FDA Clears Test for Monitoring Metastatic Colorectal Cancer

The US Food and Drug Administration (FDA) has granted an expanded clearance for the CellSearch System to be used as an aid in the monitoring of metastatic colorectal cancer. CellSearch is currently approved for monitoring metastatic breast cancer.

The CellSearch System identifies and counts circulating tumor cells (CTCs) in a blood sample to predict progression-free survival and overall survival in patients with metastatic colorectal or breast cancer, and can do so earlier than the current standard of care. The results of serial testing for CTCs with the CellSearch System, in conjunction with other clinical methods for monitoring, can help physicians assess disease progression, thereby guiding more informed care decisions earlier.

The CellSearch System is the first diagnostic test to automate the detection and enumeration of CTCs, cancer cells that detach from solid tumors and enter the blood stream, and is the standard in a new class of diagnostic tools. The system's specificity, sensitivity, and reproducibility allow for serial assessment of CTCs as early as the first cycle of treatment to help evaluate disease progression sooner.

Key Trial

A prospective, multicenter clinical trial was conducted to validate the expanded clearance for CellSearch. The study, which took place in 55 clinical centers in the United States and Europe, involved 430 metastatic colorectal patients about to enter first- or second-line therapy. Data showed that patients with less than three CTCs at baseline had significantly better survival rates vs patients with more than three CTCs—an overall finding consistent with metastatic breast cancer patients. Data also showed that CTCs are a strong independent predictor of progression-free survival and overall survival, and that the combination of CTC analysis and radiologic assessment may provide the most accurate assessment of prognosis.

The CellSearch test works by using antibodies that are joined to microscopic iron particles, called ferrofluid. These antibody/ferrofluid combinations attach very specifically to CTCs. Powerful magnets then "pull" the CTCs out of the blood sample. They are then stained with additional biomolecules and chemicals so that they can be positively identified as CTCs. The CellSearch test differs from the current standard of care because it can be used much earlier than traditional imaging (eg, CT scans), and is not subject to the variation observed with other serum tumor markers.