US Food and Drug Administration (FDA) has granted an expanded clearance for Veridex LLC's CellSearch System to be used as an aid in the monitoring of metastatic prostate cancer (MPC) patients. The CellSearch System currently is cleared for monitoring metastatic breast and metastatic colorectal cancer patients.
The CellSearch System identifies and counts circulating tumour cells (CTCs) in a blood sample to predict progression-free survival and overall survival in patients with metastatic breast, colorectal or prostate cancer, and can do so earlier than the current standard of care. The results of serial testing for CTCs with the CellSearch System provide additional information to the oncologist and does so earlier than other currently approved diagnostic modalities, thereby allowing the oncologist to make more-informed patient care decisions.
According to the American Cancer Society, prostate cancer claims approximately 27,000 lives each year, the vast majority of which are a result of recurrent metastatic disease. Metastatic prostate cancer occurs when tumour cells spread to other locations in the body and grow. Currently, oncologists often have to wait several months before they can determine if a specific treatment is beneficial to the patient. The CellSearch System helps physicians to predict disease progression and patient survival any time during therapy.
"I am extremely pleased that we now can offer this test to patients with metastatic prostate cancer," said Dr. Louis Fink of the Nevada Cancer Institute in Las Vegas, Nevada. "We have been evaluating the clinical utility of the CellSearch System in patients with metastatic prostate cancer since January 2007. Our findings demonstrate a strong indication that the baseline number of Circulating Tumour Cells (CTCs) is prognostic, and that the number of prostate CTCs is altered by the therapy." Dr. Nick Vogelzang, also of the Nevada Cancer Institute, continued, "We have compared CellSearch CTC test results to the standard clinical and biomedical parameters, such as prostate specific antigen (PSA) measured in MPC patients. A decrease in the number of CTCs is most often associated with patients successfully responding to therapy. Further analysis of CTCs may provide information as to the most efficacious treatments for specific individuals." These data will be presented at the 2008 American Association of Cancer Research (AACR) annual meeting in San Diego on April 12-16, 2008, the company said.
The CellSearch System is the first diagnostic test to automate the detection and enumeration of CTCs, cancer cells that detach from solid tumours and enter the blood stream, and is 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.
The CellSearch System was originally cleared by the FDA in January 2004 as a diagnostic tool for identifying and counting CTCs in a blood sample to predict progression-free survival and overall survival in patients with metastatic breast cancer. In November 2007, the CellSearch System was cleared as an aid in monitoring metastatic colorectal patients.
A prospective, multi-centre clinical trial was conducted to validate the expanded clearance for CellSearch. The study, which took place in 65 clinical centres in the United States and Europe, involved 231 metastatic prostate cancer patients about to enter first- or later-line chemotherapy. Data showed that patients with less than five CTCs at baseline had significantly better survival rates versus patients with more than five CTCs. 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 prostate specific antigen (PSA) assessment may provide the most accurate assessment of prognosis.
"Continued clinical studies validate the significance of circulating tumour cells, and now extend that significance to patients with metastatic prostate cancer," said Robert McCormack, vice president, Medical and Scientific Affairs, Veridex. "Elevated CTCs in the blood stream are associated with shorter progression-free and overall survival rates."
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 and they are then stained with additional bio-molecules and chemicals so that they can be positively identified as CTCs. The CellSearch test differs from the current standard of care because it can accurately predict prognosis much earlier than the prostate specific antigen serum tumour marker test.
In August 2004, a clinical study using the CellSearch test in metastatic breast cancer patients was published in The New England Journal of Medicine. The authors of this study concluded: "The very short median progression-free survival in patients with elevated circulating tumour cells at the first follow-up visit suggests that these patients are receiving ineffective therapy." In addition, as recently as November 2006, a metastatic breast cancer study was published in Clinical Cancer Research where the authors concluded: "The results reported here indicate that the evaluation of CTCs is an accurate measure of treatment efficacy. The ability to serially quantitate and interrogate CTCs in patients with breast cancer makes possible new ways of managing and investigating the disease."