Although circulating tumor cells (CTCs) and cell-free DNA (cfDNA) may be “bagged” in liquid biopsy samples, they may not stay intact through all the phases of an analytical workflow. If these biomarkers suffer degradation—during storage, transportation, nucleic acid extraction, or other sample preparation steps—they may skew assays toward erroneous or equivocal results. Plainly, this is no way to investigate a patient’s cancer, make a case for an individualized therapy, or monitor attempts at correction—to say nothing of guarding against treatment resistance or cancer recurrence.
The care and handling of liquid biopsy samples is something of a chain-of-custody problem. Fortunately, various links in this chain received special attention at the International Molecular Med Tri-Con event, which was recently held in San Francisco. This Cambridge Health Institute event was not solely devoted to liquid biopsies, but it did include a channel (“Circulating Tumor Cells and Liquid Biopsy”) and a symposium (“Circulating Cell-Free DNA”) of direct relevance to our subject.
Several of the event’s presentations are summarized below. All were selected to highlight key points in the analytical workflow, from the preanalytical “securing evidence” stage to the cancer management “post-judgment modification” stage. Preanalytical processing is vital for obtaining reliable downstream test results. CTC and cfDNA assays require that liquid biopsy samples “withstand stressors of preanalytical variables introduced in clinical settings,” asserted Landon Olp, Ph.D., R&D scientist, Streck.
“Isolated CTCs can be a better sample than a tumor biopsy,” insisted Steve Crouse, chief commercial officer, Vortex Biosciences. CTCs sloughed off from multiple locations during cancer progression represent multiple cell populations from both primary and metastatic tumors, capturing cancer heterogeneity.
Tumor cells release cfDNA into the bloodstream during cell death. “But cfDNA does not exist as freely dissociated DNA,” warned Hamid Khoja, Ph.D., principal scientist, Covaris. For example, cfDNA may be bound around nucleosomes and chaperone proteins, and it must be carefully extracted for downstream analysis.
Analysis technologies such as next-generation sequencing are not without error. “The need for sensitivity and accuracy is critical,” advised Dale Yuzuki, market development director, SeraCare Life Sciences. “Without standards, people won’t know if a test and claimed sensitivity [are] real or not.”
Phillip G. Febbo, M.D., CMO, Genomic Health, added that “you have to understand the performance of your assay with respect to clinical samples and the likely allele frequencies you might see in those clinical samples.”