CellSearch represents a significant advancement in cancer diagnostics, functioning as a liquid biopsy. This technology focuses on detecting and counting circulating tumor cells (CTCs) found in a patient’s bloodstream. These rare cells, shed from primary tumors, offer a non-invasive way to gain insights into a cancer’s behavior and progression. The information provided by CellSearch complements traditional diagnostic methods, offering a more complete picture of a patient’s disease status.
How CellSearch Identifies Cancer Cells
The CellSearch System isolates and identifies circulating tumor cells from a blood sample. First, a blood sample, typically 7.5 mL, is collected and processed to separate blood components. Magnetic beads, coated with antibodies targeting EpCAM (epithelial cell adhesion molecule), are then introduced. EpCAM is a protein commonly found on the surface of many epithelial-derived cancer cells, allowing for their capture.
Once EpCAM-targeted magnetic beads bind to CTCs, a magnetic field pulls these cells away from other blood cells. The isolated cells are then stained with fluorescent markers. Fluorescent anti-cytokeratin antibodies identify the epithelial origin, while a fluorescent anti-CD45 antibody excludes white blood cells. A DNA stain, DAPI, highlights cell nuclei. Finally, an automated analysis system scans the sample, identifying and enumerating cells that meet the specific criteria for CTCs (EpCAM-positive, cytokeratin-positive, DAPI-positive, and CD45-negative).
CellSearch’s Use in Cancer Care
CellSearch plays a role in managing cancer by providing insights into disease progression and treatment response. This liquid biopsy monitors changes in a patient’s cancer over time without repeated tissue biopsies. Tracking circulating tumor cells provides a real-time snapshot of the disease, useful for understanding how a tumor responds to therapy.
A decrease in CTCs after treatment may suggest effective therapy, while an increase could indicate treatment resistance or disease progression. CellSearch is used in the management of metastatic cancers, including breast, prostate, and colorectal cancers. It aids in assessing patient prognosis and can help predict progression-free survival and overall survival. This continuous monitoring helps clinicians adjust treatment strategies for more personalized and effective care.
Understanding CellSearch Results
The primary outcome of a CellSearch test is a “CTC count,” representing the number of circulating tumor cells detected in a standard blood sample. This count provides important prognostic information for patients with certain metastatic cancers. For example, in metastatic breast and prostate cancers, a count of five or more CTCs per 7.5 mL of blood indicates an unfavorable prognosis, correlating with shorter progression-free survival and overall survival. For metastatic colorectal cancer, a cutoff of three or more CTCs per 7.5 mL defines an unfavorable prognosis.
Changes in CTC numbers over time carry significant clinical meaning. A decrease in the CTC count after initiating new treatment indicates a positive response, suggesting the treatment effectively reduces tumor burden. Conversely, a persistent or increasing CTC count despite treatment may signal the therapy is not working, prompting clinicians to consider alternative strategies. CellSearch results are interpreted alongside other clinical information, such as imaging scans, traditional blood tests, and a patient’s overall medical history, to guide treatment decisions and provide comprehensive cancer care. The CellSearch System was the first technology to receive FDA clearance for CTC enumeration in metastatic breast, colorectal, and prostate cancers, highlighting its clinical utility.