival in Pancreatic Cancer Patients).
CTCs can be difficult to isolate because they tend to be rare and may be released by the tumor intermittently. Biomarker assays can detect extremely small quantities of tumor protein, basically the fingerprints of CTCs. As noted above, these "liquid biopsies" are a non-invasive means to monitor the status of a malignant lesion. particularly one that is metastatic. At the very least, the use of the term may portend further integration of clinical pathology and anatomic biopsy. We seem to be ushering in an era where tumor diagnosis will be based on a mixture of lab techniques including the analysis of tissue biomarkers, serum biomarkers, and CTSs.