Circulating tumor cells: from bench to bedside

Abstract

Circulating tumor cells (CTCs) represent a surrogate biomarker of hematogenous metastases. In recent years, their detection has gained increasing interest. There is ample evidence regarding the ability to detect CTCs and their prognostic relevance, but their demonstrated predictive value in therapeutic response monitoring is clinically even more meaningful. Many clinical trials in the early and metastatic cancer setting now include CTCs as a monitoring parameter, and numerous translational studies attempting their molecular characterization are under way. There has been great progress in defining the clinical importance of CTCs, and it now seems likely that we may expect wider implementation of CTCs as a diagnostic oncology tool to monitor therapeutic response in real time. Novel technologies may further facilitate molecular characterization of CTCs and development of novel therapeutic targets, possibly leading to more powerful treatment strategies for cancer patients. As the detection and evaluation of CTCs are becoming an increasingly important diagnostic and prognostic tool, the goal of this review is to communicate the knowledge obtained through analysis of primary tumors and CTCs to oncologists and medical specialists in managing patients with cancer.

Figure 1

Capture and immunofluorescent (IF) staining of CTCs by the microfilter device in model systems. Following filtration, microfilters are stained with a CK cocktail conjugated to Alexa Fluor 488 secondary fluorescent antibody (green), CD45 conjugated to Alexa Fluor 594 secondary fluorescent antibody (red), and DAPI (blue) for nuclear visualization. CTCs are identified as nucleated, CK⁺/CD45⁻ cells with morphologic criteria consistent with malignancy. (a) Positive control cytospin preparation where MCF-7 breast cancer cells were mixed with nontumor blood cells from a healthy donor. Note the difference in size between CK⁺/CD45⁻ tumor cells and CK⁻/CD45⁺ nontumor peripheral blood mononuclear cells. (b) T47D breast cancer cells were mixed with phosphate buffer saline, captured by the microfilter device, and identified by CK/CD45 IF staining using confocal microscopy.

Figure 2

CTC/immune cell clusters captured by the microfilter device in clinical blood samples. Representative image from a metastatic prostate cancer blood sample demonstrating a CTC/immune cell cluster, where CK⁻/CD45⁻ cells directly associated in the cluster are indicated with arrows.