Various news media outlets have trumpeted a new blood test that detects cancer cells, even though the diagnostic tool still remains in the infant stages of clinical application. Partnering with a Boston-based start-up company, health care giant Johnson & Johnson announced yesterday that it will work through its Veridex and Ortho Biotech Oncology units to bring the product to market. The test’s proponents claim that it is sensitive enough to detect even one cancer cell among a billion normal cells.
Though he believes the test is a novel diagnostic tool, ACSH's Dr. Gilbert Ross says that the test's development is very preliminary and that it requires further clinical studies to determine its predictive power. One application of the test detected cancer cells in the blood of two-thirds of patients thought to have cancer confined to the prostate. This might indicate that cancer cells have already spread but have remained clinically undetected by physicians — or it might suggest a high false positive rate, Dr. Ross notes.
The hope, though, is that the blood test can be used to predict which cancer treatments are effective for individual patients, which have stopped working and what new approaches to try next — without performing biopsies. “This is analogous to using a PSA test to determine whether or not surgery to remove a tumor was successful. In that way, it may eventually be possible to use this new blood test as a signpost to follow cancer cell counts in patients before and after treatment to determine how well they are reacting to it,” says Dr. Ross.